1. Cell membrane composition Lecture NO:1, 1st MBBS
Dr Muhammad Ramzan

2. Cell membrane – the definition
Is a biological membrane that separates the interior of all cells from the outside environment
Also called as plasma membrane
Protects and maintains the integrity of a cell
- on line.org

3. Cell membrane – the background
Is selectively permeable to ions and organic molecules
Controls the movement of substances in and out of the cells.
Source of Communication B/W with the cells
Fundamental structure consists of Phospholipids Bilayer with embedded proteins
It is thin, Pliable and 7-10nms thick and envelops the cell
britannica.com

4. Plasma membrane – electron micrograph Rail road track
The plasma membrane is referred to as rail road track that appears as Dense lines on :
Electron micrographs that run parallel and are separated by an intertwining space
(space between the 2 lines appears divided)

5. Cell membrane - Rail road track

6. Cell membrane composition Proteins, Lipids and CHOs
Cell membrane consists of:
Proteins (55%)
Phospholipids (25%),
Cholesterol (13%)
Other lipids (4%)
And Carbohydrates (3%).

7. Membrane proteins – the major component
Proteins are the major component of the plasma membrane and consist of 50-55% by weight
Proteins are much larger molecules than lipids
1/one mole of protein = moles of lipids

8. Synthesis of Membranous proteins The Ribosome
Membranous proteins are synthesized in the RER of all the cells
Are transported to the Golgi and further to the plasma membrane for their maintenance
CHOs groups are added to the polypeptide chains both in RER and Golgi apparatus
Most of the Trans membrane proteins are Glycoproteins with their oligosaccharides exposed on their cellular surface

9. Membrane proteins – Types Two (2)
Major membranous proteins are of 2 types based on the
Nature of the membrane and protein interactions
Integral/ Tran membrane/intrinsic proteins
Peripheral membrane/Extrinsic proteins

10. Integral /Trans membrane proteins Exposed to aqueous environment on both sides
These proteins cross the entire thickness of the membrane and are its structural/functional component
Are firmly attached to membrane and lipid Bilayer
Cannot be removed without disrupting the cell
Are mostly Glycoproteins to span the lipid Bilayer 3
Include: Ion channels; Transport proteins, GPCR, LDL –receptors and enzymes
- on line.org

11. Trans membrane/Integral Proteins

12. Trans membrane Proteins - GPCR

13. Peripheral proteins - Characteristics Do not pass through the lipid Bilayer
Are Indirectly associated with the membrane through protein - protein interactions or Ionic bonds or
Directly to the surface of integral proteins, either on the Cytoplasmic or extracellular side
They do not cross through the lipid Bilayer
They can be removed from the membrane through polar agents without disrupting phospholipids Bilayer

14. Integral and Peripheral proteins

15. Peripheral proteins – the role
Some of the peripheral proteins are water soluble enzymes that act on the water soluble heads of the :
membranous Phospholipids
These Phospholipases hydrolyze various bonds in the heads of phospholipids and :
Degrade the damaged or aged cell membranes

16. RBC membrane composition – A model special characteristics
Plasma membrane of the Human Erythrocyte is a model for membrane studies as it has :
No nuclei and internal membranes
Can easily be isolated for biochemical analysis
Studies of the RBC plasma membrane provided the first evidence of the existence of Phospho lipid Bilayer 3

17. Tran membrane proteins of RBC the types
Major Trans membrane proteins are :
Glycoproteins,
Glycophorins and Band 3
Aquaporin
RH(Rhesus) proteins
The red cell glucose transporters (GLUT-1)

18. Tran membrane proteins of RBC
Glycophorins are proteins that contribute to the Glycosylation
Aquaporins is a water channel protein in renal tubules
RH (Rhesus) protein is one of the most immunogenic human blood group system
The Red cell Glucose transporter(GLUT1) is passive one and is present in other tissues also.
Band 3 is an anion transporter for HCO3 and Cl͞

19. Trans membrane Proteins of RBC

20. Integral protein of RBC- Role of Band 3 anion transporters

21. Membranous lipids – 3 types
The cell membrane consists of 3 classes of amphepathic lipids:
Phospholipids, Glycolipids and Cholesterol
The amount of each depends upon the type of cell
In majority of the cases phospholipids are the most abundant
In RBC studies 30% of the plasma membrane is lipid

22. Membranous lipids

23. Cell membrane – Fluid mosaic model pieces of elements are fitted togother
It describes the structure of plasma membrane as a mosaic of its components which:
Includes Proteins; phospholipids, Cholesterol and CHO
It gives fluid character to the cell membrane in which proteins move freely and laterally in lipid Bilayer
Fluidity is due to the Unsaturated FAs that are unable to pack

24. Lipid Bilayer and its composition Lipids and proteins
It is primarily a thin layer of Phospholipids, both on the Cytoplasmic and extracellular surfaces :
Resulting in Bilayer with embedded proteins
The head is Hydrophilic with Phospholipids and tail is
Hydrophobic having CH and FAs in the middle
It is maintained by the : 1. hydrophobic, non covalent
interactions and H2 bonds

25. Phospholipids Bilayer

26. Lipid Bilayer and Membrane fluidity the basis
The FAs are usually unsaturated; have kinks, unable to pack and move freely within the membrane as Fluid 1
The membrane is soft and flexible as a result
It allows the movements of the moles especially of proteins laterally, and prevents vertical movements 3
Lipid Bilayer go through self assembly process for membrane formation in SER

27. lipid Bilayer – the significance
Lipid Bilayer is critical for membrane function:
It isolates the 2 aqueous compartments : Cytoplasmic and extra cellular from each
Ensures membrane Semi permeability
Maintains Fluidity of the cell membrane
Embedded proteins give Fluid Mosaic appearance to the membrane 4

28. Membranous Carbohydrates (CHO)
Carbohydrates form a layer on the extracellular surface of the cell membrane – Glycocalyx
It protects the cell from physical and chemical injuries and act as adhesions B/W the cells
Prevents the invasion of pathological agents like Bacteria and Virus

29. Significance of carbohydrates
Carbohydrates are attached to the Lipids as Glycolipids on the outer cell surface as :
blood group antigens – important in blood transfusions
Glycoproteins are Proteins with CHOs
These serve as cell surface receptors GPCR and hormones like . All ant. Pituitary hormones)