1. By/ Dr. Magda Ibrahim Lecturer of Medical Biochemisrty
Biological membranes
By/
Dr. Magda Ibrahim
Lecturer of Medical Biochemisrty

2. Describe the composition and architecture of biological membrane.
By the end of this chapter, you should be able to :
Describe the composition and architecture of biological membrane.
Summarize the fluid mosaic model of membrane structure.
Explain the inside-outside and regional membrane asymmetry
identify the factors which cause and maintain membrane fluidity
Identify the diseases related to the membrane

3. Chemical composition Lipid, protein, CHO Diseases related to membrane
Biological membranes
Characteristics
Chemical composition Lipid, protein, CHO
Asymmetry
inside-outside
Regional
Fluid- mosaic model
Diseases related to membrane

4. Characteristics of cell membrane
1- Flexible
(permits the shape changes during cell growth and division
2- Enclosed specialized compartments inside the cell ( i.e mitochondria, nucleus)
3- Selective permeability and acts as a barrier
to maintain differences in composition between inside and outside.
4- self sealing
(ability to break and reseal two membranes as in cell division.
5- Exchange materials with extra cellular environment (exocytosis and endocytosis) and with adjacent cell through gap junction
6- It plays an important role in :
Cell-cell interaction
Trans-membrane signaling
7-It localize enzymes, it provides energy production as in oxidative phosphorylation.
8-Thermodynamically stable, and metabolically active
9-Changes in membrane structure can affect water balance and ion influx , and may lead to variety of diseases

5. Plasma membrane (Cell membrane)
Separates inside from outside
Intracellular fluid (ICF)
Inside cells (cellular protoplasm)
Extracellular fluid (ECF)
Outside cells
ECF
ICF

6. Characteristics of cell membrane
1- flexible (permits the shape changes during cell growth and division.
2- Enclosed specialized compartment inside the cell ( i.e mitochondria, nucleus)

7. 3- selective permeability and acts as a barrier to maintain differences in composition between inside and outside.
4- self sealing (ability to break and reseal two membranes as in cell division.

8. Cell-cell interaction Trans-membrane signaling
5- exchange materials with extra cellular environment (exocytosis and endocytosis) and with adjacent cell through gap junction
6- It plays an important role in :
Cell-cell interaction
Trans-membrane signaling

9. 8-Thermodynamically stable, and metabolically active
7- It localize enzymes, it provide energy production as in oxidative phosphorylation.
8-Thermodynamically stable, and metabolically active
9-Change in membrane structure can affect water balance and ion influx , and may lead to variety of diseases.

10. Cell membrane composition
Lipid
Glycolipid
Glycerophospholipids
Most common is
Phosphatidyl Choline
Sphingophospholipids
- Second major class
Sphingomyelin in myelin sheath
Sterols
Cholesterol is most common
Protein
Carbohydrate

11. Phospholipids bilayer.
The cell membrane is formed of
Phospholipids bilayer.
outside
inside

12. Membrane phospholipids
Fatty acid (tails)
hydrophobic
Phosphate + head group (head)
hydrophilic
Arranged as a bilayer

13. Fatty acids in membrane phospholipids
Membranes are more tightly and less fluid
Membranes are less tightly and more fluid
Straight tails of phospholipid
Kink at the tail of phospholipid
Fatty acids in membrane phospholipids
Saturated fatty acids
Unsaturated fatty acids (cis form)

14. Phospholipid bilayer Outer leaflet Inner leaflet polar hydrophilic
heads
Outer leaflet
nonpolar
hydrophobic
tails
polar
hydrophilic
heads
Inner leaflet

15. Membrane phospholipids A- Types of Glycerophospholipids
Phosphatidyl choline
(lecithin)
Phosphatidyl serine
Phosphatidyl
Ethanolamine
Phosphatidyl inositol

16. B-Sphingomyelin The backbone is sphingosine

17. Sphingomyelin Sphingosine = Serine+ fatty acid (palmitate)
The backbone is sphingosine
Sphingosine = Serine+ fatty acid (palmitate)
Ceramide= Sphingosine+ fatty acid
Sphingomyelin= ceramide + Phosphocholine

18. 2-Cholesterol - What do you know about cholesterol?
The cholesterol content of membranes alters their fluidity. The rigid ring of sterols reduces the freedom of neighboring fatty acid chains to move and so decreases fluidity.

