University:
Glendale Community College
Course:
CHM152 | General Chemistry II
Academic year:

2021
Views:

220

Pages:

12
Author:

boltakvf

Section 11.2: Membranes §Membrane - noncovalent heteropolymer of lipid bilayer and associated proteins §Membrane Structure §Proportions of lipid, protein, and carbohydrate vary considerably among cell types and organelles Section 11.2: Membranes Figure 11.25 Lateral Diffusion in Biological Membranes Fluid Mosaic Model – accepted description of biological membranes §Phospholipids – structural component; active agents on surface §Largely responsible for many membrane properties §Fluidity – lateral motion of components in membrane §Proteins ‘float’ & move in it’s plane §Mosaic – 2 components exist side by side §No covalent bonds between proteins & lipids Section 11.2: Membranes §Flipase - movement of phospholipids from one side of a membrane to other §Fluidity - depends on unsaturated fatty acids and cholesterol §Higher unsaturated fat greater fluidity §Cholesterol contributes to stability with its rigid ring system; fluidity with its flexible hydrocarbon tail Figure 11.24 Diagrammatic View of a Lipid Bilayer Section 11.2: Membranes Figure 11.26 Integral and Peripheral Membrane Proteins §Membrane Proteins—facilitate movement of molecules across membrane; peripheral or integral §Peripheral – loosely bond to outer membrane §Integral – embedded in or pass through membrane Section 11.2: Membranes Figure 11.30 Transport across Membranes §Membrane Function §Membrane transport – getting things in and out §Catalysis – reactions on membrane §Receptor – signals biochemical responses Section 11.2: Membranes Figure 11.30 Transport across Membranes §Passive transport - no energy input, down concentration gradient §Simple diffusion - small molecule or ion §Facilitated diffusion – uses carrier or channel protein §Active transport - uses energy to transport molecules against a concentration gradient §Primary – linked to hydrolysis of ATP §Secondary – driven by concentration gradients generated by primary active transport Section 11.2: Membranes Passive diffusion §Simple diffusion - propulsion of each solute by random molecular motion from high concentration to low concentration §Diffusion of gases O2 and CO2 across membranes is proportional to their concentration gradients §Does not require a protein channel §Facilitated diffusion - channel proteins to move large or charged molecules down their concentration gradient §Examples include chemically gated Na+ channel and voltage-gated K+ channel Section 11.2: Membranes §Primary active transport – Na+/K+ ion pump §Sodium ions out, potassium ions in §Na+-K+ ATPase – provides energy §Assumes 2 conformations – E1 and E2 Section 11.2: Membranes Figure 11.31 The Na+-K+ ATPase and Glucose Transport §Secondary active transport - concentration gradients formed by primary active transport are used to move other substances across the membrane §Na+-K+ ATPase pump in the kidney drives the movement of D-glucose against its concentration gradient Section 11.2: Membranes Figure 11.33 The Cystic Fibrosis Transmembrane Regulator (CFTR) §Cystic fibrosis - fatal autosomal recessive genetic disorder §cystic fibrosis transmembrane conductance regulator (CFTR) is missing or defective §Retention of Cl- in cells §Missing Phe508 causes folding errors Section 11.2: Membranes §Membrane Receptors - mechanisms by which cells monitor and respond to changes in their environment §Chemical signals bind to membrane receptors in multicellular organisms for intracellular communication §Chemical signal molecules – hormones, neurotransmitters §Other receptors are involved in cell-cell recognition §Lymphocytes bind to cell surface of virus-infected cells §Binding of ligand to membrane receptor causes a conformational change and programmed response §Binding acetyl-choline to acetylcholine receptor opens a cation channel §Involved in embryonic and fetal development Section 11.2: Membranes §Low-density lipoprotein receptor - responsible for uptake of cholesterol-containing lipoproteins into cells §Glycoprotein found on the surface of many cells §Number of receptors increases in response to a need for cholesterol or steroid hormones §Receptor number varies from 15,000 to 70,000, depending on need §Familial hypercholesterolemia - Missing or defective receptor §Often caused by a failure to synthesize the receptor §Results in increased levels of cholesterol in the blood §Leads to heart attacks during childhood or early adolescence