Structure of cell membrane

1. Structural Organisation of
Cell Membrane
By
Jayalakshmi P.S.
Dept of Botany,
Sree Sankara College, Kalady

2. CELL MEMABRANE-outlines the cell, provide definite shape
• Also known as Plasma Membrane
• Both prokaryotic and eukaryotic cells are outlined by cell membrane.
• Cell membrane is dynamic and selectively permeable.
• In 1972, S.J Singer & Garth . L. Nicolson proposed the FLUID
MOSAIC MODEL

3. Structure of Cell membrane
MAIN COMPONENTS:
LIPIDS-54% PROTEINS-46% CARBOHYDRATES-5-10%

4. Structure of a lipid

5. Sterols
Glycerolipids
Cholesterol

6. Triacylglycerols
• also known as triglycerides
• They are the molecules that makeup animal fats and
vegetable oils.
• used as food storage molecules.
• They are made of four components - a glycerol
molecule attached to three fatty acids.
• Eg: palmitic acid, oleic acid, and stearic acid.

7. Glycerophospholipids
• Phospholipids are esters of glycerol
found in the cell membrane.
• The most common phospholipids are
• phosphatidylcholine
• phosphatidylethanolamine
• phosphatidylinositol
• phosphatidylserine
• Phosphatidylglycerol
• Cardiolipin (found in mitochondria)

8. Sphingophospholipids
• Contains sphingosine as backbone (no glycerol)
• Most important- sphingomyelin.
• sphingosine + long chain fatty acid = Ceramide
• phosphoric acid + Choline = Phosphorylcholine
• Ceramide + Phosphoryl group + Nitrogenous base =
Sphingomyelin

9. • Sphingomyelin is one of the principal structural lipids of
membrane in nervous tissue.
• Sphingolipids are present in nerve cells and brain cells.
• Role in cell signalling and apoptosis.

10. Glycosphingolipids
• Sphingolipids with an attached carbohydrate.
• This oligosaccharide content remains on the outside of the cell
membrane where it is important for biological processes such as cell
adhesion or cell-cell interactions.
• Mainly found in CNS

11. • Glycosphingolipids include:
• Cerebrosides
• Gangliosides
• Globosides

12. • Cerebrosides-found in the cell membranes of the neurons
and the muscle cells
• Gangliosides-CNS
• act as distinguishing surface markers that can serve as
specific determinants in cellular recognition and cell-to-
cell communication.
• Globosides
• abundant at nerve endings and at specific hormone
receptor sites on cell surfaces.
• play an important role in molecular recognition

13. Galactolipids
• They are the main part of plant membrane lipids where they substitute
phospholipids
• Chloroplast membranes contain a high quantity of monogalactosyl
diacyl glycerol (MGDG) and digalactosyl diacyl glycerol (DGDG).

14. Cholesterol
• a component of animal cell membrane
• functions to maintain cell integrity and mechanical stability.
• ABSENT in plant cells.
• interacts with the fatty acid
tails of phospholipids to moderate
the properties of the membrane

15. Properties of cell membrane
1. Phospholipid mobility
a. Transition- lateral movement of
phospholipids; very fast
b. Flip-Flop movement- movement of
phospholipids from outer leaflet to
inner leaflet- not energetically
favourable.
c. Rotational movement

16. 2. Lipid asymmetry
Phosphatidyl choline always
present on the extracellular matrix
Phosphatidylserine present
towards cytosol.

