Cells in culture, stained for keratin (red) and DNA (green)

The cell is the structural and functional unit of all living organisms, and are sometimes called the "building blocks of life." Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, (humans have an estimated 100,000 billion or 10¹⁴ cells). The cell theory, first developed in 1839 by Schleiden and Schwann, states that all organisms are composed of one or more cells; all cells come from preexisting cells; all vital functions of an organism occur within cells and that cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells. Cultured MDCK epithelial cells were stained for keratin, desmoplakin, and DNA. The stained cells were visualized by scanning laser confocal microscopy. ... Cultured MDCK epithelial cells were stained for keratin, desmoplakin, and DNA. The stained cells were visualized by scanning laser confocal microscopy. ... Stain has several possible meanings: A stain can be an unwanted localized discoloration, often in fabrics or textiles. ... Microscopic view of stained keratin. ... Jump to: navigation, search Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Jump to: navigation, search Life is a multi-faceted concept. ... Jump to: navigation, search In biology and ecology, an organism (in Greek organon = instrument) is an assembly of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Jump to: navigation, search Binomial name Homo sapiens Linnaeus, 1758 Subspecies Homo sapiens idaltu (extinct) Homo sapiens sapiens For other uses, see Human (disambiguation). ... Multicellular organisms are those organisms containing more than one cell, and having differentiated cells that perform specialized functions. ... Much like the atomic theory forms the foundation of physics, the cell theory is the basis of modern biology. ... Die Entwickelung der Meduse (The Development of the Medusas), in Schleidens Das Meer Matthias Jakob Schleiden (April 5, 1804 - June 23, 1881) was a German botanist and co-founder of the cell theory. ... Jump to: navigation, search Theodor Schwann (December 7, 1810 - January 11, 1882) was a German physiologist, histologist and cytologist. ... Jump to: navigation, search In biology and ecology, an organism (in Greek organon = instrument) is an assembly of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Jump to: navigation, search Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ...

The word cell comes from the Latin cella, a small room. The name was chosen by Robert Hooke when he compared the cork cells he saw to small rooms monks lived in. Jump to: navigation, search A cell is a single unit or compartment, enclosed by a border or wall. ... Jump to: navigation, search Latin is an Indo-European language originally spoken in the region around Rome called Latium. ... Jump to: navigation, search Robert Hooke, FRS (July 18, 1635 - March 3, 1703), one of the greatest experimental scientists of the seventeenth century, played an important role in the scientific revolution. ... Jump to: navigation, search A cork stopper for a wine bottle A Champagne cork Cork material is a subset of generic cork tissue, harvested for commercial use primarily from the Cork Oak tree, Quercus suber, with Portugal producing most cork worldwide. ...

Overview

Properties of cells

Mouse cells grown in a culture dish. These cells grow in large clumps but each individual cell is about 10 micrometres across.

Each cell is at least somewhat self-contained and self-maintaining: it can take in nutrients, convert these nutrients into energy, carry out specialized functions, and reproduce as necessary. Each cell stores its own set of instructions for carrying out each of these activities. Image of cell with size scale from wikibook Cell Biology textbook (licensed under the GFDL): http://wikibooks. ... Image of cell with size scale from wikibook Cell Biology textbook (licensed under the GFDL): http://wikibooks. ... A micrometre (American spelling: micrometer), symbol µm, is an SI unit of length. ...

All cells share several abilities:

• Reproduction by cell division.
• Metabolism, including taking in raw materials, building cell components, creating energy, molecules and releasing by-products. The functioning of a cell depends upon its ability to extract and use chemical energy stored in organic molecules. This energy is derived from metabolic pathways.
• Synthesis of proteins, the functional workhorses of cells, such as enzymes. A typical mammalian cell contains up to 10,000 different proteins.
• Response to external and internal stimuli such as changes in temperature, pH or nutrient levels.
• Traffic of vesicles.

Cell division is the process by which a cell (called the parent cell) divides into two cells (called daughter cells). ... A few of the metabolic pathways in a cell. ... Jump to: navigation, search A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... A by-product is a secondary or incidental product deriving from a manufacturing process or chemical reaction, and is not the primary product or service being produced. ... In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, to achieve in either the formation of a metabolic product to be used or stored by the cell, or the initiation of another metabolic pathway (then called a flux generating step). ... An overview of protein synthesis. ... Jump to: navigation, search A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Jump to: navigation, search Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... Jump to: navigation, search Orders Subclass Multituberculata (extinct) Plagiaulacida Cimolodonta Subclass Palaeoryctoides (extinct) Subclass Triconodonta (extinct) Subclass Placentalia Afrosoricida Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Litopterna (extinct) Macroscelidea Mesonychia (extinct) Notoungulata (extinct) Perissodactyla Pholidota Plesiadapiformes (extinct) Primates Proboscidea... Jump to: navigation, search A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Jump to: navigation, search In biology, signal transduction is any process by which a cell converts one kind of signal or stimulus into another. ... Jump to: navigation, search The title of this article is shown beginning with a capital letter due to technical restrictions. ... The aggregation of things (e. ... Jump to: navigation, search In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...

