BIOE 1010 Week 6
BIOE 1010 Week 6 BIOE 1010
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This 3 page Class Notes was uploaded by Sara Littlejohn on Wednesday February 10, 2016. The Class Notes belongs to BIOE 1010 at Clemson University taught by Dr. Vladimir Reukov in Spring 2016. Since its upload, it has received 16 views. For similar materials see Biology for BioEngineers in Bioengineering at Clemson University.
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Date Created: 02/10/16
Module 4 Cell Membranes Bold red text=this material will be on Exam 2 Lipids: Structure and Function of Plasma Membranes Lipids: chemically diverse group of compounds o Common feature: insolubility in water (soluble only in organic compounds) Fatty acids have two regions. o Amphipathic molecules: possess both hydrophilic and hydrophobic regions o Can be saturated or unsaturated Saturated: has hydrocarbon chains connected by single bonds only Unsaturated: has one or more double bonds Each double bond may be in a cis or trans configuration o Cis: both hydrogens are on the same side of the hydrocarbon chain (Causes a kink in the chain) o Trans: hydrogens are on opposite sides Triacylglycerol (Triglycerides): formed by the joining of three fatty acids to a glycerol backbone Phospholipid: molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone o Introducing a phosphate group makes phospholipid head very hydrophilic o The phosphate may be modified by the addition of charged or polar chemical groups o Two chemical groups that may modify the phosphate are choline and serine o Both choline and serine attach to the phosphate group at the position labeled R o They spontaneously aggregate and form bilayer membranes in water. Cholesterol o Cholesterol fits into the gap between two phospholipid molecules in an lipid bilayer and modulates its fluidity o Factors that affect fluidity of the membrane: Temperature Cholesterol o Because it’s a short and rigid molecule, cholesterol tends to stiffen the membrane making it more rigid and less permeable Fluid Mosaic Model o The lipid bilayer gives the membrane its basic structure and serve as a permeability barrier Cell Membranes: separate and protect chemical composition Internal Membranes: enclose intracellular compartments to form organelles Plasma Membranes and internal membranes are barriers: they prevent molecules on one side from mixing with those one the other side. Membrane Proteins: carry out most membrane functions o Transport nutrients o Anchor the cell o Receptors o Enzymes catalyze specific reactions Transmembrane Protein: hydrophobic regions lie in the interior of the bilayer, near the hydrophobic tails of the lipids o Hydrophilic regions are exposed to the aqueous environment on either side of the membrane The plasma membrane is a barrier BUT cells need to exchange molecules with their environment: Import nutrients, Eliminate waste, regulate the intracellular concentrations of inorganic ions. ONLY Small uncharged molecules diffuse across the membrane. o The smaller and more hydrophobic, the more rapid the diffusion through the lipid bilayer. Simple Diffusion: Diffusion through a permeable membrane moves a substance from an area of high concentration down its concentration gradient (into cytoplasm). Transport Classification 1: o Transporters (Carriers): solute molecules fit into specific binding sites; when proteins change conformation, the solute is releases on the other side of the membrane. o Channels (Provide Corridors): discriminate ions based on size and electric charge; channels can be opened or closed by the cell, as needed. Much faster than transporters Transport Classification 2: o Single Uniporter: carries one molecule or ion. o Coupled Symporter: carries two different molecules or ions, both in the same direction Antiporter: carries two different molecules or ions, but in different directions Transport Classification 3: o Passive: transport occurs down the concentration gradient aided by proteins; gives energy o Active: transport occurs against the concentration gradient; needs energy Electrochemical Gradients: when voltage and concentration gradients exist o Primary active transport moves ions across a membrane, creating an electrochemical gradient.
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