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The cell membrane is the external cover of the living cells that regulates what goes in and out of the living cell. Not to be confused with Cell wall

Cell membrane is said to be semi-permeable because it inhibits the entry of certain substances while permitting some and vice versa.

Structure of the cell membrane

The cell membrane is mainly composed of the following:

  1. Phospholipids bilayer
  2. Cholesterol
  3. Proteins

Phospholipids bilayer

The phospholipid components of the cell membrane look like a balloon with two strings. It is made up of three parts: phosphate group head, glycerol backbone and two fatty acid tails.

The phospholipid bilayer looks like a balloon with two strings. The phosphate head is hydrophilic (water loving), the fatty acid tail is hydrophobic (water hating) while the glycerol backbone glues the phosphate head and the fatty acid tail together. Thus making cell membrane amphipathic (for it contains both the water loving and water hating component).


High level of Cholesterol is notorious for its role in clogging arteries and thus contributing to heart disease and stroke. But cholesterol is essential to the body, too. It is an important component in cell membranes, and the body uses cholesterol in making sex hormones, adrenal hormones, and vitamin D. When the temperature of the environment increases, cholesterol goes in between the phospholipid bilayer to keep them from over-fluidity and from being packed together in cold temperature.


Two proteins commonly found in the cell membrane are the peripheral and integral proteins. The peripheral proteins are present on the phospholipid bilayer on the cell membrane acting as enzymes or hormone while the integral proteins lie between the phospholipid bilayers and permits the inward and outward movement of substances in and out of the cell and as well serve as receptor site for external molecules example is G-protein coupled receptor.

However, some glycoproteins (Carborhydrates linked with protein) and glycolipids (Carbohydrates linked chemically with lipids) exists in the the cell membrane.



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