What is Cell Membrane | Functions of Cell Membrane

Definitions of Cell Membrane:
All living cells and many of the tiny organelles are bounded by thin, tough and elastic limiting membranes called cell membrane. It acts as a selective barrier that separates the interior of a cell from its surroundings or outside environment. This outer boundary or selective barrier of the cell is also called the plasma membrane. 
Cell membrane
Fig: Cell membrane
What is Fluid Mosaic Model?
The fluid mosaic model describes the cell membrane as a tapestry of several types of molecules or components including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character. The ‘Fluid’ part explains how some parts of the membrane can move around freely, if they are not attached to other parts of the cell. The ‘mosaic’ part represents the ‘patchwork’ of proteins that is found in the Phospholipid Bilayer.

They are attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane that are constantly moving. This movement assists the cell membrane keep its role as a barrier between the inside and outside of the cell environments.

Composition of Cell Membrane:
All the compositions of cell membrane have pointed out in the below with their percentage:
  • Protein: 55%,
  • Lipid: 42%,
  • Phospholipid: 25%,
  • Cholesterol: 13%,
  • Other lipids: 4%,
  • Carbohydrates: 3%.
Main Functions of Cell Membrane:
All the functions of cell membrane have listed in the following:
  1. It helps to maintain the shape and size of the cell.
  2. Separate the intracellular components from the extracellular environment.
  3. It separates and retains one cell cytoplasm from another neighboring cell (act as boundary).
  4. Proteins like glycoprotein, which are used for cell recognition and act as receptors and antigens.
  5. Phospholipid Bilayer creates a partially permeable membrane, which allows only certain substances to diffuse through the membrane.
  6. Cholesterol it maintains the fluidity of cell surface membrane.
  7. Endocytosis: cell membrane transports large molecules (or even whole cells) by engulfing them.
  8. Exocytosis: cell membrane removes or secretes substances such as hormones or enzymes.
  9. Cell membrane participates in the process of antibody.
  10. It removes or secretes substances such as hormones or enzymes.
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