Structure of plasma membrane

1.  Biogenesis is the formation (production) of new living
organisms or organelles.
 According to Louis Pasteur living things come only from
other living things, by means of reproduction.
 That is, life does not arise spontaneously from non-living
material.
Biogenesis:

2. Structure of Plasma membrane :
By
Dr. Harinatha Reddy A
Department of Biotechnology
Christ University
Unit VII Plasma Membrane and its Functions

3. Introduction:
 All cells and many subcellular organelles are bounded by thin
membranes of phospholipid bilayer.
 The cell membrane is primarily made up of four things:
1. Phospholipids 2. Cholesterol 3. Proteins 4. Carbohydrates
Composition of membranes:
(45% lipid and cholesterol ~50% protein ~5% carbohydrate (linked to
lipids and proteins)

4.  Red blood cells

5.  Mammalian red blood cells do not contain nuclei or internal
membranes.
 so they represent a source from which pure plasma membranes
can be easily isolated for biochemical analysis.

6.  The cell membrane (also known as the plasma membrane or
cytoplasmic membrane) is a biological membrane that separates
the interior of all cells from the outside environment.
 It consists of a lipid bilayer with embedded proteins.

7. Phospholipids:

8. Phospholipids:
 There are two important parts of a phospholipid: the head and the
two tails.
 The head is a phosphate molecule that is attracted to water
(hydrophilic).
 The two tails are made up of fatty acids (chains of carbon atoms)
that repel, water (hydrophobic).

9.  The plasma membranes of animal cells contain four major
phospholipids:
1. Phosphatidylcholine,
2. Sphingomyelin.
3. Phosphatidylethanolamine,
4. Phosphatidylserine,
5. Phosphatidylinositol minor phospholipid.
Phospholipids types:

10.  These phospholipids are asymmetrically distributed between the
two membrane bilayer.
 The outer leaflet of the plasma membrane consists mainly of
phosphatidylcholine and sphingomyelin.
 whereas phosphatidylethanolamine and phosphatidylserine are
the predominant phos-pholipids of the inner leaflet.

11.  A fifth phospholipid, phosphatidylinositol, is also localized to
the inner half of the plasma membrane.
 Although phosphatidylinositol is a quantitatively minor
membrane component, it plays an important role in cell
signaling.

12.  Cholesterol: on the other hand, is a major membrane
constituent of animal cells.
 It present in about the same molar amounts as the phospholipids.
 Cholesterol molecules,
Scattered in the lipid bilayer .
 Without cholesterol, cell
membranes would be too
fluid..

13. Carbohydrates:

14. Carbohydrates:
 Carbohydrates are bound to the membrane in the form of
glycoproteins and glycolipids.
 The glycolipids, glycoproteins are found exclusively in the outer
leaflet of the plasma membrane, with their carbohydrate portions
exposed on the cell surface.

15. Membrane Proteins:
 While lipids are the fundamental structural elements of membranes.
 Proteins are responsible for carrying out specific membrane
functions.

16.  In 1972 Jonathan Singer and Garth Nicolson proposed the fluid
mosaic model of membrane structure.
 According to this theory membrane proteins float like icebergs in lipid
bilayer sea..
FLUID MOSAIC MODEL

17.  Singer and Nicolson distinguished membrane-associated proteins in
to two types called …
1. Peripheral
2. Integral membrane proteins.
Peripheral
Peripheral

18. Peripheral membrane proteins:
 Adhere only temporarily to the biological membrane.
 These proteins attach to integral membrane proteins, or
penetrate the peripheral regions of the lipid bilayer.
 Peripheral membrane proteins easily dissociates from the membrane
following treatments with high salt concentration solutions that do
not disrupt the phospholipid bilayer.

19. Integral membrane proteins:
 An integral membrane protein that is permanently attached and
inserted in to the biological membrane.
 So they can be dissociated only by reagents that disrupt hydrophobic
interactions.
 The most commonly used reagents for solubilisation of integral
membrane proteins are detergents

20.  Many integral proteins are transmembrane proteins, which
extent width and length of the lipid bilayer with portions exposed
on both sides of the membrane.
• Many trans-membrane proteins function as gateways to permit the
transport of specific substances across the biological membrane.

21.  Bacterial plasma membranes usually have a higher proportion of
protein than do euKaryotic membranes.
 Most membrane-associated lipids are structurally asymmetric
with polar and nonpolar ends and are called amphipathic.

22.  Peripheral proteins are loosely connected to the membrane and
can be easily removed.
 They are soluble in aqueous solutions and make up about 20 to
30% of total membrane protein.
 About 70 to 80% of membrane proteins are integral proteins.
These are not easily extracted from membranes and are
insoluble in water.

23. Functions of plasma membrane:
 The basic function of the cell membrane is to protect the cell from
its surroundings.
 The cell membrane controls the movement of substances in and
out of cells and organelles.
 In this way, it is selectively permeable to ions and organic
molecules.

24. Functions of plasma Membrane:
Thus the membrane prevents the loss of essential components
through leakage.

25. Functions of plasma Membrane:
Transport systems can be used for such tasks as nutrient
uptake, waste excretion, and protein secretion.
 The procaryotic plasma membrane also is the location of a
variety of crucial metabolic processes: respiration,
photosynthesis, the synthesis of lipids.

26. THANK YOU……………
by A.H.REDDY