Types of cells

The cells of eukaryotes and prokaryotes. - This figure illustrates a typical human cell (eukaryote) and a typical bacterium (prokaryote). The drawing on the left highlights the internal structures of eukaryotic cells, including the nucleus (light blue), the nucleolus (intermediate blue), mitochondria (orange), and ribosomes (dark blue). The drawing on the right demonstrates how bacterial DNA is housed in a structure called the nucleoid (very light blue), as well as other structures normally found in a prokaryotic cell, including the cell membrane (black), the cell wall (intermediate blue), the capsule (orange), ribosomes (dark blue), and a flagellum (also black).

One way to classify cells is whether they live alone or in groups. Organisms vary from single cells (called single-celled or unicellular organisms) that function and survive more or less independently, through colonial forms with cells living together, to multicellular forms in which cells are specialized. 220 types of cells and tissues make up the multicellular human body. == Headline texiuvvp;iyppp;iv--24. ... == Headline texiuvvp;iyppp;iv--24. ... Jump to: navigation, search In biology and ecology, an organism (in Greek organon = instrument) is an assembly of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Jump to: navigation, search Binomial name Homo sapiens Linnaeus, 1758 Subspecies Homo sapiens idaltu (extinct) Homo sapiens sapiens For other uses, see Human (disambiguation). ...

Cells can also be classified into two categories based on their internal structure.

• Prokaryotic cells are structurally simple. They are found only in single-celled and colonial organisms. In the three-domain system of scientific classification, prokaryotic cells are placed in the domains Archaea and Eubacteria.

• Eukaryotic cells have organelles with their own membranes. Single-celled eukaryotic organisms such as amoebae and some fungi are very diverse, but many colonial and multicellular forms such as plants, animals, and brown algae also exist.

Jump to: navigation, search Prokaryotes (from Old Greek pro- before + karyon nut, referring to the cell nucleus, + suffix -otos, pl. ... In biology, a colony (from Latin colonia) means several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defences, the ability to attack bigger prey etc. ... The three-domain system is a biological classification introduced by Carl Woese in 1990 that emphasizes his separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria. ... Jump to: navigation, search Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Jump to: navigation, search Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea are a major division of living organisms. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria is also the fictional name of a warring nation under Benzino Napaloni as dictator, in the 1940 film The Great Dictator... Jump to: navigation, search Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (also spelled eucaryote) is an organism with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Jump to: navigation, search Schematic of typical animal cell, showing subcellular components. ... Amoeba is a genus of protozoa that moves by means of temporary projections called pseudopods, and is well-known as a representative unicellular organism. ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... Jump to: navigation, search Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants... Jump to: navigation, search Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Subregnum Bilateria  Acoelomorpha  Orthonectida  Rhombozoa  Myxozoa  Superphylum Deuterostomia     Chordata (vertebrates, etc. ... Orders Dictyotales Desmerestiales Fucales Laminariales (kelps) etc. ...

Subcellular components

Schematic of typical animal cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle,(5) rough endoplasmic reticulum (ER), (6) Golgi apparatus, (7) Cytoskeleton, (8) smooth ER, (9) mitochondria, (10) vacuole, (11) cytoplasm, (12) lysosome, (13) centrioles

Schematic of typical plant cell (see table 2 for a comparison between plant and animal cells)

All cells whether prokaryotic or eukaryotic have a membrane, which envelopes the cell, separates its interior from its environment, controls what moves in and out, and maintains the electric potential of the cell. Inside the membrane, a salty cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditary material of genes and RNA, which contain the information necessary to build various proteins such as enzymes, the cell's primary machinery. There are also other kinds of biomolecules in cells. This article will list these primary components of the cell then briefly describe their function. Image File history File links Diagram of a typical animal cell. ... Image File history File links Diagram of a typical animal cell. ... Jump to: navigation, search Schematic of typical animal cell, showing subcellular components. ... -1... Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Jump to: navigation, search In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Jump to: navigation, search The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ... Jump to: navigation, search In cell biology, the Golgi apparatus, Golgi body, Golgi complex, or dictyosome is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ... The cytoskeleton is a cellular scaffolding or skeleton contained, as all other organelles, within the cytoplasm. ... Jump to: navigation, search Mitochondria are visible as thread-like structures in the light microscope. ... Jump to: navigation, search Vacuoles are large membrane-bound compartments within some eukaryotic cells where they serve a variety of different functions: capturing food materials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to the cell, maintaining fluid balance (called turgor) within the cell, exporting... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... Jump to: navigation, search Lysosomes contain digestive enzymes (acid hydrolases) to digest macromolecules. ... Jump to: navigation, search The centriole is the smallest part of a cell. ... Download high resolution version (1024x815, 364 KB) <image=plantwithvisablecell> File links The following pages link to this file: Cell (biology) Plant cell ... Download high resolution version (1024x815, 364 KB) <image=plantwithvisablecell> File links The following pages link to this file: Cell (biology) Plant cell ... Jump to: navigation, search Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... In biological cells that are electrically at rest, the cytosol possesses a uniform electric potential or voltage compared to the extracellular solution. ... Jump to: navigation, search In chemistry, salt is a term used for ionic compounds composed of positively charged cations and negatively charged anions, so that the product is neutral and without a net charge. ... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... Jump to: navigation, search Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Jump to: navigation, search This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... Jump to: navigation, search Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... Jump to: navigation, search Gene expression (also protein expression or often simply expression) is the process by which a genes information is converted into the structures and functions of a cell. ... Jump to: navigation, search A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Jump to: navigation, search Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

Cell membrane - a cell's protective coat

Main article: Cell membrane Jump to: navigation, search Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ...