19. 3- Glycolipid Cerebroside= ceramide+ CHO (glucose or galactose)
Ganglioside= ceramide+ chain of oligosaccharide+ one or more sialic acid
Both of them are present in nervous system.
They are responsible to inhibit random cell proliferation and cell adhesion----changes in glycolipids ----cancer

21. Integral proteins Peripheral proteins
- Amphipathic
- Embedded in either sides of membrane
- Firmly associated with hydrophobic interactions to membrane lipids
- So, it can be removed by detergent
Peripheral proteins
In the inner membrane leaflet
They don’t react with membrane phospholipids
Not removed by detergent

22. can be released by salt solution with high ionic con.
Integral proteins
Globular in shape
Peripheral proteins
bound to the hydrophilic region of integral protein and head groups of phospholipid by hydrogen bonds and electrostatic interaction
can be released by salt solution with high ionic con.

23. Integral proteins Peripheral proteins
It spans the membrane ‘trans membrane proteins
They are acting as gate-ways or channels
Peripheral proteins
- Has asymmetrical distribution
They may have enzymatic activity

24. Integral proteins Peripheral proteins
- Amphipathic
- Embedded in either sides of membrane
- Firmly associated with hydrophobic interactions to membrane lipids
- So, it can be removed by detergent
Globular in shape
They are acting as gate-ways or channels
It spans the membrane ‘trans membrane proteins
Peripheral proteins
In the inner membrane leaflet
They don’t react with membrane phospholipids
Not removed by detergent
bound to the hydrophilic region of integral protein and head groups of phospholipid by hydrogen bonds and electrostatic interaction
can be released by salt solution with high ionic con.
- Has asymmetrical distribution
- They may have enzymatic activity

25. Biological Membrane

26. III-Membrane Carbohydrates
It is present in the outer surface in the cell membrane.
It is attached covalenty to :
lipid called glycolipid
Protein called glycoprotein
Types: glucose, galactose, mannose
It may act as antigens in case of ABO blood group.

27. Inside – outside asymmetry
Phospholipids
Choline containing lipids ( Phosphatidyl choline, sphingomyelin) in the outer leaflet
Amino- phospholipids (Phosphatidyl serine& ethanolamine) in the inner leaflet
Cholesterol is present in large quantity in outside more than inside
Proteins
Irregular protein distributions
Carbohydrates
External location of CHO in the form glycolipids and glycoproteins

28. If phosphatidyl serine is present in the outer surface
In platelets during blood clot
Mark the cell for destruction by apoptosis

29. Fluid mosaic model of membrane structure
This model stated that membrane protein like icebergs that float in the sea of phospholipids
The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it

30. Fluid mosaic model of membrane structure
More fluidity
This temp. called “transition temp.” (Tm)
-hydrocarbon chain undergo transition from ordered to disordered state
The fluidity of the cell membrane depend on lipid composition
The hydrocarbon chains are highly aligned to provide a stiff structure
Increase in temp

31. Fluid mosaic model of membrane structure
The longer hydrocarbon chain & saturated FA
Less fluidity
High Tm
Shorter & unsaturated (cis- form) FA
More fluidity
Low Tm

33. Increase in memb. fluidity
Permeability of water and other hydrophilic molecules
Binding of protein to receptor e.g insulin
The lateral mobility of integral protein

34. What are the factors which cause and maintain membrane fluidity?
The fluidity of the cell membrane depends on lipids composition of the membrane
The longer fatty acid -----less fluidity and increase in Tm.
the more saturated fatty acid -----less fluidity and increase in Tm.
Increase in unsaturated fatty acid (cis)
Increase fluidity and decrease in Tm

35. Diseases related to biological membrane
Cystic fibrosis
Mutations in the gene encoding (CFTR) protein-cystic fibrosis transmembrane regulator protein- pulmonary disease with high production of viscous secretions, and pancreatic insufficiency
Familial hypercholesterolemia
Mutations in the gene encoding LDL receptor
Hereditary spherocytosis
Mutations in the gene encoding structural protein in the red cell membrane

36. Transport through cell membranes
I- Transport of small molecules
II- Transport of large molecules
III- Transport of small molecules from one cell to another through intercellular contact

37. I-Transport of small molecules
(1)- simple diffusion
(2)- facilitated diffusion
(3)- Active transport

38. Transport of large molecules
Moving large molecules into & out of cell through vesicles & vacuoles
1-Exocytosis
2-Endocytosis
phagocytosis = “cellular eating”
pinocytosis = “cellular drinking”