STRUCTURE OF CELL MEMBRANE:
1) Cell membrane is composed of phospholipids and proteins.
2) It has double layer of molecules (lipid bilayer)which are amphiphatic in nature.
3) The hydrophobic component is placed towards centre and hydrophilic component away from centre.
4) The outer flap(layer) of cell membrane mainly has phosphatidyl choline and sphingomyelins whereas inner flap have phosphatidyl ehtanuolamine and phosphatidyl serine.
5) Inbetween the lipids there are some cholstreol molecules which have hydroxyl gruops lieing outwards.
6) There are many protiens,channels, receptors embedded in the cell membrane like peripheral protiens ,integral protiens,receptor protiens etc...
7) Lipid soluble substances can easily pass through the membrane because the core of the membrane is composed of lipids.
8) Water soluble substances, polar molecules , molecules of large size cannot pass easily so they require speacial transport mechanisms to pass through.
#PROTIENS PRESENT IN CELL MEMBRANE :
* Mainly of two types:
1) INTEGRAL PROTEINS /TRANS MEMBRANE PROTEINS:
* Theses proteins pass through the membrane.
* They are tightly attached by covalent bonds.
* Examples are ion channels ,carrier proteins etc...
2) PERIPHERAL PROTEINS :
* These proteins are generally attached either outside or inside of the membrane.
* They are loosely attached to the membrane.
* Their main function is to act as cytoskeleton and as secondary messengers.
#COMPOSITION OF CELL MEMBRANE:
Protein content -50%
Lipids content - 47%
Carbohydrates -3%
# FLUIDITY OF CELL MEMBRANE:
* The lateral movement of phospholipids and cholesterol molecules is called as fluidity of cell membrane.
* Due to fluidity cell membrane can exhibit exocytosis , endocytosis , and biogenesis of cell membrane .
# FACTORS AFFECTING FLUIDITY OF CELL MEMBRANE :
1) Temperature :
* As temperature increases fluidity increases.
2) Cholesterol concentration :
* As cholesterol increases , fluidity decreases.
3) Saturation of fatty acids :
* More the saturation less will be fluidity .
* Presense of unsaturated fatty acids increases fluidity .
#FUNCTIONS OF CELL MEMBRANE:
1) Separates external environment from internal environment.
2) Allows selective permeability of various substances.(various transport mechanisms)
3) Maintains shape of the cell
4) Helps in enzymatic activity by having many receptors .
5) Helps in cell recognition.
#SPECIALISED FEATURES OF CELL MEMBRANE:
1) LIPID RAFTS
* special area within cell membrane where the membrane is tightly packed and have saturated fatty acids loaded with cholesterol in between.
* They have receptors passing through them (example:seven pass receptors like epinephrine receptors)
2) CAVEOLAE:
* These are the flask shape depressions in the plasma membrane present in many cells like endothelial cells,smooth muscle cells etc..
* They are useful im signal transduction,mechano protection, endocytosis and exocytosis.
# FLUID MOSAIC MODEL OF CELL MEMBRANE :
1) Proposed by G.L.Nicolson and S.J.Singer in 1972.
2) It tells that cell membrane is lipid bilayer and protiens embedded in between.
3) Lipid bilayer provides fluidity (lateral movement) to the membrane.
4) The hydrophilic component is towards the aqueous environment and hydrophobic component towards the centre.
5) Thickness of cell membrane is about 5nm to 10nm.
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