The cytoplasm of a eukaryotic cell is surrounded by a plasma membrane. A form of plasma membrane is also found in prokaryotes, but is usually referred to as the cell membrane. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of lipids (fat-like molecules) and proteins. Embedded within this membrane are a variety of other molecules that act as channels and pumps, moving different molecules into and out of the cell. A DPPC bilayer simulation Color scheme: PO4 = green, N(CH3)3 = violet, water = blue, terminal CH3 = yellow, O = red, glycol C = brown, chain C = grey In biology and chemistry, a lipid bilayer is a membrane or zone of a membrane composed of lipid molecules (usually phospholipids). ... Jump to: navigation, search A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

Cytoskeleton - a cell's scaffold

Main article: Cytoskeleton The cytoskeleton is a cellular scaffolding or skeleton contained, as all other organelles, within the cytoplasm. ...

The cytoskeleton is an important, complex, and dynamic cell component. It acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell; and moves parts of the cell in processes of growth and motility. There are a great number of proteins associated with the cytoskeleton, each controlling a cell's structure by directing, bundling, and aligning filaments. Jump to: navigation, search sperm is a process whereby cells absorb material (molecules or other cells) from outside by engulfing it with their cell membranes. ...

Genetic material

Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long term information storage, but some viruses (retroviruses) have RNA as their genetic material. The biological information contained in an organism is encoded in its DNA or RNA sequence. RNA is also used for information transport (e.g. mRNA) and enzymatic functions (e.g. ribosomal RNA) in organisms that use RNA for the genetic code itself. Jump to: navigation, search Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Jump to: navigation, search Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... Jump to: navigation, search Genera Alpharetrovirus Betaretrovirus Gammaretrovirus Deltaretrovirus Epsilonretrovirus Lentivirus Spumavirus A Retrovirus is a virus which has a genome consisting of two plus sense RNA molecules, which may or may not be identical. ... Jump to: navigation, search RNA codons. ... The interaction of mRNA in a eukaryote cell. ... Jump to: navigation, search Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ...

Prokaryotic genetic material is organized in a simple circular DNA molecule (the bacterial chromosome) in the nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like mitochondria and chloroplasts (see endosymbiotic theory). Jump to: navigation, search Figure 1: Chromosome. ... In prokaryotic lifeforms, the nucleoid region is the part of the cell that contains the DNA molecule. ... Jump to: navigation, search Figure 1: Chromosome. ... Jump to: navigation, search The endosymbiotic theory concerns the origins of mitochondria and chloroplasts, which are organelles of eukaryotic cells. ...

A human cell, e.g. has genetic material in the nucleus (the nuclear genome) and in the mitochondria (the mitochondrial genome). The nuclear genome is divided into 46 linear DNA molecules called chromosomes. The mitochondrial genome is a circular DNA molecule separate from the nuclear DNA. Although the mitochondrial genome is very small, it codes for some important proteins. In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... The mitochondrial genome is the genetic material of the mitochondria. ...

Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called transfection. This can be transient, if the DNA is not inserted into the cell's genome, or stable, if it is. Introducing DNA into eukaryotic cells, such as animal cells, is called transfection. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...

Organelles

Main article: Organelle Jump to: navigation, search Schematic of typical animal cell, showing subcellular components. ...

The human body contains many different organs, such as the heart, lung, and kidney, with each organ performing a different function. Cells also have a set of "little organs", called organelles, that are adapted and/or specialized for carrying out one or more vital functions. Membrane-bound organelles are only found in eukaryotes. In biology, an organ (Latin: organum, instrument, tool) is a group of tissues, which perform a specific function or group of functions. ... Jump to: navigation, search Schematic of typical animal cell, showing subcellular components. ...

• Cell nucleus - a cell's information center: The cell nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes and is the place where almost all DNA replication and RNA synthesis occur. The nucleus is spheroid in shape and separated from the cytoplasm by a double membrane called the nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or copied into a special RNA, called mRNA. This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. In prokaryotes, DNA processing takes place in the cytoplasm.

• Ribosomes - the protein production machine: Ribosomes are found in both prokaryotes and eukaryotes. The ribosome is a large complex composed of many molecules, including RNAs and proteins, and is responsible for processing the genetic instructions carried by an mRNA. The process of converting an mRNA's genetic code into the exact sequence of amino acids that make up a protein is called translation. Protein synthesis is extremely important to all cells, and therefore a large number of ribosomes—sometimes hundreds or even thousands—can be found throughout a cell.

• Mitochondria and chloroplasts - the power generators: Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. As mentioned earlier, mitochondria contain their own genome that is separate and distinct from the nuclear genome of a cell. Mitochondria play a critical role in generating energy in the eukaryotic cell, and this process involves a number of complex metabolic pathways. Chloroplasts are larger than mitochondria, and convert solar energy into a chemical energy ("food") via photosynthesis. Like mitochondria, chloroplasts have their own genome. Chloroplasts are found only in photosynthetic eukaryotes like plants and algae. There are a number of plant organelles that are modified chloroplasts; they are broadly called plastids and are often involved in storage.

• Endoplasmic reticulum and Golgi apparatus - macromolecule managers:: The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that will float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface, and the smooth ER, which lacks them. Translation of the mRNA for those proteins that will either stay in the ER or be exported from the cell occurs at the ribosomes attached to the rough ER. The smooth ER is important in lipid synthesis, detoxification and as a calcium reservoir. The Golgi apparatus, sometimes called a Golgi body or Golgi complex is the central delivery system for the cell and is a site for protein processing, packaging, and transport. Both organelles consist largely of heavily folded membranes.

