Biology Reference
In-Depth Information
in water are called membrane proteins (or integral proteins). Membranes
are semi-permeable and are involved in a vast array of cellular processes
such as cell adhesion, ion channels, and transport of small molecules.
The most important feature of a biomembrane is that it has a selective
permeability to ions and molecules. This means that the size, charge and
other chemical properties of the ions or molecules attempting to cross the
biomembrane will determine whether they succeed to do so. Such selective
permeability is essential for effective separation of a cell or organelle from
its surroundings. Viruses are too large and are unable to cross the membrane
by themselves; in such cases transport into the cell depends on endocytosis.
In general, explaining how the membrane proteins are involved in the
organization and function of any membranes requires knowing their
molecular structures. The tertiary structures of the P2 basic protein of PNS
myelin (bovine, 1PMP; equine, 1YIV), the soluble part of P0 protein (rat,
recombinant, 1NEU) and the soluble part of MOG (mouse, recombinant
1PY9) are known. The three-dimensional structures of other (and full
sequence) myelin membrane proteins are not yet known.
Biological Membranes — Protein/Lipid Ratio
There are no biological membranes which are made up 100% of lipids or
100% of proteins. For all known membranes the ratio of proteins to lipids
(w/w) is in the range 1:3 to 3:1. This is summarized in Table 1.
One of the most lipid-rich membranes is the myelin membrane: 75%
by weight are lipids. In contrast, the purple membrane contains only 25%
lipids by weight.
Whether such large differences in the lipid to protein ratio can directly
affect the structure of membrane proteins is not known, but might be an
interesting area of future study.
Basic Bioinformatics
At present, membrane-protein bioinformatics predictors perform
quite well on two tasks: identifying membrane-protein encoding genes
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