Overview of Plasma membrane

1. MEMBRANE MODELS

2. What do we mean by the term cell
membrane?

3. FUNCTIONS
• Protects the cell
• Semi permeable barrier
• Maintain the concentration gradients
• Allows cell recognition
• Maintain shape of the cell

4. MODELS OF PLASMA
MEMBRANE
• Gorter and Grendel model.
• Sandwich Model of Plasma Membrane.
• Fluid Mosaic Model of Plasma Membrane.

5. GORTER AND GRENDEL
• Investigated the surface area of lipids.
• They extracted the lipids from RBC of human and
animals in acetone.
• The lipids were spread on a water surface in Langmuir
trough.
• Measured the surface area of the extracted lipid.
• Calculation:
surface area occupied by the extracted lipid
surface area of all RBC membrane.

6. SINCE, THERE IS ENOUGH
LIPID TO GO AROUND
THE RBC TWICE.HENCE,
THEY PROPOSED THE
MEMBRANE AS LIPID
BILAYER.

7. ERRORS
• Acetone does not quantitatively extract all
the lipids
• Their calculation of membrane surface
area also less than actual figure

8. SANDWICH MODEL
•A phospholipid
bilayer is
sandwiched
between two layers
of protein.
•Phospholipid is
essential because
the lipid layer is
permeable to polar
molecules

9. ERRORS
• This model failed to explain the thickness
of the Membrane
• Not all membranes are identical or
symmetrical.
• Membranes with different functions also
differ in chemical composition and
structure.
• Membranes are bifacial with distinct inside
and outside faces.

10. FLUID MOSAIC MODEL

11. Fluid Quality Of Membranes
• It was proposed by Singer and Nicholson.
• Membranes are held together by hydrophobic
interactions.
• Most membrane lipids and some proteins can
drift laterally within the molecules.
• Molecules rarely flip transversely across the
membrane.
• Some membrane proteins are tethered to
cytoskeleton and cannot move far.
• Membrane must be fluid to work.

12. Membranes As Mosaics Of Structure n
Function
• A membrane is a mosaic of different
proteins embedded and dispersed in the
phospholipid bilayer. They vary in both
structure n function. Two types
a. Integral proteins
b. Peripheral proteins

13. INTEGRAL PROTEINS
• Unilateral, reaching only a part way
across the membrane.
• strongly associated with bilayer
• strong, hydrophobic (van de Waals’) forces

14. PERIPHERAL PROTEINS
• Not embedded but attached to
membranes surface.
• On cytoplasmic side, may be held by
filaments of cytoskeleton.

15. CHOLESTEROL : A “FLUIDITY BUFFER
• Cholesterol molecule are embedded in
animal cell membrane not in plant cell
membrane they make the membrane
( along with phospholipids) impermeable to
water soluble substance. it also stables the
membrane.
• Below Tm - cholesterol disrupts close
packing of acyl chains  increases fluidity
• Above Tm - cholesterol constrains motion of
acyl chains  decreases fluidity

16. Membranes are asymmetric.
• The two layers may differ in lipid composition,
proteins in the membrane have a clear
direction.
• The outer surface also has carbohydrates.
• This asymmetrical orientation begins during
synthesis of new membrane in the
endoplasmic
reticulum.

18. CONCLUSION
• It provides a barrier between the inside and
outside environment of the cell, and plays an
important role in cell to cell signaling and
communication.
• It is composed primarily of phospholipids and
proteins, and the exact composition of the
cell membrane varies depending on the cell
type.
• Although there is a wide variety of cell
types which exist in nature, one uniting
feature they share is the cell membrane.