• Lysosomes and peroxisomes - the cellular digestive system: Lysosomes and peroxisomes are often referred to as the garbage disposal system of a cell. Both organelles are somewhat spherical, bound by a single membrane, and rich in digestive enzymes, naturally occurring proteins that speed up biochemical processes. For example, lysosomes can contain more than three dozen enzymes for degrading proteins, nucleic acids, and certain sugars called polysaccharides. Here we can see the importance behind compartmentalization of the eukaryotic cell. The cell could not house such destructive enzymes if they were not contained in a membrane-bound system.

• Centrioles - They help in the formation of mitotic appratus. Two centrioles are present in the animal cells. They are also found in some fungi and algae cells.

Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... HELLO INDIA Synonyms: karyotheca, nuclear membrane, nucleolemma, perinuclear envelope Categories: Cell biology stubs ... Transcription may be one of the following: In linguistics, transcription is the conversion of spoken words into written language. ... Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ... Jump to: navigation, search Mitochondria are visible as thread-like structures in the light microscope. ... In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, to achieve in either the formation of a metabolic product to be used or stored by the cell, or the initiation of another metabolic pathway (then called a flux generating step). ... Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... In chemistry, a chemical bond is the force which holds together atoms in molecules or crystals. ... Jump to: navigation, search Leaf. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Jump to: navigation, search Plastids are major organelles found only in plants and algae. ... Jump to: navigation, search The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ... Jump to: navigation, search Figure 1: Structure of a Lipid. ... Detox, short for detoxification, in general is the removal of toxic substances. ... Jump to: navigation, search General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... Jump to: navigation, search In cell biology, the Golgi apparatus, Golgi body, Golgi complex, or dictyosome is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ... Jump to: navigation, search Lysosomes contain digestive enzymes (acid hydrolases) to digest macromolecules. ... Peroxisomes are ubiquitous organelles in eukaryotes. ... Jump to: navigation, search Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ...

Anatomy of cells

Prokaryotic cells

Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack most of the intracellular organelles and structures that are characteristic of eukaryotic cells (an important exception is the ribosomes, which are present in both prokaryotic and eukaryotic cells). Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili—proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. Other differences include: Jump to: navigation, search Prokaryotes (from Old Greek pro- before + karyon nut, referring to the cell nucleus, + suffix -otos, pl. ... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Image of bacteriological pili or fimbriae A pilus (Latin; plural : pili) is a hairlike structure on the surface of a cell, especially Gram-negative bacteria, a protein appendage required for bacterial conjugation. ... The cell envelope is the cell membrane and cell wall plus an outer membrane, if one is present. ... Jump to: navigation, search A cell wall is a more or less solid layer surrounding a cell. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...

• The plasma membrane (a phospholipid bilayer) separates the interior of the cell from its environment and serves as a filter and communications beacon.
• Most prokaryotes have a cell wall (some exceptions are Mycoplasma (a bacterium) and Thermoplasma (an archaeon)). It consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from "exploding" from osmotic pressure against a hypotonic environment. A cell wall is also present in some eukaryotes like fungi, but has a different chemical composition
• A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease). Even without a real nucleus, the DNA is condensed in a nucleoid. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Plasmids can carry additional functions, such as antibiotic resistance.

Jump to: navigation, search A cell wall is a more or less solid layer surrounding a cell. ... Species M. genitalium M. hominis M. pneumoniae etc. ... Jump to: navigation, search Species Darland , 1970 Sergerer , 1988 Thermoplasma is a genus of archaea. ... Peptidoglycan, also known as murein, is a substance that forms a homogeneous layer lying outside the plasma membrane in prokaryotes. ... Turgor (also called turgor pressure or osmotic pressure) is the pressure produced in a space that is enclosed by a semipermeable membrane. ... In biology, a hypotonic cell environment is one with a lower concentration of solutes than the cytoplasm. ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... Jump to: navigation, search Adult deer ticks can be carriers of Lyme disease. ... Jump to: navigation, search Figure 1 : Schematic drawing of a bacterium with plasmids enclosed. ...

Eukaryotic cells

There are two types of cells, eukaryotic and prokaryotic. Eukaryotic cells are usally found in multi-cellular organisms, while prokaryotic cells are usually on their own. Eukaryotic cells are about 10 times the size of a typical prokaryote and can be as much as 1000 times greater in volume. The major difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Most important among these is the presence of a nucleus, a membrane-delineated compartment that houses the eukaryotic cell's DNA. It is this nucleus that gives the eukaryote its name, which means "true nucleus." Other differences include: Jump to: navigation, search Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (also spelled eucaryote) is an organism with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Jump to: navigation, search Nucleus can mean: The Nuclear Envelope The nucleus is enveloped by a pair of membranes enclosing a lumen that is continuous with that of the endoplasmic reticulum. ...

• The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may or may not be present.
• The eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are highly condensed (i.e. folded around histones). All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles can contain some DNA.
• Eukaryotes can move using cilia or flagella. The flagella are more complex than those of prokaryotes.

