Protein biosynthesis (synthesis) is the process in which cells build proteins. The term is sometimes used to refer only to protein translation but more often it refers to a multi-step process, beginning with amino acid synthesis and transcription which are then used for translation. Protein biosynthesis, although very similar, differs between prokaryotes and eukaryotes. Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... For the non-biological synthesis of amino acids see: Strecker amino acid synthesis Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the various amino acids are produced from other compounds. ... A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... Prokaryotic bacteria cell structure Prokaryotes (IPA: //) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ...

Amino acid synthesis

Main article: Amino acid synthesis

Amino acids are the monomers which are polymerized to produce proteins. Amino acid synthesis is the set of biochemical processes (metabolic pathways) which build the amino acids from carbon sources like glucose. Not all amino acids may be synthesised by every organism, for example adult humans have to obtain 9 of the 20 amino acids from their diet. For the non-biological synthesis of amino acids see: Strecker amino acid synthesis Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the various amino acids are produced from other compounds. ... A polymer is a long, repeating chain of atoms, formed through the linkage of many molecules called monomers. ... Biochemistry is the chemistry of life. ... In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, and resulting in either the formation of a metabolic product to be used or stored by the cell (metabolic sink), or the initiation of another metabolic pathway (then called a flux generating... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ...

The amino acids are then loaded onto tRNA molecules for use in the process of translation. 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. ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ...

Transcription

Main article: Transcription (genetics)

Transcription is the process by which an mRNA template, encoding the sequence of the protein in the form of a trinucleotide code, is transcribed from the genome to provide a template for translation. Transcription copies the template from one strand of the DNA double helix, called the template strand. A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... The interaction of mRNA in a eukaryote cell. ... For a non-technical introduction to the topic, see Introduction to Genetics. ... 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 structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Template strand is the strand of DNA that the RNA polymerase uses as a guide to build complementry mRNA. This is the complement of the Coding strand. ...

Transcription can be divided into 3 stages: Initiation, Elongation and Termination, each regulated by a large number of proteins such as transcription factors and coactivators that ensure the correct gene is transcribed in response to appropriate signals. In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... A coactivator is a protein that increases gene expression by binding to an activator (or transcription factor) which contains a DNA binding domain. ...

The DNA strand is read in the 3' to 5' direction and the mRNA is transcribed in the 5' to 3' direction by the RNA polymerase. This article does not cite any references or sources. ...

Translation

Main article: Translation (biology)

Protein translation involves the transfer of information from the mRNA into a peptide, composed of amino acids. This process is mediated by the ribosome, with the adaptation of the RNA sequence into amino acids mediated by transfer RNA. Numerous initation and elongation factors also play a role. Translation is the second stage of protein biosynthesis (part of the overall process of gene expression). ... Peptides (from the Greek πεπτος, digestible), are the family of short molecules formed from the linking, in a defined order, of various α-amino acids. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Transfer RNA Transfer RNA (abbreviated tRNA), first hypothesized by Francis Crick, is a small RNA chain (73-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ...

Translation requires a lot of energy, with the hydrolysis of approximately 4 NTP → NDP per amino acid added. (This includes the aminoacylation of the tRNA. Thus, gene expression is highly regulated to ensure that only proteins that are required are translated. Aminoacylation is the process of adding an aminoacyl group to a compound. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the...

Translation involves 3 processes: initiation, elongation, and termination.

Initiation in prokaryotes

The initiation of protein translation involves the assembly of the ribosome and addition of the first amino acid, methionine.

1. The 30S ribosomal subunit attaches to the mRNA, mediated by IF-1 and IF-3 (initiation factors). The 30S ribosome brings with it the P and A site, but the A site is blocked by IF-1 to prevent binding of tRNA. It aligns to the Shine-Dalgarno sequence, which positions the first codon (AUG) in the P site.
2. Next, the specific aminoacyl-tRNA for N-formylmethionine (F-Met) is brought into the P site by IF-2. The anticodon of this tRNA will bind to the AUG codon on the mRNA. Note: this is the only tRNA brought into the P site; all successive aminoacyl-tRNAs will be brought to the A site for peptide elongation.
3. The 50S ribosomal subunit is then brought in to complete the ribosome, and with it, IF-1, IF-2, and IF-3 come off the complex. The A and P site are completed, and the 50S subunit also brings the E (exit) site.

