Lecture5BIO115Winter11d2l - BIO115 The Plasma Membrane Dr....

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Unformatted text preview: BIO115 The Plasma Membrane Dr. Jessica Pamment Life’s Border: Overview • • • 1. 2. 3. Membrane Structure Membrane Function Types of membrane transport Passive Active Bulk Cell Membranes Cell Membranes • 8 nm thick • Fluid mosaic model of lipids and proteins, all with hydrophobic and hydrophilic regions • Dynamic, fluid structures • Fluidity and function depend on composition • Lipid bilayer is asymmetrical Movement of Phospholipids Movement Lateral movement (∼ 107 times per second) Flip-flop (∼ once per month) Membrane fluidity Fluid Viscous Unsaturated hydrocarbon tails with kinks (b) Membrane fluidity Saturated hydrocarbon tails Primary Functions of Membrane Proteins Primary Cystic Fibrosis • Results from a defective plasma membrane • CF patients have faulty chloride channel • Lack of chloride outside cells results in mucus buildup • Mucus becomes site for bacterial infections • Average CF patient lives to age 37 Cystic Fibrosis Transport Mechanisms Transport Mechanisms • Passive Transport­ No energy requirement (includes both simple and facilitated diffusion). • Active Transport­ energy require Diffusion Diffusion • The movement of molecules or ions from a region of their higher concentration to a region of their lower concentration • Equilibrium is reached when the molecules moving in one direction is equal to the molecules moving in the opposite direction Diffusion of one solute Molecules of dye Membrane (cross section) WATER Net diffusion Net diffusion Equilibrium Diffusion of two solutes Net diffusion Net diffusion Net diffusion Net diffusion Equilibrium Equilibrium Selective Permeability of Selective Permeability of Membrane • Hydrophobic molecules can cross through membrane unaided • Hydrophilic molecules and ions need help to get through hydrophobic region • Selective permeability depends on a discriminating lipid bilayer and specific transport proteins Osmosis Osmosis • The diffusion of water across a selectively permeable membrane • Crucial to organisms • Animals in a hypertonic or hypotonic environment require adaptations for osmoregulation Hypotonic solution Hypertonic solution Isotonic solutions Osmosis Sugar molecule Selectively permeable membrane Osmosis Osmosis Osmosis H2O Selectively permeable membrane Osmosis The Water Balance of Living Cells The Hypotonic solution H2 O (a) Animal Isotonic solution H2 O H2 O Hypertonic solution H2 O cell Lysed H2 O (b) Plant H2 O Normal H2 O Shriveled H2 O cell Turgid (normal) Flaccid Plasmolyzed Plant Turgor Plant Filling vacuole 50 µm Contracting vacuole The contractile vacuole of Paramecium Active Transport Active Transport • Movement of solutes across a membrane against their concentration gradient • Carried out by carrier proteins • Enables cells to maintain internal concentration of small solutes that differ from outside environment Active Transport Active Bulk Transport Bulk Transport • Refers to transport of large molecules across membranes • Two main mechanisms: 1. Exocytosis 1. Endocytosis Synthesis of Membrane Membrane Components Secretory protein Glycolipid Golgi 2 apparatus ER 1 Transmembrane glycoproteins 3 4 Summary of Cell Membrane Summary of Cell Membrane • 8 nm thick • Lipid, protein and carbohydrate components • Fluid mosaic model • Membranes are asymmetric • Membranes exhibit selective permeability Summary of Membrane Summary of Membrane Transport • Hydrophobic substances can cross by passive or facilitated diffusion • Hydrophilic substances can pass through • Diffusion of water is known as osmosis channel or carrier proteins by facilitated diffusion Summary of Membrane Transport • Active transport requires energy to move substances across a membrane • Carrier proteins are responsible for active transport • Bulk transport across membrane occurs by exocytosis and endocytosis Bulk Transport by Exocytosis and Endocytosis Bulk BIO115 The Working Cell Jessica Pamment Overview • Energy and the laws of thermodynamics • ATP and cellular work • Enzymes Laws of Thermodynamics • 1st Law: Energy can be transformed and transferred but it can’t be destroyed. Energy is conserved • 2nd