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Lecture 1 Outline (Ch.5) - Membrane Structure, Permeability, and Transport Across Membranes

This lecture outlines the structure of cell membranes, including the fluid mosaic model, membrane proteins, and membrane fluidity. It also discusses different types of transport across membranes, including passive, facilitated, active, and bulk transport, as well as the role of energy in these processes.

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Lecture 1 Outline (Ch.5) - Membrane Structure, Permeability, and Transport Across Membranes

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  1. محمدحسین ارشد رودی

  2. Lecture 1 Outline (Ch. 5) I. Membrane Structure II. Permeability III. Transport Across Membranes A. Passive B. Facilitated C. Active D. Bulk

  3. Membrane structure 1915, knew membrane made of lipids and proteins • Reasoned that membrane = bilayer Where to place proteins? Lipid layer 1 Proteins Lipid layer 2

  4. Membrane structure

  5. Membrane structure • freeze fracture • proteins intact, one layer or other • two layers look different

  6. Membrane structure Experiment to determine membrane fluidity: • marked membrane proteins mixed in hybrid cell

  7. Membrane structure Membrane fluidity • phospholipid f.a. “tails”: saturation affects fluidity • cholesterol buffers temperature changes

  8. Membrane structure “fluid mosaic model” – 1970s • fluid – phospholipids move around • mosaic – proteins embedded in membrane

  9. Membrane structure • cell membrane – amphipathic - hydrophilic & hydrophobic hydrophilic hydrophobic hydrophilic • membrane proteins inserted, also amphipathic

  10. Membrane Proteins Membrane proteins: Integral: inserted in membrane - transmembrane – span membrane Peripheral: next to membrane - inside or outside

  11. Membrane structure • Two transmembrane proteins: different structure Bacteriorhodopsin: proton pump Bacterial pore protein

  12. Membrane Proteins

  13. Movement of molecules Simple Diffusion: most basic force to move molecules • Disperse until concentration equal in all areas

  14. Movement of molecules Cell membranes only allow some molecules across w/out help: • Small, non-polar molecules OK ex. steroids, O2, CO2 • No charged, polar, or large molecules ex. sugars, ions, water*

  15. Transport Across Membranes • Types of transport: • Passive transport • - Simple diffusion • - Facilitated diffusion • - Osmosis • B. Active transport • C. Bulk transport • Energy Required? • Directionality?

  16. Passive Transport - Simple Diffusion • NO ENERGY required - non-polar molecules (steroids, O2, CO2) • DOWN concentration gradient • molecules equally distribute across available area by type

  17. Passive Transport – Facilitated Diffusion • NO ENERGY required • DOWN concentration gradient • molecules equally distribute but cross membrane with the help of a channel (a) or carrier (b) protein.

  18. Passive Transport - Osmosis • osmosis – movement of water across cell membrane • water crosses cell membranes via special channels called aquaporins • moves into/out of cell until solute concentration is balanced

  19. Passive Transport - Osmosis In each situation below, does water have net movement, and which direction: fewer solutes in solution, than in cell equal solutes in solution as in cell more solutes in solution, than in cell

  20. animal cell plant cell Passive Transport - Osmosis • tonicity – # solutes in solution in relation to cell - hypotonic – fewer solutes in solution - isotonic – equal solutes in solution - hypertonic – more solutes in solution

  21. Passive Transport - Osmosis Paramecium example • regulate water balance • pond water hypotonic • water into contractile vacuole – water expelled

  22. Passive Transport - Osmosis Scenario: in movie theater, watching a long movie. You are: drinking water What happens to your blood? You are: eating popcorn What happens to your blood?

  23. Active Transport • Ex. Na-K ion pump • ENERGY IS required - Na+ ions: inside to out • UP/AGAINST concentration gradient - K+ ions: outside to in • transport proteins a. ion pumps (uniporters) • antiporter: two molecules move opposite directions (UP gradient) b. symporter/antiporter c. coupled transport

  24. Active Transport - uniporter • Ex. proton (H+) pump • ATP used pump H+ ions out • uniporter: ONE molecule UP gradient • against concentration and charge gradients *gradients – used by cell for energy potential

  25. Active Transport – coupled transport • coupled transport: one molecule UP gradient & other DOWN gradient (opposite directions) • Ex. Active glucose transporter • Na+ diffusion used for glucose active transport • Na+ moving DOWN concentration gradient • Glucose moving UP concentration gradient

