2. What is cell membrane?
Cell membrane is a dynamic biological
membrane ,it can physically seperate cytoplasm
from surrounding and cell from outside the
environment .
It is encloses every type of cell both
Prokaryotes and Eukaryotes.
Cell membrane term coined by C.Nageli and C.
Cramer (1855)
Its also known as , Cytoplasmic membrane
(OR) plasma lemma or plasma membrane.
3. It is fluid mosaic assembly of molecules ‘composed with
lipids,proteins ,carbohydates and enzymes.
It looks like “Sea of Lipids and Proteins are float like
ship”.
To study physical and chemical composition ,RBC cells
are widely used through hemolysis process(done
by:E.Gorten and F. Grendal.
4. LIPIDS
Lipids are major components in plasma
memebrane ,they are glycerolipids,
phospholipds,sphingolipids and
sterols(cholesterol)
5. CHEMICAL COMPOSTION
Composed of proteins lipids and carbohydrates.
The human plasma membrane contains
52% of protein,48%of lipid, 8%of carbohydrate.
In bacteria ,70%of protein
30%lipid,<1%carbohydrate.
Species &
tissue
Protein(%) Lipids(%) Carbohydra
tes(%)
Human-CNS
Myelin
20 79 3
Bovine –PNS
myelin
23 76 8
Rat muscle 65 35 5
Human
Erythrocyte
60 40 80
7. CHOLESTEROL
Found in dipressed between the
hydrophobic tails of the
phospholipds
It regulates the fluidity of the
membrane
Lipid rafts : Functional unit of cell
membrane
LIPID RAFTS
8. Main component of cell membranes. Those
are important for structure and transport
of ion channels
Based on position ,two types:
protein
Integral/Intrinsic Peripheral/Extrinsic
PROTEINS
9. INTEGRAL/INTRINSIC PROTEIN
This protein will binds with proteins or integrates with
proteins
Insoluble in water(hydrophobic)
Eg:Glycophorin,Band-3,GPCR
Glycophorin:
3-4 glycophorins present in membrane
mol wt. 55,000 Da(60% carbohydrtes)
CooH end of molecule interacts with lipids of
membrane(hydrophobic)
NH2 end exposed to external environment
attached to oligosaccharides outside the membrane
they contains antigenic determinants
Eg:Human RBC :5,00,000 copies of Glycophorins
10. PERIPHERAL PROTEINS
Free of lipids, soluble in aqeous(hydrophillic)
all the proteins are primarily synthesized in
ribosomes(ER) processed in golgi and
transferred to plasma membrane.
11. ENZYMES OF MEMBRANE
1. >30 enzymes are symmetrically distributed in
the plasma membrane.
2. Most commonly found enzymes,
1. Acetyl phosphatase
2. Acetyl
cholinesterase
3. Acid phosphatase
4. Adenosine
triphosphatase
5. Mg2+ ATPase
6. Na+ _ K+ ATPase
7. RNAase
8. Alkaline
phosphatase
9. Aminopeptidase
10. Cholestrol esterase
1. 11.Guanylase
cyclase
2. Monoglyceride lipase
3. NAD-ase
(Ectoenzyme of
erythrocyte)
4. Protein kinase
(Endoenzyme of
erythrocyte)
5. Protein
kinase(Endoenzyme
of erythrocyte)
6. Phospholipase A
7. Lactase
8. Maltase
9. Sialidase
12. CARBOHYDRATES
Short ,unbranched ,chain sugars
(oligosaccharides)
Mainly two types,
Glycolipids:
which bind to phosphilipids
Glycoproteins:
which binds to proteins of
membrane
13. FUNCTIONS OF PLASMA MEMBRANE
Gives Mechanical protection to the cell.
Acts as permeability barrier
Protects the cell content
For transport and signal transduction ,cell-cell
interactions and enzymatic functions
Antigenic specificities located at plasma
membrane
14. MODELS OF PLASMA
MEMBRANE
Sandwich model/tri lamellar model
In 1935 Danielli and Davson studied triglycerlide
bilayer over water surface
In this model, biomolecular layer of lipid in
(sandwich) b/w two single layer of proteins
15. Unit membrane model:
In 1965, Robertson noted the structure seen in
electron microscope.
Acc to this all the cellular and organelle are
structural and functionally similar.
Those models are rejected because, they failed
to explain the permeability.
Later in 1972 Jonathan singer and Nicolson
proposed fluid mosaic model.
16. FLUID MOSAIC MODEL
It is widely accepted model, plasma membrane
made by lipid bilayer
17.
18. REFERENCES
Cell biology by (SS Rastogy).
Cell and,Molecular biology by (2006) De
Roberties and De Roberties jr.
Cell and,Molecular biology ,Dr.Ps Varma, and
agarwal, (Publisher: S Chand).
Slidershare net.