Jump to: navigation, search Figure 1: Chromosome. ... Jump to: navigation, search In biology, histones are the chief proteins of chromatin. ... Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... Jump to: navigation, search Schematic of typical animal cell, showing subcellular components. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Jump to: navigation, search Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea are a major division of living organisms. ... Jump to: navigation, search Typical phyla Rhodophyta (red algae) Chromista Heterokontophyta (heterokonts) Haptophyta Cryptophyta (cryptomonads) Alveolates Dinoflagellata Apicomplexa Ciliophora (ciliates) Excavates Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Amoebozoa Choanozoa Many others; classification varies Protists are a heterogeneous group of living things, comprising those eukaryotes that are neither animals, plants... Jump to: navigation, search Divisions Chytridiomycota Zygomycota Glomeromycota Ascomycota Basidiomycota Yellow fungus Fungus growing on a tree in Borneo For the fictional character, see Fungus the Bogeyman. ... Jump to: navigation, search Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants... Jump to: navigation, search Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Subregnum Bilateria  Acoelomorpha  Orthonectida  Rhombozoa  Myxozoa  Superphylum Deuterostomia     Chordata (vertebrates, etc. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length. ... Jump to: navigation, search A sperm cell, spermatozoon ( spermatozoa) (in Greek: sperma = semen and zoon = alive), or spermatozoan, is the haploid cell that is the male gamete. ... Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... In prokaryotic lifeforms, the nucleoid region is the part of the cell that contains the DNA molecule. ... Jump to: navigation, search Figure 1: Chromosome. ... Jump to: navigation, search In biology, histones are the chief proteins of chromatin. ... Jump to: navigation, search A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... The cytoskeleton is a cellular scaffolding or skeleton contained, as all other organelles, within the cytoplasm. ... Jump to: navigation, search Chemotaxis is the phenomenon in which bodily cells, bacteria, and other single-celled or multicellular organisms direct their movements according to certain chemicals in their environment. ... Jump to: navigation, search A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Flagellin is a protein that arranges itself in a hollow cylinder to form the filament in bacterial flagellum. ... Jump to: navigation, search cross-section of two motile cilia, showing the 9+2 structure A cilium (plural cilia) is an organelle projecting from a eukaryotic cell. ... Tubulin is the protein which makes up microtubules. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Jump to: navigation, search The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Jump to: navigation, search Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants... Cell division is the process by which a cell (called the parent cell) divides into two cells (called daughter cells). ... Binary fission Binary fission is the asexual reproductive process used by most prokaryotes, which results in the reproduction of a living cell by division into two equal, or near equal, parts. ... Jump to: navigation, search Light micrograph of a newt lung cell in early anaphase of mitosis. ... -1... Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... -1... Jump to: navigation, search The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ... Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... The cytoskeleton is a cellular scaffolding or skeleton contained, as all other organelles, within the cytoplasm. ... Jump to: navigation, search In cell biology, the Golgi apparatus, Golgi body, Golgi complex, or dictyosome is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... Jump to: navigation, search Mitochondria are visible as thread-like structures in the light microscope. ... Jump to: navigation, search In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Jump to: navigation, search Vacuoles are large membrane-bound compartments within some eukaryotic cells where they serve a variety of different functions: capturing food materials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to the cell, maintaining fluid balance (called turgor) within the cell, exporting... Jump to: navigation, search Lysosomes contain digestive enzymes (acid hydrolases) to digest macromolecules. ... Jump to: navigation, search The centriole is the smallest part of a cell. ... Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... -1... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... The cytoskeleton is a cellular scaffolding or skeleton contained, as all other organelles, within the cytoplasm. ... Jump to: navigation, search In cell biology, the Golgi apparatus, Golgi body, Golgi complex, or dictyosome is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ... In cell biology, the Golgi apparatus, Golgi body, Golgi complex, or dictyosome is an organelle found in most eukaryotic cells, including those of plants and animals (but not most fungi). ... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... Jump to: navigation, search Mitochondria are visible as thread-like structures in the light microscope. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Jump to: navigation, search The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... Jump to: navigation, search Plastids are major organelles found only in plants and algae. ... Vacuoles are large membrane-bound compartments within some eukaryotic cells where they serve a variety of different functions: capturing food materials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to the cell, maintaining fluid balance (called turgor) within the cell, exporting unwanted substances from the... Vacuoles are large membrane-bound compartments within some eukaryotic cells where they serve a variety of different functions: capturing food materials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to the cell, maintaining fluid balance (called turgor) within the cell, exporting unwanted substances from the... Peroxisomes are ubiquitous organelles in eukaryotes. ... A membrane-surrounded plant cell organelle, especially found in germinating seeds, and involved in the breakdown and conversion of fatty acids to acetyl-CoA for the glyoxylate bypass. ... Jump to: navigation, search cross-section of two motile cilia, showing the 9+2 structure A cilium (plural cilia) is an organelle projecting from a eukaryotic cell. ... Jump to: navigation, search A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Jump to: navigation, search A cell wall is a more or less solid layer surrounding a cell. ... Jump to: navigation, search Plasmodesmata (Singular, plasmodesma) are small cell junctions in a plant cell which connect the cytoplasm of adjacent plant cells, forming a circulatory and communication system connecting the cells in plant tissue. ... Jump to: navigation, search A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ...

Cell functions

Cell growth and metabolism

Main articles: Cell growth, Cell metabolism The term cell growth is used in two different ways in biology. ... A few of the metabolic pathways in a cell. ...

