Molecular Biology of the Cell

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Unformatted text preview: Test- 2 TestTwo “short” tests • Membranes (2.5 lectures) - Ch11 Structure Lipids Proteins • Transport (3.5 lectures) – Ch12 Active Facilitative Co-transport Test 2 in about three weeks! STRUCTURE OF CELLULAR MEMBRANES MEMBRANES • Why do we have membranes • What do they do Roles of membranes Compartmentalization Compartmentalization Site of important reactions Site Regulate communication and transport Regulate Cell-cell communication Cell-cell Outline Outline General Properties and Components • Membrane structure Fluid mosaic model • Membrane components Lipids Carbohydrates proteins • Membrane biogenesis Membrane Composition Membrane • Lipid ~ 50% • Protein ~ 50%; ranges from 25%-75% • Carbohydrate – minor component Glycoproteins Glycolipids • Values above for “average” membrane; Values composition of membranes varies composition What makes up a Membrane ? What Lateral Diffusion of Proteins in Membranes Membranes Fig 10-39, MBOC4 Phospholipid Mobility Phospholipid • Lateral diffusion is easier Lateral than vertical- (flip-flop) than • flip-flop requires an flip-flop enzyme Asymmetric Structure of Membrane Membrane Cholesterol Phosphatidylethanolamine Phosphatidylcholine Glycolipid Phosphatidylserine Sphingomyelin Fig 10-14, MBOC4 Self Assembly of Amphipathic Lipids Lipids Cause of bilayer Hydrophilic polar heads face outside, and hydrophobic nonpolar tails face each other Fig 10-4, MBOC4 Membrane Lipids Membrane • Phospholipids • Cholesterol Essential for animal cell membrane function Can be synthesized, not needed in diet Not found in bacterial membranes Membrane lipids Membrane • Fatty acids & lipids • fatty acids fatty saturated saturated unsaturated Phospholipid Structure Phospholipid Phospholipid= Phospholipid= glycerol + 2 FA + Phosphate glycerol Fig 10-2, MBOC4 Sphingolipid Sphingolipid • based on sphingosine (FA + aa based serine) serine) • mainly another FA + phosphate mainly or some other polar group. or • Very long chain hydrocarbon Very long chains form lipid rafts chains Sterols Sterols • 4-multicarbon rings 4-multicarbon from Acetyl-CoA from 15 or 30 C • Cholesterol The primary sterol in animal membranes also found in plants (much lower percentage), also not in prokaryotes other organisms use other sterols for stabilization Cholesterol Function (4) Cholesterol increase mechanical strength of membrane lowers membrane permeability reduces fluidity of membrane at HIGH temp (= reduces more stable) more increases fluidity at LOW temps llowers transition temperature (the owers temperature at which the membrane “freezes” or “melts”) or Membrane fluidity & permeability • Transition temperature is the Temp that the membrane Transition crystalizes ("freezes") or undergoes PHASE TRANSITION TRANSITION e.g. liquid butter to solid butter below transition temp lipids crystalize & below REDUCES diffusion REDUCES membranes NOT fully functional in this state Cells can change the transition temp Cells lower trans. temp (adaption to cold) lower • animals lower trans. temp (adaption to cold) a) increase proportion of Unsaturation (increase the a) number of double bonds) number b) increase cholesterol content • plants a) increase proportion of Unsaturation (increase the a) number of double bonds) number • prokaryotes a) increase proportion of Unsaturation (increase the a) number of double bonds) number b) decrease FA chain length How would an organism adapt to warmer temperatures? Membrane biogenesis. • A. phospholipids originate in ER, A. 1. plasma membrane a. transferred to Golgi via transition vesicles a. b. then exported to plasma membrane via secretory vesicles which fuse with the plasma membrane plasma 2. nuclear membrane is connected to ER 3. mitochondria & chloroplasts much of the lipid is transferred to much mitochondria & chloroplasts via soluble cytoplasmic proteins called lipid transfer proteins or exchange proteins. What makes up a Membrane ? What Thought Question Thought • Properties of a Membrane are determined by the structure of the lipid Properties molecules. Predict what would happen to the lipid bilayer if the following were true (or happened) were 1. Phospholipids (PL) have had only one hydrocarbon (HC) chain instead of two 2. HC chains were shorter (10 carbons) 3. All HC were saturated 4. All HC were unsaturated 5. Bilayer contained a mixture of two kinds of lipid molecule: One with two saturated 5. HC tails and one with two unsaturated HC tails HC 6. Each lipid molecule is covalently linked 6. • • • • • • To molecule next to it To the molecule in the opposite monolayer (by the end carbon) ...
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This note was uploaded on 04/20/2010 for the course BIOL 4064 taught by Professor Dr.reyna during the Fall '09 term at Ouachita Baptist.

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