Membrane Transport Lecture 3 PDF

Membrane Transport Lecture 3 Dr. Amal Ghanim Lecturer of Biochemistry, faculty of Pharmacy, Fayoum University Overview  Phospholipid bilayer is a good barrier around the cell especially for polar hydrophilic molecules  However, for ce...

Membrane Transport Lecture 3 Dr. Amal Ghanim Lecturer of Biochemistry, faculty of Pharmacy, Fayoum University Overview  Phospholipid bilayer is a good barrier around the cell especially for polar hydrophilic molecules  However, for cell survival; some material need to be able to enter and leave the cell  So, Cell membrane (plasma membrane) is selectively permeable (semi permeable).  Certain molecules as glucose, amino acids and lipids can easily enter and exit the cell while excluding other molecules.  Some drugs can also often gain access to the interior of the cell. Factors affecting membrane transport of a substance 1- Concentration gradient of the substance. 2- Size of the substance. 3- Relative solubility of the substance in oil. In general, the smaller the molecule and the more soluble in oil (the more hydrophobic, or nonpolar), the more rapidly it will diffuse across a lipid bilayer. Molecules can be transported across membrane by the following mechanisms: A- transfer of small B- transfer of large molecules molecules 1-Simple diffusion 1-Endocytosis A-Passive B-Facilitated 2-Exocytosis Simple Simple diffusion diffusion 2- Active transport 1-Simple diffusion A- Passive Simple diffusion  Movement of molecules or ions across the membrane from a region of their higher conc. To a region of their lower conc. i.e. the molecules moves down a concentration Gradient  Diffusion stops when equilibrium reached  Passive Simple diffusion need no energy   Rate of transport of hydrophobic molecules depends on solubility of the transported molecules in the hydrophobic core of lipid bilayer  Transmembrane ion channels (protein containing pores) is ex. of Passive diffusion passive transport  Transport several ions like Na, K , Ca ion from their region of high conc. To low conc. B- Facilitated Simple diffusion  Need no energy  Transport of small molecules in the direction of (down)the concentration gradient with the help of specific carrier protein  E.g glucose carrier protein Passive diffusion glucose transporters (GLUTs) Simple diffusion  Differ from passive simple diffusion that when all carrier proteins are saturated transport is stopped Important Note:  Most cells use simple facilitated transport for glucose uptake according To concentration gradient between extracellular fluids and the cytoplasm (A family of glucose transport proteins catalyze facilitated transport of glucose) called glucose transporters (GLUTs)  In other cells, such as intestinal epithelial cells glucose must be transported against concentrated Gradient from intestinal lumen to the intestinal epithelial cells, there an active transport for glucose is necessary. Using another family of transport protein called sodium glucose transport proteins (SGLT) Osmosis  Osmosis is the same thing as diffusion but it refers specifically to water molecules. Osmosis is the passage of water across the membrane from the area of high concentration of water to the area of low concentration of water. Protein channels known as aqua porins enable water to pass through the hydrophobic core of the phospholipids of the membrane.  Osmotic pressure: Difference in solute concentration on opposing sides of the cell membrane generate an osmotic pressure which is often used to express the concentration of the solution. Three important terms related to osmosis Isotonic solution Hypertonic Hypotonic  When the osmotic In comparing two solutions, pressure is the same in the hypertonic solution is the both inside and outside the cell, solution with a greater solute  The external solution concentration relative to the surrounding the cell is said hypotonic solution. to be isotonic (same). Cells maintain their volume in isotonic solutions. Molecules can be transported across membrane by the following mechanisms: A- transfer of small B- transfer of large molecules molecules 1-Simple diffusion 1-Endocytosis Passive Facilitated 2-Exocytosis Simple Simple diffusion diffusion 2- Active transport 2- Active transport Active transport is the pumping of molecules against their concentration gradient  By binding to membrane protein (Ion pumps) Ion pumps transport the molecules or ions with the consumption of ATP (need energy) Energy can gained from sodium - potassium pump ,where hydrolysis of ATP in presence of ATPase enzyme occur to produce energy  The protein act as a pump using ATP to transport the H+ ion against its concentration gradient B- transfer of large molecules 1-Endocytosis The process by which cells take up large molecules The cell internalize extracellular macromolecules to form endocytic vesicle Inside the cell There are 2 types of endocytosis: 1- Phagocytosis 2- Pinocytosis (cell eating) (cell drinking)  Occur only in specialized cells as  It occurs in all cells and lead to macrophages and granulocytes cellular uptake of fluid as they ingest bacteria and fungi  Vesicles of fluid are formed in  They extend pseudopodia the cell membrane without the and surround the bacteria to formation of pseudopods. form phagosomes which fuse with lysosomes forming phagolysosomes inside which the particles are digested 2-Exocytosis  An opposite process to endocytosis  Used to release macromolecules to outside the cell e.g. release of insulin hormones from beta cells of islet of Langerhans in pancreas Facilitated simple When the concentration of diffusion differ than molecules on both sides of a passive simple membrane is the SAME, the diffusion in solution: requirement of A. Carrier Protein A. moves from an area of higher concentration to an area of B. Energy lower concentration. C. Both of them C. has reached an equilibrium D. No difference D. is hypertonic.