The document discusses the biological membrane and its chemical composition. It notes that the plasma membrane is the outer boundary of cells, consisting of a double layer of lipid molecules with embedded proteins. The major components of membranes are glycerophospholipids, sphingolipids, and cholesterol. Glycerophospholipids are amphipathic lipids that form the lipid bilayer structure. The fluid mosaic model describes membranes as a fluid structure with lipids and proteins able to move laterally. Membrane proteins can be integral or peripheral, and help with cell functions like transport and signaling. Membrane fluidity is influenced by temperature and lipid composition.

1. BIOLOGICAL MEMBRANE
&
ITS CHEMICAL COMPOSITION
PRADEEP SINGH, MANSI MODI
M.Sc. MEDICAL BIOCHEMISTRY
HIMSR, JAMIA HAMDARD

2. INTRODUCTION
Fundamental unit of life.
Self replicating structure.
The first cells were observed and named by Robert
Hooke in 1665 from slice of cork.
Cell membrane is a protective sheath, also known as
plasma membrane.
The region of cell lying between the plasma
membrane and the nucleus is the cytoplasm.

3. CONTENTS
• Plasma Membrane and its Functions
• Chemical Composition Of Membranes
• Lipids Bilayer and Micelles
• Mobility of Lipid Components In Membrane
• Fluid Mosaic Model
• Asymmetry Of Lipid Bilayer
• Membrane Proteins
• Fluidity Of Lipid Bilayer
• Lipid Rafts
• Dynamic Nature Of Membranes

4. Plasma Membrane
 Plasma Membrane of a eukaryotic cells is a dynamic, fluid
structure
 It forms the external boundaries of cell.
 All membranes consist of a double layer of lipid molecules in
which proteins are embedded.
 Thickness of cell membrane varies from 75-110Å
 STRUCTURE.

5.  FUNCTION’S
• Protective:-Forms outermost boundary of the cell organelles.
• Digestive:-Takes in food and excretes waste products.
• Selective Permeability:-
a)Non-Polar Molecules( gases like O2,CO2,N2,lipids, steroid hormones,
alcohol) can dissolve in the polar region of the membrane and move rapidly
across the membrane.
b) Polar molecules(Water soluble substances: ions, glucose, urea etc) have
much lower solubility , Therefore, penetrate the membrane much more slowly.
• Chemical and Physical Properties of membrane control the free
passage of ions in and out of cell. This property helps in maintaining components
in intracellular fluid and extracellular fluid.
• Insulating Properties:- It acts as dielectric material of a charged
condenser, thus cell membrane has a very high insulating value.

6. Chemical Composition Of Plasma
Membrane
• Plasma membrane have –54% lipids
46%protein
5-10%carbohydrates

7. Chemical Composition Of Plasma
Membrane
• Lipids and proteins are the two major components of
all membrane.
• Carbohydrates are present in outer leaflets.
• But in inner leaflets, do not have a significant role.
• Carbohydrates bound either to proteins as constituents
of glycoproteins , Or bound to lipids as constituents of
glycolipids.

8. Lipids Are The Major Components:-
• 3 major components of eukaryotic
membrane are
glycerophospholipids sphingolipids cholesterol

9. Glycerophospholipids
• Glycerophospholipids have a glycerol
molecule with a phosphate esterified at
the ɑ-carbon.
• And two long chain fatty acids esterifies
to the remaining carbon atoms.
• Structure of major alcohols esterified to
phosphatidic acid to form the
glycerophosphospholipid.
• For ex:-if alcohol is choline ,molecules is
called phosphotidylcholine and if serine,
then is called phosphotidylserine.

10. Glycerophospholipids
• Glycerophospholipids contain two
fatty acyl groups esterified to C1 and
C2 of glycerol.
• A saturated fatty acid is usually found
on C1 and unsaturated fatty acid on
C2.
• The presence of unsaturated fatty
acids has a marked effect on the
fluidity of the membrane.
• Phosphotidylcholine and
phosphotidylethanolamine are the
most common glycerophospholipids.

11. Glycerophospholipids
• Ether phospholipids contain an alkyl group
(alkyl acyl glycerophospholipid) termed as
plasmogens.
• Plasmogens containing ethanolamine or
choline plasmogens esterified to the
phosphate are abundant in nervous tissue
and heart .
• High levels of ether linked lipids in plasma
membrane of very metastatic cancer cells
have been reported.
• Suggested a role for the lipids in the invasive
properties of these cells.

12. Glycerophospholipids Are Amphipathic

13. Glycerophospholipids Are Amphipathic
• The basic structure of the plasma membrane is the lipid
bilayer.
• Glycerophospholipids contain both a polar and non
polar end.
• Polar head group are in contact with intra or
extracellular aquous phase.
• Whereas non polar tails face each other.

14. Sphingolipids
• The amino alcohols sphingosine and
dihydrosphingosine are the basis for
the sphingolipids.
• Ceramide have a saturated or
unsaturated long chain fatty acyl
group in amide linkage with the amino
group of sphingosine.
• The sphingomyelins, the most
abundant sphingolipids in mammalian
tissues ,have phosphorylcholine
esterified at C1.

15. • Glycosphingolipids contain a sugar linked by a
ẞ-glycosidic bond to C1OH group of a ceramide.
• A subgroup of cerebroside which contain either
glucose or galactose.
• Galactocerebroside predominate in brain and
nervous tissue, whereas glucocerebroside
occur in small quantities of non neuronal
tissues.

16. • The plasma membrane of animal cells contains 4 major
phospholipids, such as –phosphotidylcholine,
phosphotidylserine, phosphotidylethanolamine and
sphingomyelin.
• At neutral pH, the polar head group may have no net charge,
Or it may have net negative charge.