17. Inside-PE,PS,PI,PA (PEPSI)
Outside-CO and Sphigomylein

18. 3. Membrane Fluidity
• Depend on the phospholipid
mobility
• The cell membrane fluidity
depends on:
a. saturated vs unsaturated
phospholipids
b. Temperature
• High-fluid
• Low-rigid

19. c. Length of fatty acid tail-
• longer tails more rigid ( hydrophobic
interaction more)
• Short tails-fluid

20. d. Presence of Cholesterol
• Cholesterol modulates membrane
fluidity.
• Cholesterol has more of hydrophobic regions.
• Addition of cholesterol to the unsaturated phospholipid region, makes
the region less fluid and more organised.
• interacts with the fatty acid tails of phospholipids to moderate the
properties of the membrane

21. Membrane proteins
• Membrane proteins are proteins that are part of or
interact with cell membranes
• they are responsible for carrying out majority of the
functions of cell membranes.
• Membrane proteins mediate many processes that are
fundamental for the flourishing of biological cells.

22. Membrane proteins

24. Integral membrane protiens
• An integral, or intrinsic, membrane protein (IMP) is a type
of membrane protein that is permanently attached to
the biological membrane.
• Integral membrane proteins reside within the bilayer membranes
that surround cells and organelles, playing critical roles
in movement of molecules across them and the transduction of
energy and signals.

25. Peripheral membrane proteins
• Peripheral membrane
proteins are membrane proteins that
adhere only temporarily to the biological
membrane with which they are
associated.
• These proteins attach to integral
membrane proteins, or penetrate the
peripheral regions of the lipid bilayer.

26. FUNCTIONS OF MEMBRANE
PROTIENS
1. Selective Transportation
2. Enzymatic functions
3. Cell surface receptors
4. Cell Recognition
5. Intercellular joining/ Cell Adhesion
6. Attachment to Cytoskeleton

27. • Selective Transportation
• Membrane proteins can allow hydrophilic molecules to
pass through the cell membrane
• Transport membrane proteins come in many forms
• some require energy to change shape and actively move
molecules and other substances across the cell membrane.
• They do this by releasing ATP to use as an energy source.

29. • Enzymatic functions
• a membrane protein that is embedded into the
membrane can sometimes be an enzyme, which
may have its active site facing substances
outside of the lipid bilayer.
• These types of enzymatic membrane proteins
can work in teams to carry out the steps in a
particular metabolic pathway
• for eg. breaking down lactose into
carbohydrates and then to
monosaccharides.

30. • Cell surface receptors
• Used for signal transduction
• Some membrane proteins feature a binding site.
• These binding sites are characterized by specific shapes that match
the shape of a chemical messengers like hormones.
• These hormones when bind to the receptors activate many
pathways.

32. • Cell Recognition
• Cell surface identity marker.
• used for identification and recognition between
cells.
• This particular function is useful in the immune
system, as it helps the body recognize foreign cells
that may be causing infection.
• Glycoproteins are one type of membrane protein
that can carry out cell recognition.

34. • Intercellular joining/ Cell Adhesion
• Adjacent cells may have membrane proteins that connect in a range
of different junctions.
• Gap junctions and Tight junctions.
• This function helps cells to communicate with one another, and to
transfer materials between one another.

37. • Attachment to Cytoskeleton
• Cytoskeleton is the system of filaments and fibers in the
cytoplasm of a cell
• Extracellular matrix (ECM) is the network of macromolecules
found outside of cells, such as collagen, enzymes, and
glycoproteins.

38. • Attaching membrane proteins to filaments or fibers in the
cytoplasm are found throughout the cell
• can help the cell to maintain its particular shape.
• It also keeps the location of membrane proteins stable.
• Attaching membrane proteins to the extracellular matrix can help
the ECM to mediate changes that occur in extracellular and
intracellular environments.

44. Carbohydrates in bacterial cell membrane

45. Functions of Cell Membrane
• Integrity of the cell- maintains size and shape
• Controls transport- selectively permeable
• Excludes unwanted materials from entering the cell
• Forms a physical barrier with external environment
• Sensitivity- first part of the cell that is affected by changes in
the extracellular environment

46. • Maintains the ionic concentration of the cell and osmotic
pressure of the cytosol
• Allows electrical and chemical gradient creation
• Forms contact with neighbouring cells –tissue formation