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BIO1140 StudyFest Answer Key 2011

BIO1140 StudyFest Answer Key 2011 - BIO1140 StudyFest 2011...

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BIO1140 StudyFest 2011 Answer Key 1. Name the five functions of the cell membrane. 1. Define boundaries; selectively permeable barrier 2. Localisation and organisation Scaffold for biochemical activities (enzymes) e.g. mitochondria 3. Regulation of solute transport In and out of cell and/or organelles Uphill or downhill e.g. Na + ,K + -ATPase 4. Responses to external signals Receptors and signal transduction e.g. ß-adrenoreceptor 5. Cell-to-cell communication Recognition, adhesion, exchange of materials Gap junctions, plasmodesmata 2. Describe what is meant by the “Fluid Mosaic Model”, and why this is applicable to the cell membrane. Fluid mosaic model: - Lipid-protein assembly in which components are held together in a thin sheet by non-covalent bonds - Two fluid lipid layers – structural backbone, permeability barrier - Mosaic of proteins – unique complement responsible for specific functions 3. What are some of the key components of the “unit membrane” (Gorter and Grendel, 1925)? Composition Phosphoglycerides serine, choline, ethanolamine, inositol 16-18 C saturated & unsaturated Glycolipids single sugars or oligosaccharides marker (e.g. ABO blood groups) Sterols Cholesterol, phytosterols Absent from prokaryotes
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Variable 4. What features of the cell membrane allow for increased fluidity (even when temperatures are decreased)? Membrane fluidity Fluid nature of membrane essential for function As temperature increases, fluidity increases C chain length and saturation Head group polarity Buffering effect of sterols Homeoviscous adaptation Alterations in lipid composition to maintain membrane fluidity at different environmental temperatures 5. What are the three types of membrane proteins and how are they attached to the cell membrane? i. Integral membrane proteins Amphipathic with one or more hydrophobic regions Usually transmembrane (single or multipass) Transmembrane regions typically a-helix of 20-30 hydrophobic aa residues ii. Peripheral membrane proteins Membrane-associated through non-covalent interactions Dynamic relationship with membrane iii. Lipid-anchored membrane proteins Membrane-associated through covalent linkages to phospholipids Fatty-acid anchored Intracellular orientation GPI anchor (glycosylphosphatidylinositol) extracellular orientation can be cleaved with phospholipase C e.g. type IV carbonic anhydrase
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6. What kinds of molecules can get across the cell membrane easily? What kinds cannot? What are the different types of transportation that allow movement across the cell membrane? How? 1. Passive transport - Simple diffusion - Facilitated diffusion 2. Active transport - Primary -Secondary 7. Describe how passive transport works. For simple diffusion, what gradients regulate the transport of: i. gases ii.ions iii.water Diffusion Spontaneous; based on random movements Driven by diffusion gradient (downhill) For solutes without a charge concentration gradient For gases partial pressure gradient For ions electrochemical gradient
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For water osmotic gradient Facilitated diffusion Channel proteins
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