The cell membrane is a phospholipid bilayer 7.5-10 nm thick that separates the interior of a cell from its external environment. It is composed of lipids, proteins, and carbohydrates. Lipids make up the majority and form a fluid bilayer with hydrophobic tails facing inward and hydrophilic heads outward. Embedded proteins carry out important functions like transport and cell signaling. The fluid mosaic model describes the cell membrane as a fluid bilayer with integral and peripheral proteins diffusing within. The cell membrane regulates what enters and exits the cell and also serves structural and signaling roles.

1. CELL MEMBRANE

2. OUTLINES
 .What is cell membrane?
 Chemical composition
 Structure of cell membrane
 Function of cell membrane
 Models of cell membrane

3. WHAT IS CELL MEMBRANE ?
 The cell membrane is a biological membrane
separating the inner part of cell from outside
environment.
 It is also called plasma membrane or plasma
lemma .
 It appears in thin section with the electron
microscope as a triple layered structure about 7.5
to 10 nm thick.
 Term coined by C.Nageli and C.Cramer in 1855
and plasma lemma coined by J.Q.PLOWE in 1931.

4. CELL MEMBRANE
 The cell membrane is flexible and allows a
unicellular organism to move.

5. CHEMICAL COMPOSITION
1. LIPIDS : Four classes of lipids are commonly present in
plasma membrane. Phospholipids (most
abundant),spingolipids ,glycolipids and sterols
(e.g. cholesterol). All of them are amphipathic.Cholestrol is
abundant in mammalian cell and is absent in prokaryotic
cells.
2 .PROTEINS :It contains about 50 % proteins. Amount
and type is variable. Myelin cells contain about 23 %
protein internal membrane of chloroplast and and
mitochondria contains 50% protein. Protein of plasma
membrane are of two types ectoproteins and
endoproteins. Plasma membrane contains structural
proteins, transport protein and enzymes. Some of them act
as receptors.

6. CONT…….
 (enzymes present in the cell membrane are Acetyl
phosphatase, acid phosphatase, ATPase, RNAase ,
maltase, lactase, phospholipase etc.)
3 CARBOHYDRATE. : They are present only in the
plasma membrane and present exterior or polar end
of phospholipids at the external surface of plasma
membrane.

7. PHOSPHOLIPIDS
 Phospholipids (PL) has a polar head and non polar
tails.
 The polar head is charged and hydrophobic (loves
water ) facing outward, contains a _PO4 group and
glycerol.
 The non polar tails are hydrophobic (hates water)
facing inward contain 2 fatty acid chain that are non
polar.
 When PL are placed in water it forms spherical
bilayer.

9. MEMBRANE CHOLESTEROL
 The amount of cholesterol
may vary with the type of
Membrane.
 plasma membrane have
nearly one cholesterol per
PL molecule.

10. PROTEINS ARE CRITICAL TO MEMBRANE
FUNCTION

11. STRUCTURE OF CELL MEMBRANE

12. MEMBRANE COMPONENTS

13. FUNCTION OF PLASMA MEMBRANE
 Keeps a cell intact.
 Protective barrier
 Regulate transport in and out of cell (selectively
permeable)
 Small lipids molecules can easily pass , e.g.O2
&CO2.
 Water can freely cross the membrane.

14.  Ions and large molecules cannot pass without
assistance.
 Allow cell recognition.
 Provide anchoring sites for filaments of
cytoskeleton
 Provide a binding site for enzyme.
 Interlocking surface binds cells together (junction)
 Contains the cytoplasm.

15. MEMBRANE STRUCTURE
 Membranes consist of a PL bilayer combined with a
variety of proteins in a fluid mosaic arrangement.
 The surface of cell membrane are hydrophobic
(water loving) and the interior of cell membrane are
hydrophobic (hate water).

16. MODELS OF CELL MEMBRANE
 1 DANIELLI AND DAVSON MODEL
 It is also called sandwich model
 In 1935, Danielli and Davson studied
triglyceride lipids bilayers over a
water surface.
They found that they arranged
themselves with the polar heads
facing outward.
 It always formed droplets (oil in water
) and the surface tension was much
higher than that of cells.

18. ROBERTSON MODEL
 In 1965, Robertson noted the structure of
membranes seen in the electron microscope.
 He saw no spaces for pores in the electron
microscope.
 He hypothesized that the railroad track appearance
came the binding of osmium tetroxide to proteins
and polar groups of lipids.
 proposed unit membrane hypothesis.

20. FLUID MOSAIC MODEL
 According to S . J .Singer and garth Nicolson 1972,
the two biological membranes can be considered
as a two dimensional liquid where all lipids and
proteins molecules diffuse more or less freely.
 Singer studied PL bilayers and found that they can
form a flattened surface on water, with no
requirement for protein coat.
 It occurs in the form of globular protein.
 Widely accepted model.

22. THAT ALL
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