Between successive cell divisions cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions; catabolism, in which the cell breaks down complex molecules to produce energy and reducing power, and anabolism, where the cell uses energy and reducing power to construct complex molecules and perform other biological functions. Complex sugars consumed by the organism can be broken down into a less chemically complex sugar molecule called glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, via two different pathways. Anabolism is the aspect of metabolism that contributes to growth. ... Anabolism is the aspect of metabolism that is characterized by growth. ... Jump to: navigation, search Glucose (Glc), a simple monosaccharide sugar, is one of the most important carbohydrates and is used as a source of energy in animals and plants. ... Jump to: navigation, search Adenosine 5-triphosphate (ATP) is the nucleotide known in biochemistry as the molecular currency of intracellular energy transfer; that is, ATP is able to store and transport chemical energy within cells. ...

The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. Each reaction is designed to produce some hydrogen ions that can then be used to make energy packets (ATP). In prokaryotes, glycolysis is the only method used for converting energy. The second pathway, called the Krebs cycle, or citric acid cycle, occurs inside the mitochondria and is capable of generating enough ATP to run all the cell functions. Glycolysis is a term referring to a series of biochemical reactions by which a molecule of glucose is oxidized to two molecules of pyruvic acid. ... Glycolysis is the initial metabolic pathway of carbohydrate catabolism. ... Jump to: navigation, search The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle) is a series of chemical reactions of central importance in all living cells that utilize oxygen as part of cellular respiration. ...

Making new cells

Main article: Cell division Cell division is the process by which a cell (called the parent cell) divides into two cells (called daughter cells). ...

An overview of protein synthesis.
Within the nucleus of the cell (light blue), genes (DNA, dark blue) are transcribed into RNA. This RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA (red) that is then transported out of the nucleus and into the cytoplasm (peach), where it undergoes translation into a protein. mRNA is translated by ribosomes (purple) that match the three-base codons of the mRNA to the three-base anti-codons of the appropriate tRNA. Newly synthesized proteins (black) are often further modified, such as by binding to an effector molecule (orange), to become fully active.

Cell division involves a single cell (called a mother cell) dividing into two daughter cells. This leads to growth in multicellular organisms (the growth of tissue) and to procreation (vegetative reproduction) in unicellular organisms. Prokaryotic cells divide by binary fission. Eukaryotic cells usually undergo a process of nuclear division, called mitosis, followed by division of the cell, called cytokinesis. A diploid cell may also undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular organisms, fusing to form new diploid cells. DNA replication, or the process of duplicating a cell's genome, is required every time a cell divides. Replication, like all cellular activities, requires specialized proteins for carrying out the job. File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... Jump to: navigation, search This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... Jump to: navigation, search Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately leads to the translation of the genetic code (via... Jump to: navigation, search Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... The interaction of mRNA in a eukaryote cell. ... Jump to: navigation, search Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ... Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... RNA codons. ... Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... Multicellular organisms are those organisms containing more than one cell, and having differentiated cells that perform specialized functions. ... Biological tissue is a substance made up of cells that perform a similar function. ... Production of new individuals along a leaf margin of the air plant, Kalanchoë pinnata. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... Jump to: navigation, search Prokaryotes (from Old Greek pro- before + karyon nut, referring to the cell nucleus, + suffix -otos, pl. ... Binary fission Binary fission is the asexual reproductive process used by most prokaryotes, which results in the reproduction of a living cell by division into two equal, or near equal, parts. ... Jump to: navigation, search Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (also spelled eucaryote) is an organism with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Jump to: navigation, search Light micrograph of a newt lung cell in early anaphase of mitosis. ... A cell that has almost completed cytokinesis. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... -1... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Gametes (in Greek: γαμέτες) —also known as sex cells, or spores—are the specialized germ cells that come together during fertilization (conception) in organisms that reproduce sexually. ... Jump to: navigation, search DNA replication. ...

Protein synthesis

Main article: Protein biosynthesis An overview of protein synthesis. ...

Protein synthesis is the process in which the cell builds proteins. DNA transcription refers to the synthesis of a messenger RNA (mRNA) molecule from a DNA template. This process is very similar to DNA replication. Once the mRNA has been generated, a new protein molecule is synthesized via the process of translation. Jump to: navigation, search A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Jump to: navigation, search Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately leads to the translation of the genetic code (via... Jump to: navigation, search The life cycle of an mRNA in a eukaryotic cell. ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ...

The cellular machinery responsible for synthesizing proteins is the ribosome. The ribosome consists of structural RNA and about 80 different proteins. When the ribosome encounters an mRNA, the process of translating an mRNA to a protein begins. The ribosome accepts a new transfer RNA, or tRNA—the adaptor molecule that acts as a translator between mRNA and protein—bearing an amino acid, the building block of the protein. Another site binds the tRNA that becomes attached to the growing chain of amino acids, forming the a polypeptide chain that will eventually be processed to become a protein. Jump to: navigation, search Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ... Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... Jump to: navigation, search In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ...

Origins of cells

Main article: Origin of life Jump to: navigation, search Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. ...

The origin of cells has to do with the origin of life, and was one of the most important steps in evolution of life as we know it. The birth of the cell marked the passage from prebiotic chemistry to biological life.

