صدق الله العظيم الاسراء اية 58

By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology

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9 A F F B B Z Z Cell Membrane 7.5 nm

Def. It is a very thin elastic semi-permeable membrane (allowing some substances to pass through it and prevent others) that surrounds the cell Thickness: It is about 7.5 nm (75 A o = Angstrom = of meter) in thickness. 10 Biophysics, Abdelaziz Hussein

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1.Separates the cytoplasm from ECF. 2.Maintains cell's internal environment. 12 Biophysics, Abdelaziz Hussein ICF or cytoplasm ECF Cell environment

3. Controls distribution of ions e.g. Na, K in ICF and ECF. 4. Transports of macromolecules into and out of the cell. 13 Biophysics, Abdelaziz Hussein

5. Generates transmembrane potentials. 14 Biophysics, Abdelaziz Hussein _ _ _ _ _ _ _ _

6. Contains receptors for hormones and transmitter substances. 7. Important for signal transduction 15 Biophysics, Abdelaziz Hussein

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It is formed of 3 components; 18 Biophysics, Abdelaziz Hussein Lipids42%Proteins55%Carbohydrates3%

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21 Biophysics, Abdelaziz Hussein  The basic structure of cell membrane  3 types: 1.Phospholipids 2.Cholesterol 3.Glycolipids

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23 Biophysics, Abdelaziz Hussein Arranged into 2 layers (Lipid bilayer) Phospholipids molecules resemble the clothes- pin shape Consist of; 1.Head (PO4 group) (face the ICF and ECF sides) relatively H2O soluble (polar, hydrophilic). 2.Tails (face each other in the interior of the bilayer) → relatively H2O insoluble (non-polar, hydrophobic).

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27 Biophysics, Abdelaziz Hussein 1.Integral or intrinsic proteins → bind to hydrophobic center of the lipid bilayer 2.Peripheral or extrinsic proteins → bind to the hydrophilic polar heads of the lipids or to the integral proteins

28 Biophysics, Abdelaziz Hussein Integral cell membrane proteins are 2 types; a.Transmembrane proteins → span the entire bilayer b.Present on one side

29 Biophysics, Abdelaziz Hussein Act as; a. Channels → for diffusion of small, water–soluble substances. b. Carriers actively transport materials across the bilayer. c. Pumps actively transport ions across the bilayer. d.Receptors : initiate intracellular reactions when activated.

30 Biophysics, Abdelaziz Hussein Act as enzymes that activate or inactive metabolic processes.

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32 Biophysics, Abdelaziz Hussein Peripheral protein may be: i) Peripheral proteins: bind to the intracellular surface of the membrane and contribute to the cytoskeleton. ii) Peripheral proteins: bind to the extracellular surface of the membrane and contribute to the glycocalyx.

33 Biophysics, Abdelaziz Hussein It is composed of glycolipids and glycoproteins and covers the cell membrane. -It is -vely charged

34 Biophysics, Abdelaziz Hussein Functions 1.It binds to the extracellular Ca to stabilize membrane structures. 2.It acts as an attachment matrix for other cells (cell adhesion molecules). 3. Forms antigens of blood groups on RBCs

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38 Biophysics, Abdelaziz Hussein 2 types of intercellular connections A) Tight junctions A) Tight junctions Are attachments between cells at their apical borders B) Gap junctionsB) Gap junctions Are attachments between cells that permit intercellular communications

39 Biophysics, Abdelaziz Hussein At the junction→ the adjacent cell membranes are fused at ridges projecting from adjacent cells 1.Gall bladder. 2.Renal proximal and distal tubules Present in epithelial cells of;

40 Biophysics, Abdelaziz Hussein Functions They are intercellular pathways for solutes and water. Types They may be; i)Tight (impermeable to solutes and H2O) as in the renal distal tubule. ii)Leaky (permeable) as in the renal proximal tubule or gall bladder

41 Biophysics, Abdelaziz Hussein Present in Cardiac ms, smooth ms, and epithelial cells. Not present in neuron or skeletal ms. -They are highly non selective channels allowing all ions and macromolecules to pass. -They consist of 6 similar subunits called connexins on each cell. -Each set (connexon) of subunits is arranged to form a common pore.

42 Biophysics, Abdelaziz Hussein i) In cardiac and smooth ms i) In cardiac and smooth ms → provide a low resistance path for the spread of ionic currents. ii) In other cells ii) In other cells → facilitate the passage of metabolites and intercellular signals between cells.

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THANKS