  26. Bulk Transport • ENERGY IS required • Several or large molecules • Molecules moved IN - endocytosis • phagocytosis – “food” in • pinocytosis – water in

  27. Bulk Transport • receptor-mediated endocytosis – proteins bind molecules, vesicles inside • Molecules moved OUT - exocytosis

  28. Self-Check

  29. Lecture 1 Outline (Ch. 6) • I. Energy and Metabolism • II. Thermodynamics • A. 1st Law – conservation of energy • B. 2nd Law - entropy • Free Energy • Chemical Reactions • V. Cellular Energy - ATP • VI. Enzymes • A. Function • B. Regulation

  30. Energy What is Energy? The capacity to cause change Where does energy on earth come from originally? 40 million billion calories per second!

  31. Metabolism Metabolism –chemical conversions in an organism Types of Energy: - thermal - Kinetic Energy = energy of movement - Potential = stored energy - chemical

  32. Thermodynamics Potential Energy Kinetic Energy Thermodynamics – study of energy transformation in a system Potential energy can be converted to kinetic energy (& vice versa)

  33. Thermodynamics Laws of Thermodynamics: Explain the characteristics of energy • 1st Law: • Energy is conserved • Energy is not created or destroyed • Energy can be converted (Chemical  Heat) 2nd Law: • During conversions, amount of useful energy decreases • No process is 100% efficient • Entropy (measure of disorder) is increased Energy is converted from moreuseful to less useful forms

  34. Metabolism Metabolic reactions: Chemical reactions in organism Two Types of Metabolic Reactions: • Anabolic = builds up molecules Catabolic = breaks down molecules

  35. Chemical Reactions • Chemical Reactions: • Like home offices – tend toward disorder

  36. Chemical Reactions • Chemical Reactions: • Endergonic – energy required to complete reaction • Exergonic – energy given off Exergonic Endergonic

  37. Chemical Reactions + + Reactants Products • Chemical Reaction: • Process that makes and breaks chemical bonds • Two Types of Chemical Reactions: • 1) Exergonic = releases energy • 2) Endergonic = requires energy

  38. Chemical Reactions • 1. Exergonic reactions: “Energy out” • Reactants have more energy than products • Reaction releases energy • 2. Endergonic reactions: “Energy in” • Products have more energy than reactants • Requires influx of energy

  39. Chemical Reactions Glucose  CO2 + H20 CO2 + H20 Glucose release free energy intake free energy spontaneous non-spontaneous • Exergonic reaction • Endergonic reaction

  40. Chemical Reactions Nucleus Nucleus Repel Activation Energy Activation Energy Nucleus Nucleus Repel Activation Energy: Energy required to “jumpstart” a chemical reaction • Must overcome repulsion of molecules due to negative • charged electrons

  41. Chemical Reactions “Downhill” reactions • Exergonic Reaction: • Reactants have more energy than products • But will sugar spontaneously burst into flames? Activation energy: Make sugar and O2 molecules collide sugar + O2 water + CO2

  42. Cellular Energy - ATP • ATP = adenosine triphosphate • ribose, adenine, 3 phosphates • last (terminal) phosphate - removable

  43. ATP + H2O ADP + Pi Cellular Energy - ATP • ATP hydrolyzed to ADP • stores 7.3 calories per mole • Energy released, coupled to another chemical reaction

  44. Cellular Energy - ATP • ATP regenerated • need 7.3 kcal/mol to build ATP • cells power building ATP by coupling to exergonic reactions - cellular respiration

  45. Enzymes Energy of activation (EA) • reactants – absorb energy called: EA • Reach EA, reaction proceeds (limiting step) Exergonic – energy given off • EA from ambient heat usually insufficient • This is GOOD!

  46. -do not make endergonic exergonic Enzymes Enzymes • lower EA • only for specific rxns • cell chooses which reactions go forward! enzymes: -do speed up rxn would occur anyway

  47. Enzymes • enzyme – specific to substrate • active site – part of enzyme -substrate • binding tightens fit – induced fit • form enzyme-substrate complex • catalytic part of enzyme: converts reactant(s) to product(s)

  48. Enzymes

  49. Enzymes • Enzymes lowers EA by: -template orientation -stress bonds • substrate(s) enter -microenvironment • enzyme reused • products formed • What factors might affect enzyme activity?

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