with carbohydrate groups attached to lipids, glycolipids, or proteins, glycoproteins. These short
carbohydrates, or oligosaccharides, are usually chains of 15 or fewer sugar molecules.
Oligosaccharides give a cell identity (i.e., distinguishing self from non-self) and are the
distinguishing factor in human blood types and transplant rejection. A very significant chemical
fact about membranes is that the relative proportion of protein differs greatly from lipids, ranging
from 20% protein in the case of neuronal myelin membranes to 75% protein for the inner
membrane of mitochondria [18].
Figure 1-1: A molecular view of the cell membrane0F
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1.3.1
31BLipids
Lipids may be broadly defined as hydrophobic or amphiphilic small molecules. In most
membranes, approximately 40%-50% of the mass of the membrane is composed of lipids. Lipids
provide a matrix for protein groups, acts as a barrier for ions & molecules and have the same
structure in all membranes. Lipids are a diverse group of large biological molecules that do not
include polymers and is made up primarily or exclusively of non-polar groups. They are grouped
together and have little or no affinity for water. Due to their non-polar character, lipids typically
dissolve more readily in non-polar solvents such as acetone, ether, and benzene etc. This
solubility characteristic is of extreme importance in cells because lipids act as barriers and form
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