3. Apart from membrane-lipids and membrane-proteins, the final basic component of a biomembrane is membrane-carbohydrates. However, they do not exist in isolation, rather in combination with membrane-lipids to form glucolipids/glycolipids, or combine with membrane-proteins to form glucoproteins/glycoproteins. The combination happens via covalent bonds.

Membrane-Lipids and -Proteins. Click on image for credit.

Most membrane carbohydrates are located on plasma membranes and have the following functions:

  • Improve the stability of membranes.
  • Advance the fastness and activate proteinase (protein enzymes which hydrolyze proteins into polypeptides) in the extracellular matrix.
  • Help membrane-proteins form correct three-dimensional configurations.
  • Take part in cell signal recognition, cell adhesion and cell junction (more detail later).
  • Correct the position and orientation of new proteins for transfer.
  • Lectin, a glucoprotein, protects the cell. So they also aid in protection.
  • Glucolipids act as blood groups determinants because some function as cell recognition particles.

I understand that stating these important roles is not enough to fully comprehend their significance. Later chapters will deal with the details. This is simply a fleeting reference to their roles.

In general, according to their main functions proteins and glycoproteins can be classified to five types:

  1. Channel proteins to form pores for the free transport of small molecules and ions across the membrane (more in Chapter 4).
  2. Carrier proteins to facilitate diffusion and active transport of molecules and ions across the membrane (more in next post).
  3. Cell Recognition Proteins; identifies a particular cell or gives them identity (more in Chapter 7).
  4. Receptor proteins; binds with specific molecules such as hormones and cytokines and gets activated to perform a specific function (also more in chapter 7).
  5. Enzymatic proteins; catalyze specific chemical reactions.
I think it is becoming clear that proteins are really important macro molecules and that most of animal cell biology will discuss it’s various functions.
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