Initiation factors are proteins that bind to the small subunit of the ribosome during the initiation of protein synthesis. ... The Shine-Dalgarno Sequence (AGGAGGU) is the signal for initiation of protein biosynthesis in bacterial mRNA. It is located 5 of the first coding AUG, and consists primarily, but not exclusively, of purines. ... RNA codons. ... Aminoacyl-tRNA is tRNA (also known as transfer ribonucleic acid) to which its cognated amino acid is adhered. ... N-Formylmethionine is an amino acid found in all living cells. ...

Initiation in eukaryotes

The initiation of protein translation in eukaryotes is similar to that of prokaryotes with some modifications.

1. A complex of proteins will connect the 5'cap and 3'PolyA tail, and this complex will recruit the ribosome subunits.
2. There is no Shine-Dalgarno sequence in eukaryotes. Instead, the ribosome scans along the mRNA for the first methionine codon. Similarly, there is no N-formylmethionine in eukaryotic cells.

Elongation

Elongation of protein biosynthesis is fairly similar between prokaryotes and eukaryotes. The following is a description of elongation in prokaryotes.

1. Elongation proceeds after initiation with the binding of an aminoacyl-tRNA to the A site, which is the next codon in the mRNA. The aminoacyl-tRNA is brought to the ribosome through a series of interactions with EF-Tu (an elongation factor). This step involves the hydrolysis of GTP: EF-Tu-GTP --> EF-Tu-GDP (The hydrolyzed GDP is switched for GTP through another series of reactions with EF-Ts.)
2. The next aminoacyl-tRNA binds to the codon, and the C-terminus of the F-Met undergoes nucleophilic attack by the N-terminus of the second amino acid. The F-Met is now connected to the second amino acid through a peptide bond.
3. The first tRNA (for F-Met) is now uncharged. The entire ribosome complex moves along the mRNA through the action of another elongation factor (EF-G) and the hydrolysis of GTP --> GDP.
4. The first tRNA is now in the E site and comes off from the ribosome, while the second tRNA, with the nascent peptide chain, is in the P site. Step 1-4 will repeat as successive amino acids are added.

Elongation factors are a set of proteins that facilitate the events of translational elongation, the steps in protein synthesis from the formation of the first peptide bond to the formation of the last one. ... A peptide bond is a chemical bond that is formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). ...

Termination

Termination of protein biosynthesis occurs when the ribosome comes across a stop codon, for which there is no tRNA. At this point, protein biosynthesis halts and one of three release factors will bind to the stop codon. (Note: In eukaryotes, there is only one release factor that will bind to all three stop codons.) This induces a nucleophilic attack of the C-terminus of the nascent peptide by water - this hydrolysis releases the peptide from the ribosome. The ribosome, release factor, and uncharged tRNA then dissociate and translation is complete. RNA codons. ... The release factor is a protein that recognises the termination codon or stop codon in a mRNA sequence. ...

Events following protein translation

The events following biosynthesis include post-translational modification and protein folding. During and after synthesis, polypeptide chains often fold to assume, so called, native secondary and tertiary structures. This is known as protein folding. Posttranslational modification means the chemical modification of a protein after its translation. ... Protein before and after folding. ... A representation of the 3D structure of the myoglobin protein. ... In biochemistry and chemistry, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates. ... Protein before and after folding. ...

Many proteins undergo post-translational modification. This may include the formation of disulfide bridges or attachment of any of a number of biochemical functional groups, such as acetate, phosphate, various lipids and carbohydrates. Enzymes may also remove one or more amino acids from the leading (amino) end of the polypeptide chain, leaving a protein consisting of two polypeptide chains connected by disulfide bonds. A disulfide bond (SS-bond), also called a disulfide bridge, is a strong covalent bond between two sulfhydryl groups. ... In organic chemistry, functional groups (or moieties) are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ... An acetate, or ethanoate, is a salt or ester of acetic acid. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... Some common lipids. ... Lactose is a disaccharide found in milk. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ...

See also

• Genetic code
• Cistron
• Operon
• lac operon

For a non-technical introduction to the topic, see Introduction to Genetics. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... An operon is a group of key nucleotide sequences including an operator, a common promoter, and one or more structural genes that are controlled as a unit to produce messenger RNA (mRNA). ... The lac operon is an operon required for the transport and metabolism of lactose in Escherichia coli and some other enteric bacteria. ...

External links

• Science aid:Protein synthesis For high school
• Protein Synthesis
• Transcription

  Translation

• Protein Synthesis Animation Wesleyan University Learning Objects animation of protein synthesis.
• Interactive Java simulation of transcription initiation. From Center for Models of Life at the Niels Bohr Institute.
• From RNA to Protein Synthesis hypervideo.