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Lecture 5

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Department
Biology
Course
Biology 1002B
Professor
Denis Maxwell
Semester
Winter

Description
Lecture 5: Membrane Structure and Transport 1. Fatty acid  Saturated o Tightly linearly packed together (can’t put anymore hydrogens)  Unsaturated o Double bonds introduces bend/kinks o More fluid  Hydrogenation o When hydrogen is added to a carbon-carbon double bond 2. Membrane permeability  Selectively permeable barrier  Fatty acid tails give a hydrophobic area  Glycerol gives a hydrophilic area  Small nonpolar moelcules: O , CO and N 2 2 2 o Diffuses through membrane down a concentration gradient  Small and uncharged polar molecules: water and indole  Small and uncharged molecules are the easiest to get through membrane o Proteins transport glucose and big or charged molecules (ions) 3. Simple diffusion, facilitated diffusion, active transport and ABC transporter  Simple diffusion o Oxygen diffusion driven by free energy change  Facilitated diffusion o Molecule specific channel where potassium and others can leak from high to low concentration  Active transport o One of the many type of ABC transporters in the body o Go against concentration gradient o Endergonic process – requires energy 4. Basic structure of ABC transporter.  Transmembrane domain  ATP binding cassette o ATP binding domain is common to all ABC transport 5. Cystic fibrosis, Cystic Fibrosis Transconductance Regulator (CFTR), ∆F508  Cystic fibrosis o Homozygous recessive o Mucus lining becomes dry and brittle o Problem with gas exchange diffusion o More prone to bacteria and infection  Caused by CTFR mutation o Most common ∆F508 deletion of phenylalanine (delta = deleted, position 508) o Synthesized on ER but gets shuttled to proteosome where protease degrades proteins o Mutated form is still functional but not efficient  Doesn’t get a chance to function due to quality control  Normal o CTFR ABC transport, pumps chloride to epithelial lining o Water will follow to move through by diffusion from epithelial cell to lining  Keeps mucus lining in lungs wet  Prevent build-up of bacteria and dirt o CFTR gets synthesized on ER during secretory pathway that gets protein to plasma membrane 6. Chaperone protein, “ER quality control”  Chaperone protein detects if proteins should be degraded based on proper folding  ER quality control degrades all defected proteins 7. Role of fatty acids in membrane structure.  Phospholipid bilayer o Amphipathic (both hydrophilic and hydrophobic) o Fatty acid tails drives the synthesis of the bilayer  Makes a semipermeable membrane 8. Relationship of fatty acid saturation levels on membrane fluidity.  Organisms can adjust fatty acid composition from saturated  unsaturated  Bacteria, archaea, protists, plants o Increase relative proportion of unsaturated fatty acids in their membrane  Unsaturated fatty acids made during fatty acid biosynthesis o Desaturases removes two hydrogen atoms and introduce double bond o Temperature decreases, desaturase transcript increases  Regulating desaturase transcript regulates amount of unsaturated fatty acids which regulates fluidity  Have different desaturase enzymes o Where specifically unsaturation takes place 9. Relationship of temperature on membrane fluidity.  Low temperature o
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