Lecture4BIO155BB - BIO155 The Working Cell Jessica Pamment...

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Unformatted text preview: BIO155 The Working Cell Jessica Pamment Overview • Energy and the laws of thermodynamics • ATP and cellular work • Enzymes Laws of Thermodynamics • An organism transforms matter and energy subject to the laws of thermodynamics • 1st Law: Energy can be transformed and transferred but it can’t be destroyed. Energy is conserved • 2nd Law: A system and its surrounding always proceed to a state of maximum entropy (disorder) 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 associated with the relative motion of objects • Potential energy: energy associated with location or arrangement of object. Example is 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 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 gram of water by 1oC • Kilocalories (1000 cal= 1 C= 1 kcal) used to describe energy content of food ATP • • 1. 2. 3. Powers cellular work. Stores energy from food, releasing it when required Cell does three types of work: Chemical work Transport work Mechanical work 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 ATP Drives Mechanical Work ATP (Myosin motors in muscle cell contraction Muscle cell Actin filament Myosin filament Myosin arm ATP Drives Transport Work ATP ATP Drives Chemical Work ATP The ATP Cycle The Enzymes • Metabolism= the sum of all the chemical reactions in an organism • Most metabolic reactions won’t take place without the help of enzymes enzymes • All living cells contain 1000s of different 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… Substrate Specificity • Essential to enable thousands of biological reactions to take place simultaneously structure • Specificity of enzymes results from its 3D Active site is region of enzyme that binds substrate only few amino acids long in ‘induced fit’ • As substrate binds, active site changes to result Induced Fit between an Enzyme and its Substrate Substrate Active site Enzyme (a) (b) Enzyme-substrate complex How an Enzyme Works How How an Enzyme Works How How an Enzyme Works How How an Enzyme Works How Factors that affect Enzyme Activity • Substrate concentration • Temperature and pH • Inhibitors Competitive Binding Noncompetitive Binding Inhibitors • • • 1. 2. Selectively inhibit action of specific enzymes Can be reversible or irreversible inhibition Two type of inhibitors Competitive Noncompetitive 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 • The first two laws of thermodynamics apply to all transformation of matter that take place in living things Summary • Enzymes are naturally occurring catalysts • Enzyme activity is regulated by substrate concentration, pH, temperature, and inhibitors 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 Transport Mechanisms Transport Mechanisms • Passive Transport­ includes both simple and facilitated diffusion. No energy requirement as solutes move down concentration gradient • Active Transport­ requires energy to move solutes against their concentration gradient Diffusion Diffusion • Diffusion is the tendency for molecules to spread into the available space from an area of higher to an area of 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 • Hydrocarbons, CO2 and O2­ 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 surroundings • E.g. Cells have higher [K+] and lower [Na+] than Active Transport Active Bulk Transport Bulk Transport • Refers to transport of large molecules across membranes • Two main mechanisms: 1. Exocytosis 1. Endocytosis i. Phagocytosis ii. Pinocytosis iii. Receptor­mediated endocytosis Bulk Transport Bulk Transport • Refers to transport of large molecules across membranes • Two main mechanisms: 1. Exocytosis 1. Endocytosis i. Phagocytosis ii. Pinocytosis iii. Receptor­mediated endocytosis Phagocytosis Phagocytosis PHAGOCYTOSIS EXTRACELLULAR FLUID CYTOPLASM Pseudopodium 1 µm Pseudopodium of amoeba Bacterium Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM) Pinocytosis Pinocytosis PINOCYTOSIS 0.5 µm RECEPTOR-MEDIATED ENDOCYTOSIS Coat protein Receptor Coated pit Ligand Coat protein A coated pit and a coated vesicle (TEMs) Plasma membrane 0.25 µm Cholesterol Uptake by human cells Cholesterol Cell Signaling Cell Signaling • Cells communicate via signaling across cell membranes • Signal protein binds receptor protein on membrane • Binding triggers signal transduction pathway • Results in chemical responses 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 transport • Carrier proteins are responsible for active • Bulk transport across membrane occurs by exocytosis and endocytosis Bulk Transport by Exocytosis and Endocytosis Bulk BIO155 Cellular Respiration Dr. Jessica Pamment Overview Overview • • • • i. ii. iii. Energy flow; producers and consumers Aerobic respiration: cellular respiration Anaerobic respiration: fermentation Respiratory pathways: Glycolysis Citric Acid Cycle Oxidative Phosphorylation Energy flow and Energy flow and chemical cycling in ecosystems Producer Producer and consumer Autotrophs and Heterotrophs Autotrophs and • Autotrophs are the producers of the biosphere • Autotrophs are self­feeders • Heterotrophs are the consumers of the biosphere • Heterotrophs feed on compounds made by other organisms Cellular Respiration Cellular Respiration • The aerobic harvesting of chemical energy from organic fuel molecules • Oxygen in the air we breathe in is required for cellular respiration • Carbon dioxide is a by product found in the air we exhale How breathing is How breathing is related to cellular respiration Cellular Respiration Cellular REDOX reactions REDOX Redox Reactions Redox Reactions • Reduction­oxidation reactions • Reactions that transfer electrons between reactants • A substrate that gains electrons is said to have been reduced • A substrate that has lost electrons is said to have been oxidized Redox Reaction Redox becomes oxidized (loses electron) becomes reduced (gains electron) Electron Transfer and Energy Electron Transfer and Energy Release • Electrons lose potential energy when moved from a less electronegative atom to a more electronegative atom • Release of energy used for ATP synthesis • Electrons are transferred to oxygen in a stepwise manner Arapid A rapid electron ‘fall’ The role of The role of oxygen in harvesting food energy NAD+ and Electron Transport NAD+ and Electron Transport Chain • Electrons from glucose are stored as potential energy in NADH • Transport chain consists of mainly proteins built into the inner membrane of mitochondria • NADH releases electrons that are passed by a series of redox reactions down the chain until they reach oxygen • Energy is released in a stepwise fashion 3 Stages of Respiration 3 Stages of Respiration • Respiration is a metabolic pathway • 3 main metabolic stages: 1.Glycolysis 2.Citric acid cycle 3.Electron transport The three stages of cellular respiration The three stages of cellular respiration Glycolysis Glycolysis Glycolysis Glycolysis Glycolysis Direct phosphate transfer Glycolysis Glycolysis • Means sugar splitting • Anaerobic process • Takes place in cytosol • One molecule of glucose is converted to two of pyruvate and net two of ATP glucose • Releases less than 25% of chemical energy stored in The Citric Acid Cycle The Citric Acid Cycle • A.K.A Kreb’s Cycle • Takes place in the mitochondrial matrix • Oxidizes organic fuel derived from pyruvate • The cycle generates 1 ATP per turn • Most energy is transferred to NAD+ and FAD+ The link between Glycolysis and the The link between Glycolysis and the Citric Acid Cycle The Citric Acid Cycle The Citric Acid Cycle • Citric acid cycle turns twice for each glucose molecule because two acetic molecules derived from one glucose molecule • 3 CO2 per cycle (6 CO2 per glucose molecule) • 1 ATP per cycle (2 ATPS per glucose molecule) • 3 NADH per cycle (6 NADH per glucose molecule) • 2 FADH2 per cycle (4 FADH2 per glucose molecule) Electron Transport Electron Electron Transport Electron ATP synthase • http://www.youtube.com/watch? v=uOoHKCMAUMc Electron Transport Chain Electron Transport Chain • Takes place in the inner mitochondrial membrane in eukaryotes numbered I to IV electronegative • Components of chain are multiprotein complexes • Complexes arranged in order from less to more • Electrons passed down by redox reactions Electron Transport Chain • Energy released as electrons transferred between complexes used to pump H+ synthases ADP • The proton­motive force drives H+ through ATP • ATP synthase uses flow of H+ to phosphorylate • 1000s of chains found in any one mitochondria Energy Energy from Food Summary of ATP yield during cellular respiration Summary of ATP yield during cellular respiration In the absence of oxygen…. In the absence of oxygen…. • Cells can oxidize organic fuel and 1. Anaerobic respiration 1. Fermentation generate ATP without the use of oxygen: Anaerobic Respiration Anaerobic Respiration • Uses an electron transport chain, but doesn’t use oxygen as final acceptor of electrons • Example of alternative final electron acceptors is sulfate and nitrate ions • ATP synthase uses membrane potential to generate ATP Fermentation Fermentation • A method of harvesting chemical energy without the use of an electron transport chain • Fermentation is an expansion of glycolysis that allows continuous generation of ATP by direct phosphate transfer • A way of regenerating NAD+ from NADH made during glycolysis in the absence of the electron transport chain Lactic Acid Fermentation Lactic Acid Fermentation Alcohol Fermentation Alcohol Fermentation Yeast Yeast Respiration vs. Fermentation Respiration vs. Fermentation Respiration ATP synthesis Oxidation of organic molecs Oxidizing agent Final electron acceptor ATP yield Aerobic Glycolysis NAD+ Oxygen 38 ATPs Fermentation Anaerobic Glycolysis NAD+ Pyruvate 2 ATPs Fermentation vs. Respiration Fermentation vs. Respiration • Both metabolic reactions that produce ATP • Fermentation is the partial degradation of sugar without the use of oxygen • Aerobic Respiration is the breakdown of sugars with the use of oxygen Evolution Connection Evolution Connection • Glycolysis is the most widespread metabolic pathway • Glycolysis takes place in the cytosol, without involvement of organelles • Glycolysis occurs under both aerobic and anaerobic conditions • Suggests it evolved early 0 A Time line of oxygen and life on Earth O present in Earth’s atmosphere Billions of years ago 2.1 2.2 2.7 First eukaryotic organisms Atmospheric oxygen reaches 10% of modern levels Atmospheric oxygen first appears 2 3.5 Oldest prokaryotic fossils Origin of Earth 4.5 Summary Energy Flow Summary Energy Flow Summary of Respiration Summary of Respiration • Main role is to harvest energy from glucose for ATP synthesis chain ATP ATP • Energy flows: glucose NADH electron transport • 40% of potential energy in glucose transferred to • 3 stages: glycolysis, Citric Acid Cycle, electron transport chain Summary Summary • Glycolysis is the first step in harnessing energy from organic compounds • If oxygen is present, pyruvate enters the Citric Acid Cycle and oxidative phosphorylation pathways • If oxygen is absent, pyruvate can be oxidized by a different compound or enter fermentation Summary Summary • Most energy is made by the electron transport chain • Cell uses energy released from organic compounds to power anabolic reactions essential to life ...
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This note was uploaded on 04/25/2011 for the course BIO 155 taught by Professor Skoubis during the Fall '10 term at DePaul.

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