BIOPHYSICS By Dr Abdel Aziz M Hussein Lecturer

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

Cell Physiology 3

Biophysics , Abdelaziz Hussein 4

5

6

7

Cell Membrane 8

Cell Membrane 7. 5 nm Z A B F 9

Cell Membrane 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 Ao = Angstrom = 10 -10 of meter) in thickness. Biophysics , Abdelaziz Hussein 10

Cell Membrane Functions 11

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

Functions of Cell Membrane 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

Functions of Cell Membrane 5. Generates transmembrane potentials. ________ ++++++++++++ 14 Biophysics , Abdelaziz Hussein

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

Structure of Cell Membrane 16

17

Components of Cell Membrane • It is formed of 3 components; Lipids 42% Proteins 55% Carbohydrates 3% 18 Biophysics , Abdelaziz Hussein

Cell Membrane Lipids 19

Cell Membrane Lipids 20 Biophysics , Abdelaziz Hussein

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

Cell Membrane phospholipids 22

Cell Membrane phospholipids • Arranged into 2 layers (Lipid bilayer) • Phospholipids molecules resemble the clothes-pin shape • Consist of; 1. Head (PO 4 group) (face the ICF and ECF sides) relatively H 2 O soluble (polar, hydrophilic). 2. Tails (face each other in the interior of the bilayer) → relatively H 2 O insoluble (non-polar, hydrophobic). 23 Biophysics , Abdelaziz Hussein

24

Cell Membrane Proteins 25

Cell Membrane Proteins 26 Biophysics , Abdelaziz Hussein

Types of Cell Membrane proteins 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 27 Biophysics , Abdelaziz Hussein

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

Functions of transmembrane Proteins 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. 29 Biophysics , Abdelaziz Hussein

Functions of integral Proteins on one side • Act as enzymes that activate or inactive metabolic processes. 30 Biophysics , Abdelaziz Hussein

Functions of Peripheral Proteins 31

Functions of Peripheral Proteins 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. Biophysics , Abdelaziz Hussein 32

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

Functions of Glycocalyx • 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 Biophysics , Abdelaziz Hussein 34

35

Intercellular Connections Biophysics , Abdelaziz Hussein 36

Biophysics , Abdelaziz Hussein 37

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

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

Tight Junctions • Functions • They are intercellular pathways for solutes and water. Types They may be; i)Tight (impermeable to solutes and H 2 O) as in the renal distal tubule. ii)Leaky (permeable) as in the renal proximal tubule or gall bladder Biophysics , Abdelaziz Hussein 40

Gap Junctions • 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 Biophysics , Abdelaziz Hussein common pore. 41

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

43

44

45

46

THANKS