Question

What is the lipid composition of a normal human cell’s plasma membrane (choose a cell type)? Describe and draw, in detail, the chemical structure of a lipid from your choice.

Answer 1

Lipids in plasma membranes control localization and interactions of proteins involved in cell signal propagation. The components of the plasma membrane are mainly lipids (phospholipids and cholesterol), proteins, and carbohydrate groups that are attached to some of the lipids and proteins. The proportions of these components vary between different types of cells.

For a typical human cell, however, proteins account for about 50% of the composition by mass, lipids (of all types) account for ~ 40%, and the remaining 10% comprises of carbohydrates. If we talk about the lipid composition of specific cells like in erythrocytes, the general molar ratio of cholesterol to phospholipid in the erythrocyte membrane is about 0.8-0.9.

Fatty acids are the simplest form of lipids. A phospholipid is an amphipathic molecule with fatty acids, a platform (maybe glycerol or sphingosine) to which fatty acids are attached, phosphate and an alcohol attached to the phosphate. Phospholipids derived from glycerol are known as phosphoglycerides/glycerophospholipids. The simplest phosphoglyceride is phosphatidic acid with just hydrogen in place of X.

Phospholipids derived from sphingosine are known as sphingophospholipids. It has a carbon amino alcohol called sphingosine instead of glycerol. If X is H (simplest form), it becomes ceramide.

Lipids containing saccharide groups are known as glycolipids. A glycosphingolipid, a type of glycolipid is a major class of membrane lipids.