Transport through the Cell Membrane

Transport through the Cell Membrane 1 Abdelaziz Hussein  Organization of Human Body The human body is made up of different systems e.g. digestive system, whose functions are coordinated and integrated together. Each system consists of many organs th...

Transport through the Cell Membrane 1 Abdelaziz Hussein  Organization of Human Body The human body is made up of different systems e.g. digestive system, whose functions are coordinated and integrated together. Each system consists of many organs that made up of many tissues of complementary functions. Each tissue consists of millions of similar cells. The cell is the basic unit of structure and function in the body Each animal cell is surrounded by a cell membrane Abdelaziz Hussein 2 Abdelaziz Hussein 3 Cell (Plasma) Membrane 4 Abdelaziz Hussein  Cell Membrane It is a very thin elastic semi-permeable membrane (allowing some substances to pass through it and prevent others) that surrounds the cell It is about 7.5 nm (75 Ao = Angstrom = 10-10 of meter) in thickness. 5 Abdelaziz Hussein  6 Abdelaziz Hussein  Functions of Cell Membrane 1. It separates the cytoplasm from ECF. 2. It maintains the cell's internal environment. 3. It transports macromolecules into and out of the cell. 4. It controls distribution of ions e.g. Na, K in the ICF and ECF. 5. It generates transmembrane potentials. 6. It contains receptors for hormones and transmitter substances which are important for signal transduction 7 Biophysics , Abdelaziz Hussein  Components of Cell Membrane It is formed of 3 components: 1. Lipids 42%. 2. Proteins 55%. 3. Carbohydrates 3%. 8 Abdelaziz Hussein Cell Membrane Lipids 9 Abdelaziz Hussein Transport through the Cell Membrane 10 Abdelaziz Hussein Transport through the Cell Membrane 11 Abdelaziz Hussein  Transport through the Cell Membrane There are 3 mechanisms for transport of substances through cell membranes; a) Passive transport (Diffusion): It is movement of substances across the cell membrane down its electrochemical gradient. b) Active transport: It is movement of substances across the cell membrane against its electrochemical gradient. c) Vesicular transport: It is the process by which large sized substances are engulfed by the cell membrane to be either pushed inside the cell (endocytosis) or pushed outside the cell (exocytosis) 12 Abdelaziz Hussein  Diffusion It is divided into 3 subtypes: 1.Simple diffusion. 2.Facilitated diffusion. 3.Osmosis (water only) 13 Abdelaziz Hussein  Simple Diffusion It is movement of substances across the cell membrane down its electrochemical gradient by simple movement without the necessity of binding with carrier proteins Mechanisms: It occurs either through; The interstices of the lipid bilayer. The watery proteins channels. 14 Abdelaziz Hussein Simple Diffusion 15  Simple Diffusion Characters: It is characterized by; a) It occurs down an electro- chemical gradient. b) It is passive i.e. no external energy is required. 16 Abdelaziz Hussein  Simple Diffusion Characters: It is characterized by; c) It is not rate-limiting i.e. linear with concentration gradients. d) The diffusion process is not saturable. 17 Abdelaziz Hussein  Facilitated Diffusion It is the diffusion of substances across the cell membrane (down electrochemical gradient) which needs the presence of carrier proteins→ carrier mediated diffusion Characters: i) It occurs down an electrochemical gradient ii) It is passive i.e. no energy is required. iii) It requires the presence of a transport carrier protein. iv) It is rate-limiting and saturable because it depends on the availability of a definite number of carrier or channel proteins 18 Abdelaziz Hussein Osmosis or Diffusion of Water Water diffuses through lipid bilayer of the membrane at high rate like bullets due to: Its small size. Its very high kinetic energy Water moves from high to low concentrations of water 19 Abdelaziz Hussein  II) Active Transport Definition: It is the movement of substances across the cell membranes against an electrochemical gradient. Types: There are 2 subtypes of active transport: i) Primary active transport → obtain its energy directly from the hydrolysis of ATP e.g. Na-K Pump ii) Secondary active transport → use the energy stored in the Na concentration gradient e.g. Na-glucose co-transport 20 Abdelaziz Hussein  II) Active Transport Characters 1. It occurs against the electrochemical gradient 2. It is active i.e. energy is required 3. It requires the presence of a transport carrier protein 4. It exhibits saturation, and competition 21 Abdelaziz Hussein Differences ( ) simple diffusion, facilitated diffusion and active transport Simple diffusion Facilitated Active transport diffusion Electrochemical Downhill Downhill Uphill gradient Energy Doenot need energy Doenot need energy Needs energy Rate Not limited Limited Limited Saturation Not Saturable Saturable Saturable Carrier Do not need carrier Needs carrier Needs carrier 22 Abdelaziz Hussein  III) Vesicular Transport It is the mechanism by which the large sized substances can cross the cell membranes a) Endocytosis The extracellular material is trapped within vesicles that are formed by invagination of the cell membrane It is active process which uses energy 23 Abdelaziz Hussein  III) Vesicular Transport a) Exocytosis The intracellular material is trapped within vesicles, then the vesicles fuse with the cell membrane and release their contents to the ECF It is active process which uses energy e.g. release of hormones, digestive enzymes, 24 Abdelaziz Hussein THANKS