Porins are transmembrane proteins that are large enough to facilitate passive diffusion. They are prevalent in the outer membrane of the mitochondria and Gram-negative bacteria. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Diffusion, being the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ...

Porins are almost entirely composed of beta sheets and control the diffusion of small metabolites like sugars, ions, and amino acids. Although the inner membrane is a major permeability barrier, the outer membrane contains porin which renders it largely largely permeable to molecules less than about 1500 daltons. Diagram of Β-Pleated sheet and bond structure of protein The β sheet (also β-pleated sheet) is a commonly occurring form of regular secondary structure in proteins, first proposed by Linus Pauling and Robert Corey in 1951. ... This article deals with sugar as food and as an important, widely traded commodity; the word also has other uses; see Sugar (disambiguation) A sugar is a form of carbohydrate; the most commonly used sugar is a white crystalline solid, sucrose; used to alter the flavor and properties (mouthfeel, perservation... An ion is an atom or group of atoms with a net electric charge. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ...

References

• The human beta barrel porin protein

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