Origin of first cell

If life is viewed from the point of view of replicators, that is DNA molecules in the organism, cells satisfy two fundamental conditions: protection from the outside environment and confinement of biochemical activity. The former condition is needed to maintain the fragile DNA chains stable in a varying and sometimes aggressive environment, and may have been the main reason for which cells evolved. The latter is fundamental for the evolution of biological complexity. If freely-floating DNA molecules that code for enzymes that are not enclosed into cells, the enzymes that advantage a given DNA molecule (for example, by producing nucleotides) will automatically advantage the neighbouring DNA molecules. This might be viewed as "parasitism by default". Therefore the selection pressure on DNA molecules will be much lower, since there is not a definitive advantage for the "lucky" DNA molecule that produces the better enzyme over the others: all molecules in a given neighbourhood are almost equally advantaged. In a generic sense, a replicator can be anything capable of self-replication. ... Jump to: navigation, search Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Jump to: navigation, search Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Jump to: navigation, search Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... Parasitism (in Greek: παρασσυτισμός) is an interaction between two organisms, in which one organism (the parasite) benefits and the other (the host) is harmed. ... Jump to: navigation, search Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. ...

If all the DNA molecule is enclosed in a cell, then the enzymes coded from the molecule will be kept close to the DNA molecule itself. The DNA molecule will directly enjoy the benefits of the enzymes it codes, and not of others. This means other DNA molecules won't benefit from a positive mutation in a neighbouring molecule: this in turn means that positive mutations give immediate and selective advantage to the replicator bearing it, and not on others. This is thought to have been the one of the main driving force of evolution of life as we know it. (Note. This is more a metaphor given for simplicity than complete accuracy, since the earliest molecules of life, probably up to the stage of cellular life, were most likely RNA molecules, acting both as replicators and enzymes: see RNA world hypothesis . But the core of the reasoning is the same.) Jump to: navigation, search Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... The RNA world hypothesis proposes that RNA was actually the first life-form on earth, later developing a cell membrane around it and becoming the first prokaryotic cell. ...

Biochemically, cell-like spheroids formed by proteinoids are observed by heating amino acids with phosphoric acid as a catalyst. They bear much of the basic features provided by cell membranes. Proteinoid-based protocells enclosing RNA molecules could (but not necessarily should) have been the first cellular life forms on Earth. Proteinoids are protein-like molecules formed inorganically from amino acids. ... Jump to: navigation, search In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... Jump to: navigation, search R-phrases S-phrases , , Supplementary data page Structure and properties n, εr, etc. ... Jump to: navigation, search Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ...

Another theory holds that the turbulent shores of the ancient coastal waters may have served as a mammoth laboratory, aiding in the countless experiments necessary to bring about the first cell. Waves breaking on the shore create a delicate foam composed of bubbles. Winds sweeping across the ocean have a tendancy to drive things to shore, much like driftwood collecting on the beach. It is possible that organic molecules were concentrated on the shorelines in much the same way. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles comprised of mostly water tend to burst quickly, oily bubbles happen to be much more stable, lending more time to the particular bubble to perform these crucial experiments. The Phospholipid is a good example of a common oily compound prevalent in the prebiotic seas. Phospholipids can be constructed in ones mind as a hydrophilic head on one end, and a hydrophobic tail on the other. Phospholipids also possess an important characteristic, that is being able to link together to form a bilayer membrane. A lipid monolayer bubble can only contain oil, and is therefore not conducive to harbouring water-soluble organic molecules. On the other hand, a lipid bilayer bubble [1] can contain water, and was a likely precursor to the modern cell membrane. If a protein came along that increased the integrity of its parent bubble, then that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the experiment into the surrounding medium. Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multi-celluar organisms could be acheived. This theory is expanded upon in the book, "The Cell: Evolution of the First Organism" by Joseph Panno Ph.D. Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... Two schematic representations of a phospholipid. ... The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... A DPPC bilayer simulation Color scheme: PO4 = green, N(CH3)3 = violet, water = blue, terminal CH3 = yellow, O = red, glycol C = brown, chain C = grey In biology and chemistry, a lipid bilayer is a membrane or zone of a membrane composed of lipid molecules (usually phospholipids). ... Jump to: navigation, search Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. ... Prokaryotes are unicellular (in rare cases, multicellular) organisms without a nucleus. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ...

Origin of eukaryotic cells

The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. It is almost certain that DNA-bearing organelles like the mitochondria and the chloroplasts are what remains of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, where the rest of the cell seems to be derived from an ancestral archaean prokaryote cell – a theory termed the endosymbiotic theory. Common Clownfish (Amphiprion ocellaris) in their magnificent sea anemone (Heteractis magnifica) home. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... Jump to: navigation, search Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea are a major division of living organisms. ... Jump to: navigation, search The endosymbiotic theory concerns the origins of mitochondria and chloroplasts, which are organelles of eukaryotic cells. ...

There is still considerable debate on if organelles like the hydrogenosome predated the origin of mitochondria, or viceversa : see the hydrogen hypothesis for the origin of eukaryotic cells. A hydrogenosome is an organelle of ciliates, trichomonads and fungi. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... The Hydrogen hypothesis is a model that describes how the first eukaryotic cell may have developed. ...

History

• 1632-1723: Antony van Leeuwenhoek teaches himself to grind lenses, builds a microscope and draws protozoa, such as Vorticella from rain water, and bacteria from his own mouth.
• 1665 : Robert Hooke discovers cells in cork, then in living plant tissue using an early microscope.

...I could exceedingly plainly perceive it to be all perforated and porous, much like honeycomb...these pores or cells, were not very deep, but consisted of a great many little boxes... – Hooke describing his observations on a thin slice of cork.

