The plasma membrane is a thin, fragile lipid bilayer 5-10 nanometers wide that forms the outer boundary of cells. It is composed of phospholipids with hydrophilic head groups and hydrophobic fatty acid tails that form a bilayer. Embedded within this bilayer are proteins and cholesterol that give the membrane fluidity and allow it to perform specialized functions like transport and responding to stimuli. The plasma membrane plays an essential role in compartmentalizing the cell and regulating what enters and exits.

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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