The cell membrane is a thin semi-permeable membrane that surrounds the cytoplasm of a cell,
enclosing its contents. This biological membrane controls the movement of substances in and
out of the cell.
The definition of cell membrane is a thin semi-permeable membrane that surrounds the
cytoplasm of a cell, enclosing its contents.
This picture shows two cells, and the plasma membrane are the two lines.
Each line belongs to different cell. So they are distributed in the intercelular space separate
Cell membranes contain a variety of biological molecules, notably lipids and proteins. Material is
incorporated into the membrane, or deleted from it, by a variety of mechanisms.
- Fusion of intracellular vesicles with the membrane (exocytosis) not only excretes the
contents of the vesicle but also incorporates the vesicle membrane's components into the
cell membrane. The membrane may form blebs around extracellular material that pinch off to
become vesicles (endocytosis).
- When the membrane has a tubular structure, the material from the tube can be drawn into the
- Although the concentration of membrane components in the aqueous phase is low (stable
membrane components have low solubility in water), there is an exchange of molecules
between the lipid and aqueous phases.
The picture shows one of the mechanisms to incorporated material into the cell.
The cell membrane consists of three classes of amphipathic lipids: phospholipids, glycolipids,
The amount of each depends upon the type of cell, but in the majority of cases phospholipids
are the most abundant. 30% of the plasma membrane is lipid.
● Phospholipids are a class of lipids that are a major component of all cell membranes
as they can form lipid bilayers. The 'head' is hydrophilic (attracted to water), while the
hydrophobic 'tails' are repelled by water and are forced to aggregate.
● Glycolipids are lipids with a carbohydrate attached. Their role is to provide energy and
also serve as markers for cellular recognition. There are in the external monocape but
there aren't very normally in animal cell.
● Cholesterol is an organic chemical substance classified as a waxy steroid of fat. It is
the principal sterol synthesized by animals, predominantly in the liver; however, small
quantities can be synthesized in other eukaryotes such as plants and fungi. It is almost
completely absent among prokaryotes, i.e. bacteria.
It is an essential structural component of mammalian cell membranes and is required
to establish proper membrane permeability and fluidity. In addition, cholesterol is an
important component for the manufacture of bile acids, steroid hormones, and vitamin D.
Although cholesterol is important and necessary for the aforementioned biological
processes, high levels of cholesterol in the blood have been linked to damage to arteries