Structure and functions of plasma membrane

1. PLASMA MEMBRANE
STRUCTURE & FUNCTION
PRESENTED BY,
AKSHAYA ANIL
S 3 M Sc BIOCHEMISTRY
DEPT.OF BIOCHEMISTRY
KERALA UNIVERSITY 1

2. PLASMA MEMBRANE
 Thin,fragile
 5 – 10 ꞃm wide
 Lipid bilayer
 Polar head & nonpolar tail
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Around 5000
plasma membrane
stacked one above the
other is equal to the
thickness of a single
page of the book…

3. HISTORY
 Ernest Overton(1890)
Chemical nature of outer boundary layer of the cell
 E.Gorter & F.Grendel(1920-1930)
Proposed the biological membranes consists of bilayer
 Hugh Davson James & James Danielli(1935)
Proposed lipid bilayer was lined on both sides inner & outer
by a layer of globular cells
 S.Jonathan Singer & Garth Nicolson(1972)
Prosposed fluid mosaic fluid 3

4. • Central dogma of membrane biology
• The structure and arrangement of membrane proteins occurs as
a “mosaic” of discontinous particles that penetrate the lipid
sheet
• Protraits cell membranes as dynamic structures
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5. • Membranes are lipid protein assemblies held together by non
covalent bonds
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LIPIDS
•Phospholipids
Glycerophospholipids
Sphingolipids
•Sterol Cholesterol
CARBOHYDRATES
•Glycolipids
•Glycoproteins
PROTEINS
•Integral
•Peripheral
•Lipid anchored

6. 6
• Core membrane consists of a sheet of lipids
arranged in a bimolecular layer
• Lipid bilayer,structural backbone provides
barrier that prevents random movement of
water-soluble materials into & out the cell
• Protein part perform the specialized functions
of the cell

7. • Contain a wide diversity of lipids
• Amphipathic
PHOSPHOLIPIDS
SPINGOLIPIDS
CHOLESTEROL
MEMBRANE LIPIDS
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8. LIPID MOLE PERCENT
PHOSPHATIDYLCHOLINE 20
PHOSPHATIDYLETHANOLAMINE 11
PHOSPHATIDYLSERINE 4
PHOSPHATIDYLINOSITOL 2
CHOLESTEROL 49
SPINGOMYELIN 13
GLYCOLIPIDS 1
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9. • Most membrane lipids contains a phosphate group which them
phospholipids
• Phospholipids are built on glycerol backbone,so called
phosphoglycerides
• Membrane glycerides are diglycerides,only two hydroxyl group are
esterified to fatty acid
• 3rd group is esterified to a hydrophilic phosphate group
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10. • Additional groups attached with phosphoglycerides are
small & hydrophilic
• Together with the negatively charged phosphate group
to which it is attached forms a highly water soluble
domain called the head group
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11. • Fatty acid chains are hydrophobic, unbranced
hydrocarbons ~16-22 carbons in length
Saturated
Monounsaturated
Polyunsaturated
Membrane fattyacids
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12. • Less abundant class
• Derivative of sphingosine
• Sphingosine is a amino alcohol that contains a long
hydrocarbon chain attached by its amino group
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13. • Animal cell constitute upto 50%lipid molecules in the
membranes
• Plant cells contains cholesterol like sterols
• Cholesterol molecules are oriented with their small
hydrophilic hydroxyl group towards the membrane surface &
the remainder of the molecule embedded in the lipid bilayer
• The hydrophobic rings of a cholesterol molecule are flat &
rigid & it interfere with the movements of fattyacid tails of
the phospholipids.
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14. 14
LIPID HUMAN RBC HUMAN MYELIN E.COLI
PHOSPHATIDIC ACID 1.5 0.5 0
PHOSPHATIDYLCHOLINE 19 10 0
PHOSPHATIDYLETHANOL
AMINE
18 20 65
PHOSPHATIDYLGLYCEROL 0 0 18
PHOSPHATIDYLSERINE 8.5 8.5 0
GLYCOLIPIDS 10 26 0
SPINGOMYELIN 17.5 8.5 0
CHOLESTEROL 25 26 0

15. • Depending upon species carbohydrate content ranges
between 2-10 %
• More than 90% of the membrane’s carbohydrate is
linked to proteins to form glycoproteins
• Remaining is covalently linked to lipids to form
glycolipid
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16. • Present as short , branched hydrophilic oligosaccharides
• Oligosaccharides may attached to the amino acid by
• Play a major role in mediating the interactions of cell
• Involved in the sorting of membrane proteins to different
cellular compartments
• ABO blood grouping
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N – glycosidic linkage
O- glycosidic linkage

17. • Depending on the cell type & the particular organelle within
that cell,a membrane may contain 100s of proteins
• Membrane proteins are grouped into 3
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INTEGRAL PROTEINS
PERIPHERAL PROTEINS
LIPID ANCHORED PROTEIN
MEMBRANE
PROTEINS

18. • Penetrate the lipid bilayer
• Transmembrane proteins
• Have domains that protrude from both the extracellular &
cytoplasmic sides of the membrane
• Some have only one membrane spanning domain,some have
multispanning
• Constitute 25-30 % of all encoded proteins
• Roughly 60% are drug targets
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19. • Located entirely outside the lipid bilayer
• Either the cytoplasmic or extracellular side
• Associated with the surface of the membrane by non covalent
bonds
• Provide mechanical support for the membrane
• Act as an anchor for the integral membrane proteins
• On the internal plasma membrane surface function as
enzymes,specialised coats,or factors that transmit
transmembrane signals
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20. • Located outside the lipid bilayer
• Either on the extracellular or cytoplasmic surface
• Are covalently linked to a lipid molecule that is situated
within the lipid bilayer
• Peripheral membrane proteins linked to phosphoinositol
embedded in the outerleaflet of lipid bilayer by a
small,complex olidosaccharide are called GPI anchored
protein
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21. COMPARTMENTALISATION
SCAFFOLD BIOCHEMICAL ACTIVITIES
PROVIDING A SELECTIVELY PERMEABLE MEMBRANE
TRANSPORTING SOLUTES
RESPONDING TO EXTERNAL STIMULI
INTERCELLULAR INTERACTIONS
ENERGY TRANSDUCTION
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22. REFERENCES
• Cell Biology,Gerald Karp,7th edition
• The Cell,a molecular approach,Geoffrey M.Copper &
Robert e.Hausmann,7th edition
• Lehninger Principles of Biochemistry,David L.Nelson
& Michael M. Cox,7th edition
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