Cell Biology 225 Lecture 11 - Membrane Summary
Cell Biology 225 Lecture 11 - Membrane Summary BIOL 225
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This 3 page Class Notes was uploaded by MelLem on Monday April 4, 2016. The Class Notes belongs to BIOL 225 at Simmons College taught by Dr. Lopilato in Fall 2016. Since its upload, it has received 20 views. For similar materials see Cell Biology in Biology at Simmons College.
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Date Created: 04/04/16
Cell Biology Lecture 11 Summary of Membrane Functions Summary of Membrane functions: • Compartmentalization • Scaffold for biochemical activities • Providing a selectively permeable barrier • Transporting solutes • Responding to external stimuli • Intercellular interaction • Energy transduction Differentiated functions of the plasma membrane of an epithelial cell • Apical plasma membrane o Regulation of nutrient and water intake o Regulated secretion o Protection • Lateral plasma membrane o Cell contact and adhesion o Cell communication • Basal membrane o Cell substratum contact o Generation of ion gradients • Plasma membrane is only 5-‐10 nm wide, extremely thin. Need ~ 5000 membranes to equal the thickness of a page of paper. Membranes • Lipid composition o Prokaryotes lack cholesterol o T cells recognize bacterial by lack of cholesterol • Membrane proteins o Integral o Peripheral o GPI anchored The asymmetry of the membrane lipids inner and outer leaflets • Glycolipids are in the outer leaflet where they act as receptors for ligands. • PE (inner) promotes membrane curvature for membrane budding and fusion. • PS (inner) has a negative charge to bind positively charged lysine and arginine residues on adjacent proteins. • PS (outer) on aging lymphocytes marks the cells for desctruction by macrophages • PI (inner) can be phosphorylated which converts the lipid into phosphoinostitide for signal transduction pathways. (Figure 4.10 The asymmetric distribution of phospholipids (and cholesterol) in the plasma membrane of human erythrocytes. (SM, sphingomyelin; PC, phosphatidylcholine; PS, phosphatidylserine; PE, phosphatidylethanolamine; PI, phosphatidylinositol; Cl, cholesterol.) Types of membrane proteins • Integral membrane proteins • Peripheral membrane proteins • GPI anchored protein (GPI = glycosylphosphatidyl-‐inositol) Studying membrane proteins • Hydropathy Index • Solubilization by detergents o SDS – denaturing o Triton X100 – nonionic and generally nondenaturing • Gel electrophoresis • Location – trypsin digests • Hydropathy index – theres 4 peaks in this diagram, show tha it crosses the membrane 4 times. Ways solutes go across membranes • Passive – does not require energy input o Nonmediated o Transported mediated • Active – requires the addition of energy o Uses ATP o Uses ion gradients Types of Transport • Diffusion – movement of a solute from an area of high concentration to an area of low concentration. • Facilitated diffusion o Carrier proteins undergo conformational changes upon transfer of solute o Channel proteins – no conformational change of protein with transfer of solute • Active transport – requires the addition of energy, typically against the concentration gradient. Diffusion • Simple Diffusion • Osmosis – flow of H2O o Hypotonic – water flows into the cell/ area of higher solute concentration o Hypertonic – water flows out of the cell / area of lower solute concentration o Ex – RBC – hemolysis o Plant cells – plasmolysis and deplasmolysis • Facilitated Diffusion o Solute binds specifically to membrane protein carrier o Michaelis menton Kinetics ▯ Specificity – D glucose not L glucose ▯ Saturation kinetics ▯ Competitive inhibition o Glucose facilitated diffusion GluTa-‐GluT5 • Partition Coefficients – solubility in lipids, measure of hydrophobicity, how non polar a substance is. o More nonpolar means LARGER partition coefficient. Cycstic Fibrosis • Defect in Cl-‐ secretion • Isolation of a gene • CFTR protein • Problem in membrane localization • Gene Therapy • Mutations can occur throughout the CFTR gene causing defects in multiple amino acids of the protein.
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