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Plasma Membrane

The biological membrane, which is present in both eukaryotic and prokaryotic cell. It is also called as cell membrane as it is works as a barrier between the inner and outer surface of a cell. In animal cells, the plasma membrane is present in the outer most layer of the cell and in plant cell it is present just beneath the cell wall.

Structure of Plasma Membrane

Plasma Membrane


Plasma Membrane Definition

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Plasma membrane can be defined as a biological membrane or an outer membrane of a cell, which is composed of two layers of phospholipids and embedded with proteins. It is a thin semi permeable membrane layer, which surrounds the cytoplasm and other constituents of the cell.

Function of Plasma Membrane

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  1. It separates the contents of the cell from its outside environment and it regulates what enters and exits the cell.
  2. Plasma membrane plays a vital role in protecting the integrity of the interior of the cell by allowing only selected substances into the cell and keeping other substances out.
  3. It also serves as a base of attachment for the cytoskeleton in some organisms and the cell wall in others. Thus the cell membrane supports the cell and helps in maintaining the shape of the cell.
  4. The cell membrane is primarily composed of proteins and lipids. While lipids help to give membranes their flexibility and proteins monitor and maintain the cell's chemical climate and assist in the transfer of molecules across the membrane.
  5. The lipid bilayer is semi-permeable, which allows only selected molecules to diffuse across the membrane.

Characteristics of Plasma Membrane

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Below you could see characteristics of plasma membrane

  1. The plasma membrane (cell membrane) is made of two layers of phospholipids. 
  2. The plasma membrane has many proteins embedded in it.
  3. The plasma membrane regulates the entry and exit of the cell. Many molecules cross the cell membrane by diffusion and osmosis.
  4. The fundamental structure of the membrane is phospho lipid bilayer and it forms a stable barrier between two aqueous compartments.
  5. The proteins present in the plasma membrane, act as pumps, channels, receptors, enzymes or structural components.

Plasma Membrane Structure

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  1. It is the boundary, which separates the living cell from their non-living surroundings.
  2. It is the phospholipids bilayer.
  3. Plasma membrane is an amphipathic, which contains both hydrophilic heads and hydrophobic tails.
  4. It is a fluid mosaic of lipids, proteins and carbohydrate.
  5. It is lipid bilayer, which contains -two layers of phospholipids, phosphate head is polar (water loving), fatty acid tails non-polar (water fearing) and  the proteins embedded in membrane.
Plasma Membrane Structure

Plasma Membrane Structure

Components of Plasma Membrane

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The main components of plasma membrane include:
  1. Proteins like glycoprotein, which are used for cell recognition and act as receptors and antigens. 
  2. Proteins like glycolipids are attached to phospholipids along with the sugar chains.
  3. Lipids with short chain of carbohydrates are attached on the extracellular side of the membrane.
  4. Phospholipid Bilayer - which are made up of phosphates and lipids. They create a partially permeable membrane, which allows only certain substances to diffuse through the membrane.
  5. Cholesterol – it maintains the fluidity of cell surface membrane.
Components of Plasma Membrane

Components of Plasma Membrane

Proteins in Plasma Membrane

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In plasma membrane, a protein helps in providing the support and shape to the cell. There are three types of proteins in plasma membrane, which includes:

  1. Cell membrane receptor proteins- It helps in communication of a cell with their external environment with the help of hormones, neurotransmitters and other signaling molecules.
  2. Transport proteins - It helps in transporting molecules across cell membranes through facilitated diffusion. For example: globular proteins.
  3. Glycoprotein - It helps in cell to cell communications and molecule transport across the membrane.

Prokaryotic Plasma Membrane

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The prokaryotic plasma membranes are composed of phospholipids bilayer with embedded proteins. In the middle of the bilayer, the fatty acids of the phospholipids are found, which is called as hydrophobic region. Prokaryotic cells can have multiple plasma membranes. In prokaryotic organisms, plasma membranes are responsible for controlling the entry and exit of the cell.

Eukaryotic Plasma Membrane

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The eukaryotic plasma membrane is a phospholipids bilayer containing proteins and carbohydrates attached to the proteins and sterols. It is a fluid phospholipids bilayer embedded with proteins and glycoprotein. The phospholipids bilayer is arranged in such a manner that they form the center of the membrane. They also contain sterols, which makes the membrane less permeable and helps to stabilize the membrane and add the rigidity to membranes.
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