Law: Energy transfer always results in a greater amount of disorder (entropy) in the universe The Laws of Thermodynamics Govern Energy Transformations in Organisms Heat Chemical energy CO2 + H2O (a) First law of thermodynamics (b) Second law of thermodynamics Forms of Energy • Energy is the capacity to do work • Kinetic energy: energy in motion • Potential energy: stored energy. • E.g. Chemical energy: energy that matter possesses due to stored energy in bonds of atoms and molecules Potential Energy in Water Behind a Dam Dam Energy Conversion during a dive Energy Entropy Entropy • Entropy is a measure of disorder, of randomness • Every time energy is converted from one form to another, entropy increases • Heat released during energy conversions is main cause of entropy increase Entropy Chemical Energy Chemical Energy • Form of potential energy • Found in matter due to arrangement of atoms • Living cells are able to make chemical energy stored in their food available for work Energy Conversions in a car Energy 25% of fuel energy converted to car’s movement Energy Conversions in a cell Energy 40% of food energy converted to useful work Food Calories Food Calories • Calories are units of energy • 1 Cal is the amount of energy needed to raise the temperature of 1 Kg (=1L) of water by 1oC • Kilocalories (1 kcal=1 C=1000 cal) used to describe energy content of food ATP • Powers cellular work. Stores energy from food, releasing it when required cellular work • ATP the ‘middleman’ between food and ATP is the mediator of all work in the cell ATP Structure ATP Structure • Adenosine triphosphate: adenosine + 3 phosphate groups • Phosphate tail contains stored energy • Loss of a phosphate group releases energy ATP Power Energy stored and Energy Released Glycogen molecule Energy in Anabolic reaction is endergonic Glucose molecules Energy out Catabolic reaction is exergonic The ATP Cycle The Enzymes • Metabolism= the sum of all the chemical reactions (anabolic + catabolic) in an organism • Most metabolic reactions won’t take place without the help of enzymes • Enzymes facilitate nearly every chemical process that takes place in living things Enzymes • Enzymes act as biological catalysts by lowering the energy activation barriers required for metabolic reactions to take place investment in energy required to start a reaction • Activation energy (E ) is the initial A Activation Energy Activation Energy • Is the energy required to start a chemical reaction • It is energy need to break chemical bonds in the reactant molecules, and thus activate them Enzymes and Activation Energy Activation energy barrier Enzyme Activation energy barrier reduced by enzyme Reactant Energy level Energy level Reactant Products (a) Without enzyme (b) With enzyme Products Activation Energy Activation Energy • Can be thought of a small input that is required to trigger a large output • Like lightning a match around lighter fluid… How an Enzyme Works How How an Enzyme Works How How an Enzyme Works How How an Enzyme Works How Substrate Specificity • Essential to enable thousands of biological reactions to take place simultaneously structure • Specificity of enzymes results from its 3D • Active site: region that binds substrate • As substrate binds, active site changes to result in ‘induced fit’ Induced Fit between an Enzyme and its Substrate Substrate Active site Enzyme (a) (b) Enzyme-substrate complex Factors that affect Enzyme Activity • Substrate concentration • Temperature and pH • Inhibitors Competitive Binding Inhibitors • Selectively inhibit action of specific enzymes • An example of competitive inhibitor is Lipitor Summary • One of the defining features of life is that metabolism is never at equilibrium • Metabolism is the sum of all chemical reactions taking place in an organism apply to all living things • The first two laws of thermodynamics Summary • Enzymes are naturally occurring catalysts • Enzyme activity is regulated by substrate concentration, pH, temperature, and inhibitors ...
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This note was uploaded on 04/26/2011 for the course BIO 115 taught by Professor Pamment during the Winter '11 term at DePaul.

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