• 1839 : Theodor Schwann and Matthias Jakob Schleiden elucidate the principal that plants and animals are made of cells, concluding that cells are a common unit of structure and development, thus founding the Cell Theory.
• The belief that life forms are able to occur spontaneously (generatio spontanea) is contradicted by Louis Pasteur (1822-1895).
• Rudolph Virchow states that cells always emerge from cell divisions (omnis cellula ex cellula).
• 1931: Ernst Ruska builds first transmission electron microscope (TEM) at the University of Berlin. By 1935 he has built an EM with twice the resolution of a light microscope, revealing previously unresolvable organelles.
• 1953: Watson and Crick made their first announcement on the double-helix structure for DNA on February 28.
• 1981: Lynn Margulis published Symbiosis in Cell Evolution detailing the endosymbiotic theory.

Anton von Leeuwenhoek Anton van Leeuwenhoek (October 24, 1632 _ August 26, 1723) was a tradesman and scientist from Delft, in the Netherlands. ... Jump to: navigation, search A lens. ... Jump to: navigation, search 1852 microscope Compound microscope made by John Cuff in 1750 A microscope (Greek: micron = small and scopos = aim) is an instrument for viewing objects that are too big to be seen by the naked or unaided eye. ... Protozoa (in Greek protos = first and zoon = animal) are single-celled eukaryotes (organisms with nuclei) that show some characteristics usually associated with animals, most notably mobility and heterotrophy. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Jump to: navigation, search Robert Hooke, FRS (July 18, 1635 - March 3, 1703), one of the greatest experimental scientists of the seventeenth century, played an important role in the scientific revolution. ... A pore, in general, is some form of opening, usually very small. ... Jump to: navigation, search Theodor Schwann (December 7, 1810 - January 11, 1882) was a German physiologist, histologist and cytologist. ... Die Entwickelung der Meduse (The Development of the Medusas), in Schleidens Das Meer Matthias Jakob Schleiden (April 5, 1804 - June 23, 1881) was a German botanist and co-founder of the cell theory. ... Jump to: navigation, search Abiogenesis (Greek a-bio-genesis, non biological origins) is, in its most general sense, the hypothetical generation of life from non-living matter. ... Jump to: navigation, search Louis Pasteur (December 27, 1822 – September 28, 1895) was a French microbiologist and chemist. ... Dr. R.L.K. Virchow Rudolf Ludwig Karl Virchow (October 13, 1821, in Schivelbein, Pomerania - September 5, 1902, in Berlin) was a German doctor, pathologist, prehistorian, biologist, and politician. ... Cell division is the process by which a cell (called the parent cell) divides into two cells (called daughter cells). ... Ernst August Friedrich Ruska (December 25, 1906–May 25, 1988) was a German physicist. ... Transmission electron microscopy (TEM) is an imaging technique whereby a beam of electrons is focused onto a specimen causing an enlarged version to appear on a fluorescent screen or layer of photographic film (see electron microscope), or can be detected by a CCD camera. ... There is no institution called the University of Berlin, but there are four universities in Berlin, Germany: Humboldt University of Berlin (Humboldt-Universität zu Berlin) Technical University of Berlin (Technische Universität Berlin) Free University of Berlin (Freie Universität Berlin) Berlin University of the Arts (Universität der Künste Berlin) This is... James Dewey Watson (born April 6, 1928) is one of the discoverers of the structure of the DNA molecule. ... Professor Francis Harry Compton Crick, OM FRS (8 June 1916 – 28 July 2004) was a British physicist, molecular biologist and neuroscientist, most noted for being one of the co- discoverers of the structure of the DNA molecule in 1953, for which he, James Watson and Maurice Wilkins were jointly awarded... A helix (pl: helices), from the Greek word έλικας/έλιξ, is a twisted shape like a spring, screw or a spiral staircase. ... Lynn Margulis (born 1938) is a biologist and a professor at the University of Massachusetts Amherst. ... Jump to: navigation, search The endosymbiotic theory concerns the origins of mitochondria and chloroplasts, which are organelles of eukaryotic cells. ...

See also

• Cariology is the study of the cell nucleus.
• Cytotoxicity
• Plant cell
• How to prepare an onion cell slide
• Cell types
• Syncytium
• Cell culture
• Stem cell
• Plasmolysis
• Cytorrhysis

A cell is a single unit or compartment, enclosed by a border or wall. ... Jump to: navigation, search In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ... Cytotoxicity is the quality of being poisonous to cells. ... Jump to: navigation, search Plant cell structure // Overview The cells of plants are quite different from the cells of the other eukaryotic kingdoms organisms. ... forceps, dye, pin, onion membrane, slide Microscope This activity is one of the first uses of an optical microscope that most students encounter in a biology lab. ... Jump to: navigation, search A cell type is a distinct morphological or functional form of cell. ... In biology, a syncytium is a large region of cytoplasm that contains many nuclei. ... Cells in culture, stained for keratin (red) and DNA (green) Cell culture is the term applied when growing cells in a synthetic environment. ... Jump to: navigation, search Mouse embryonic stem cells. ... Jump to: navigation, search Before Plasmolysis. ... Cytorrhysis is the complete collapse of a plant cells cell wall within plants due to the loss of water through osmosis. ...

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References

• This article contains material from the Science Primer published by the NCBI, which, as a US government publication, is in the public domain [2].

The National Center for Biotechnology Information (NCBI) is part of the US National Library of Medicine (NLM), which is a branch of the US National Institutes of Health. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ...