Download Membrane Carbohydrates

Membrane Carbohydrates
The extracellular surface of the cell membrane is decorated with
carbohydrate groups attached to lipids and proteins. Carbohydrates are
added to lipids and proteins by a process called glycosylation, and are
called glycolipids or 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
"nonself") and are the distinguishing factor in human blood types and
transplant rejection.
The Distribution of Membrane Carbohydrates is
Asymmetric
As discussed above and seen in the picture, the distribution of
carbohydrates in the cell membrane is asymmetric. The extracellular
face of the membrane, which is in contact with the extracellular fluid.
The extracellular side of the membrane contains oligosaccharides that
distinguish the cell as "self." It also contains the end of integral proteins
that interact with signals from other cells and sense the extracellular
environment. The inner membrane is in contact with the contents of the
cell and tends to have few carbohydrates. Instead, this intracellular side
of the membrane anchors to the cytoskeleton and contains the end of
integral proteins that relay signals received on the external side.
Summary: Membranes as Mosaics of Structure and
Function
The biological membrane is a collage of many different proteins
embedded in the fluid matrix of the lipid bilayer. The lipid bilayer is the
main fabric of the membrane, and its structure creates a semipermeable
membrane. The hydrophobic core impedes the diffusion of hydrophilic
structures such as ions and polar molecules, but allows hydrophobic
molecules, which can dissolve in the membrane, to cross it with ease.