17. Cholesterol
• Cholesterol is the third major lipid in membrane
• Cholesterol is a compact rigid hydrophobic molecule.
• It has a polar hydroxyl group at C3.
• Cholesterol alters the fluidity of membranes .

18. The major lipid components of plasma
membranes:-PC-21%
PE+PS-29%
SM-21%
CHOLESTEROL-26%

19. Glycoproteins or Glycolipids
• Carbohydrates are present in membranes as
oligosaccharides.
• They are covalently attached to the lipids or proteins.
• The carbohydrate is on the extracellular surface of
plasma membrane and the luminal surface of
endoplasmic reticulum.

20. Role of carbohydrates
• Carbohydrates mainly serve as cell to cell recognition
molecules, membrane receptor.

22. LIPID BILAYER

23. Lipid bilayer and Micelles
• The amphipathic compound with a
hydrophilic head and a hydrophobic
tail interact with aqueous systems
in vitro to form a sphere.
• Micelles have only one polar
surface, which is side presented to
the aqueous phase..

24. • The structure of a micelles is very stable .
• Because of hydrophobic interactions between
hydrocarbon chains and attraction of polar head
group to water.
• Micelles are important in intestinal digestion and
absorption of lipids

25. Mobility of lipid components in membrane
• Lipid bilayer not rigid and static structure.
• Lipid molecules can rotate freely around
their long axis and diffuse laterally within
each leaflets.
• All phospholipids of plasma membrane
are mobile, they are not fixed.
• They are moving laterally
.
• The transition of a lipid molecule from
one leaflet to the other is called
transverse diffusion.

27. FLUID MOSAIC MODEL
 In 1972 SJ Singer and GL Nicolson proposed fluid
mosaic model.

28. Asymmetry Of Lipid Bilayer
Outer leaflets
• Lots of carbohydrates.
• Sphingomyelin and
phosphotidylcholine.
• Cho moities are present.
• Floppase is an outward-
directed ATP-dependent
transporter.
Inner leaflets
• Carbohydrates does not have
significant role.
• Phosphotidylserine and
phosphotidylethanolamine.
• Absent
• Flippase is an inward-directed
ATP-dependent lipid class of
transporters.

30. Membrane Protein
Integral protein Peripheral protein
• Integral proteins are permanently
attached to the membrane.
• Embedded in the whole membrane.
• Serve as carrier proteins, channels,
&enzymes.
• Detergents should be used to
remove integral proteins.
• Glycophorin are the example of
integral proteins.
• Peripheral proteins are temporarily
attached to the membrane.
• Located on the inner or outer surface of
the phospholipid bilayer.
• Serve as receptors and surface antigens.
• Peripheral proteins removed by salt, pH
changes
• Erythrocyte spectrin are the example of
peripheral proteins.

31. Integral proteins
 Integral membrane proteins are embedded are asymmetric in the membrane
 Integral proteins are mostly transmembrane proteins.
 All transmembrane proteins are amphipathic
 Protein that are held in lipid bilayer very tightly .

32. Types Of Integral Proteins Structure
• 6 different types of ɑ-helix protein structure
primarily of hydrophobic amino acids.
TYPE-1
TYPE-2
C
N
N
C

33. TYPE-3 Multiple trends in single polypeptide.
TYPE-4
Consists of several different
polypeptides assemble together in a
channels through the membrane.
TYPE-5
Proteins are anchored to lipid bilayer
through covalently linked lipids.
Type-6 Proteins have both transmembrane
domains & lipid anchors.

34. Have specific protein which serve as channels
carrier protein, enzymes and receptors.
A+B C+D

35. Fluidity of a lipid bilayer
• Although the lipid bilayer structure is quite stable
its individual phospholipid & sterol molecules have much
freedom of motion which is main reason of fluidity property of
lipid bilayer.
• Membrane fluidity is influenced by:
-Temperature
-Fatty acid composition
-sterol content

36. Fluidity Of Lipid Bilayer
Low temperature
• Fluid like organization
• Polar head loosely packed
• Tailed disordered
• Membrane thinner
• Fatty acid unsaturated
High temperature
Phase transition
• Fluid like organization.
• Polar head loosely packed
• Tails disordered.
• Membrane thinner.
• Gel like organization.
• Polar head tightly packed.
• Tails regular
• Membrane thicker

38. Abnormalities of Cell Membrane Fluidity in Disease
• A major factor in the fluidity of the membrane in higher organisms
and mammals in the presence of cholesterol.
• In case of spur cell anaemia, erythrocyte membrane of individuals
have increased cholesterol content & a spiny shaped.
• Cells are destroyed prematurely in the spleen.
• This condition occurs in severe liver disease such as alcoholic
cirrhosis.
• Increase intracellular membrane cholesterol which affect their
fluidity.
• The intoxicating effect of ethanol on the nervous system is probably
due to modification of membrane fluidity, altering membrane
receptors and ions channels.

39. Lipid Rafts
• Lipid rafts are membrane microdomains enriched in
sphingolipids,cholesterol and certain lipid-linkedproteins.

40. • Rafts is mainly responsible for signaling and
communication.
LIPID RAFTS
Caveolin
Non caveolar

41. Caveolins
• Caveolin (caveolae”little caves’)
• Integral membrane protein.
• Two globular domains connected
by hairpin like hydrophobic structures.
• Bound inward to cytoplasmic
leaflet.
FUNCTIONS-
- Membrane trafficking
- Signal transduction

42. Dynamic Nature of Membrane
Diagram indicate the relationship of for membrane-
associated proteins with the lipid bilayer.

43. • Some membrane protein movement is restricted.
• Cellular membrane are in a constantly changing
state, with movement of proteins and lipids laterally,
changes in association of lipid anchored proteins and
molecules into and out of the membrane.

44. “THANK YOU”