INTRODUCTION plasma membrane is also known as cell membrane or cytoplasm membrane. It is the biological membrane, separates interior of the cell from the outside environment. Selective permeable to Ions and organic molecules. Its basic function is to protect the cell from its surroundings. It consists of the phospholipids bilayer with embedded proteins. Cell membranes are involved in:cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for several extracellular structures.

1. PREPARED BY:
BASHARAT NAUMAN
REG# 5537
MICROBIOLOGY 3RD STR
ABASYN UNIVERSITY
PESHAWAR

2. CHEMICAL COMPOSITION OF
PLASMA MEMBRANE
•Introduction
•Chemical composition
•Molecular structure
•Membrane lipids
•Membrane proteins
•Membrane carbohydrates
•Structural organization of cell membrane

3. INTRODUCTION
 plasma membrane is also known as cell
membrane or cytoplasm membrane.
 It is the biological membrane, separates interior
of the cell from the outside environment.
 Selective permeable to Ions and organic
molecules.
 Its basic function is to protect the cell from its
surroundings.
 It consists of the phospholipids bilayer with
embedded proteins.
 Cell membranes are involved in:
cell adhesion, ion conductivity and cell
signaling and serve as the attachment surface for
several extracellular structures.

4. Chemical composition:
 Cell membranes contain a variety of biological
molecules, notably lipids and proteins.
 Some of the proteins and lipids, however, may
have oligosaccharides, covalently attached to
them.
 The sugar containing sequences of these
glycoprotein and glycolipids also play a role in
determining the identity of cells.

5. Molecular structure:
The molecular structure of cell membrane id
totally dependent on:
(a) Membrane Lipids
(b) Membrane Proteins
(c) Membrane Carbohydrate

6. a) Membrane lipids
 The cell membrane consists of three classes
of amphipathic lipids: phospholipids, glycolipids,
and sterols.
 The fatty chains in phospholipids and glycolipids
usually contain an even number of carbon atoms,
typically between 16 and 20.
 The entire membrane is held together via non-
covalent interaction of hydrophobic tails.
 In animal cells cholesterol is normally found in the
irregular spaces between the hydrophobic tails of the
membrane lipids, where it confers a stiffening and
strengthening effect on the membrane.
 The major lipids in the cell membrane is
phospholipids.

7. Phospholipids molecule

8. Continued….
 Each phospholipid molecule has hydrophilic
(polar) head and a hydrophobic (non-polar) tail.
 The hydrophilic heads interact with water while
hydrophobic tails remain away from it and in
contact with each other.
 hydrophilic and hydrophobic molecules interact
differently with water.
 hydrophilic molecules dissolve readily in water
because they contain charged groups or
uncharged polar groups that can form either
favorable electrostatic interactions or hydrogen
bonds with water molecules.
 Hydrophobic molecules, by contrast, are insoluble
in water because almost all, of their atoms are
uncharged and nonpolar and therefore cannot

9. Continue…
 For that reason, lipid molecules spontaneously
aggregate to bury their hydrophobic tails in the
interior and expose their hydrophilic heads to
water.
 The lipid molecules exchange positions
horizontally (laterally) with their neighbours in the
same layer.
 In this energetically most-favorable arrangement,
the hydrophilic heads face the water at each
surface of the bilayer, and the hydrophobic tails
are shielded from the water in the interior.

10. Membrane Proteins
 The cell membrane has large content of proteins,
typically around 50% of membrane volume.
 large variety of protein receptors and
identification proteins, such as antigens, are
present on the surface of the membrane.
 Functions of membrane proteins can also include
cell–cell contact, surface recognition,
cytoskeleton contact, signaling, enzymatic
activity, or transporting substances across the
membrane.

11. Continue…
 There are three types of proteins in plasma
membrane.
 Integral proteins, Transmembrane proteins and
Peripheral proteins.

12.  Integral proteins are usually globular and they
normally extend in the interior of the lipid bilayer.
 It directly interacts with hydrophobic regions of
the bilayer.
 The hydrophilic regions of integral proteins are
generally exposed to the cytoplasm and external
aqueous phase outside the cell.
 They carry out all the functions of the membrane
such as transport of molecules across the
membrane, receiving signals from hormones and
establishing cell shape.
Transmembrane proteins are also integral
proteins.

13.  Transmembrane protein is a type of integral
protein spanning the entirety of the biological
membrane to which it is permanently attached.
 transmembrane proteins span from one side of a
membrane through to the other side of the
membrane.
 Many transmembrane proteins function as
gateways to deny or permit the transport of
specific substances across the biological
membrane, to get in or out of the cell as in the
case of waste byproducts.

14.  Peripheral membrane proteins are proteins that
adhere only temporarily to the biological
membrane with which they are associated.
 These molecules attach to integral membrane
proteins, or penetrate the peripheral regions of
the lipid bilayer.
 The reversible attachment of proteins to biological
membranes has shown to regulate cell signaling and
many other important cellular events.
 Membrane binding may promote rearrangement,
dissociation, or conformational changes within many
protein structural domains, resulting in an activation of
their biological activity.

15. Membrane Carbohydrate
 Carbohydrates (oligosccharides) in plasma
membrane occur as glycol proteins and
glycolipids most of the membrane carbohydrates
are bound to protein molecules.
 Carbohydrate chains of all the cell membranes
are located extensively on the exoplasmic
surface, i.e. outside the cell.
 Although the functions of membrane
carbohydrates are yet to be established, they
seem to be involved in cell communication and
recognition processes.

16. Structural organisation of
plasma membrane:
 the mid 19th century, Moritz Traube noted that the
outer layer of cell is semi permeable to allow transport
of ions. Traube had no direct evidence for the
composition of this film, though, and incorrectly
asserted that it was formed by an interfacial reaction
of the cell protoplasm with the extracellular fluid.
 The fatty and oily nature of the cell membrane was
first correctly intuited by Quincke, who noted that a
cell generally forms a spherical shape in water and,
when broken in half, forms two smaller spheres.
 In 1902 Hans Meyer and Ernest Overton proposed
that the plasma membrane is composed of a thin
layer lipid molecule.
 James Danielli and Hugh Davson in 1935 proposed
the lipid bilayer model.

17. Continue…
 In early 1960, David Robertson proposed that,
plasma membrane was of uniform thick with two
protein (outer and inner) coats and middle
phospholipid bi-layer.
 John Singer and Garth Nicolson modified David’s
model and called it fluid mosaic.

18. FLUID MOSAIC MODEL

19. Continued…
 John Singer and Garth Nicolson proposed the fluid
mosic model of the plasma membrane.
 According to this model biological membranes can be
considered as a two-dimensional liquid in which lipid
and protein molecules diffuse more or less easily.
 Although the lipid bilayers that form the basis of the
membranes do indeed form two-dimensional liquids
by themselves, the plasma membrane also contains a
large quantity of proteins, which provide more
structure.
 Examples of such structures are protein-protein
complexes, pickets and fences formed by the actin-
based cytoskeleton, and potentially lipid rafts.

20. references
 www.wikipedia.org/introduction,chemical...
 www.mville.digication.com
 www.profosinubi.com