Function of plasma membrane (endocytosis, Pinocytosis, junctions)

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FUNCTIONS OF PLASMA MEMBRANE

    PART-2 

CONTINUING FROM PART-1 

b) Endocytosis- It is of two types:-

      I) Phagocytosis- It is editing phenomenon where large particle like bacteria dead cell debris etc. are engulfed in by vesicle formed by plasma membrane. The vesicle is called phagosome. 

                Example-macrophages,kupffer cells in liver ,reticular cell in spleen ,histocytes in connective tissue, monocytes and neutrophils.

       II) Pinocytosis- It is the non specific uptake of small droplets of extracellular fluid by pinosome. It is a cell drinking phenomenon.

2) plasma membrane separates Protoplasm from external environment.

3) plasma membrane protect cell from injury.

4) plasma membrane forms sheat of cilia and flagella.

5) plasma membrane forms various types of in folding like:

   I) Microvillus:- It increases the surface area for absorption of digested food in small intestine and solutes in nephron.

  II) Mesosomes:-  It is found in Gram Positive Bacteria to perform molecular respiration.

  III)Lamelasome:- It is structurally and functionally similar to mesosome and found in blue green algae.

  IV)Lomasome:- It is in folding of plasma membrane in fungi which help in diffusion of substances during cell wall formation.

6) various type of junctions:-

     I) Tight Junction:- At this junction adjacent cell get fused. A protein band binds plasma membrane. 

                       Example:-  It is found in blood capillaries, collecting tubules and brain cells.

      II) Gap junctions:- At this junction adjacent cells have protoplasmic connections through special proteins called connexions.

                           Example:- Cardiac muscle cells.

        III) Desmosomes:- At this junctions , adjacent membrane possess disc shaped thickening.The disc possess tonofibrils.

                 Example:- Stratified squamous epithelia.

        IV) Terminal bar:- It is same to desmosomes but lack tonofibrils.

             

                 Example:- Stratified squamous epithelia.

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FUNCTION OF PLASMA MEMBRANE (ACTIVE TRANSPORT,PASSIVE TRANSPORT)

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FUNCTIONS OF PLASMA MEMBRANE

PART-1

1.The most important function of plasma membrane is transport of different substances into and out of the cell.

 

        Some types of transport:-

I) Passive transport- This type of transport do not require energy. It is 3 types:-

  a) Simple diffusion- Net movement of particles (Ions/Molecules) from any of their higher concentration towards an area of lower concentration that is along the concentration gradient.  

              Example- Movement of fats, oxygen, carbon dioxide and water to the Lipid portion of the membrane.

b) Osmosis- It is a diffusion of solvent molecules across a semipermeable membrane.

              Example- Movement of water into and out of the cell membrane.

c) Facilitated diffusion-Transport of particles is facilitated by some carrier protein e.g., permeases or translocases. Carrier protein bind to the substances with stereochemical specificity so highly selective.

            Example-Entry of glucose into RBC by D-hexose permease , entry of water through aquaporins in plasma membrane of cell.

II) Active transport-This type of transport require ATP. Movement of a particle against the concentration gradient by some carrier protein.

             Example- movement of most ions and amino acids by Na+-K+ ATPase , calcium ATPase, Proton pump.

III) Bulk transport- this type of transport figure ATP. It occurs with the help of vesicles. It is of three types- 

a) Exocytosis-secretion or ejection of particles from form a cell, particles being enclosed in a vesicle which fuses with the plasma membrane and release the content outside the cell.

                Example-secretions of neurotransmitter, hormones, mucus etc , ejection of cell waste.

REMAINING PART TOMORROW..... THANK YOU FOR READING.

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