Chap 3-13-14 lecture

Chap 3-13-14 lecture - Essential Cell Biology Third Edition...

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Unformatted text preview: Essential Cell Biology Third Edition Chapters 3, 13, 14 How cells obtain energy from food Copyright © Garland Science 2010 Metabolism: all of the chemical reactions that occur in a cell • thousands of reactions • organized into pathways • interconnected • very complex • two major kinds of pathways: catabolic and anabolic Figure 13-19 Essential Cell Biology (© Garland Science 2010) Metabolic pathway • series of enzyme-catalyzed reactions in which a reactant is converted into a product • product of the first reaction is the reactant for the next Figure 3-1 Essential Cell Biology (© Garland Science 2010) catabolic pathways: release energy and building blocks for making other molecules Figure 3-2 Essential Cell Biology (© Garland Science 2010) anabolic pathways: use energy and building blocks to make other molecules Photosynthesis and respiration are complementary processes • the products of photosynthesis are the initial reactants for respiration and vice versa Figure 3-9 Essential Cell Biology (© Garland Science 2010) Carbon cycle Figure 3-10 Essential Cell Biology (© Garland Science 2010) FREE ENERGY AND CATALYSIS • There are two kinds of chemical reactions with regard to energy Spontaneous vs non-spontaneous reactions Spontaneous reactions • reactants have more energy than the products • energy is released • disorder increases • negative change in free energy (ΔG < 0) Non-spontaneous reactions • reactants have less energy than the products • energy is absorbed • disorder decreases • positive change in free energy (ΔG > 0) Figure 3-16 Essential Cell Biology (© Garland Science 2010) Energetically unfavorable reactions can only occur if they are coupled to energetically favorable reactions • The overall ΔG for the combined reactions is negative and therefore the combined reactions are now spontaneous • coupling mechanisms require enzymes Figure 3-17 Essential Cell Biology (© Garland Science 2010) FREE ENERGY AND CATALYSIS • Enzymes Lower the Energy Barriers That Prevent Chemical Reactions from Occurring Enzymes • enzymes lower the activation energy of the reaction • enzymes bind to substrate(s) and hold them in a particular orientation that reduces the energy needed to facilitate a specific chemical interaction between them • enzymes increase the rate of chemical reactions • enzymes are not consumed in the reactions Figure 3-1 Essential Cell Biology (© Garland Science 2010) Enzymes • enzymes are specific for their substrates Figure 3-15 Essential Cell Biology (© Garland Science 2010) Coupled chemical reactions: mechanical analogy • in cells, enzymes perform the role of the paddle wheel • enzymes store energy in the chemical bonds of activated carrier molecules Figure 3-30 Essential Cell Biology (© Garland Science 2010) Chemical reactions are coupled using activated carrier molecules • these activated carrier molecules contain energy-rich covalent bonds • examples: ATP, NADH, NADPH, acetyl CoA ATP carries a high energy phosphate NADH and NADPH carry high energy electrons acetyl CoA carries a high energy acetyl group Coupled reactions ATP NADH Figure 3-29 Essential Cell Biology (© Garland Science 2010) Synthesis of ATP high energy linkages ATP hydrolysis Figure 3-31 Essential Cell Biology (© Garland Science 2010) ATP • the energetically favorable reaction of ATP hydrolysis is coupled to many different energetically unfavorable reactions in a cell • energy stored in ATP is often harnessed to join two molecules together (condensation reaction) • these reactions often involve the transfer of the terminal phosphate in ATP to another molecule (phosphorylation) Phosphorylation reaction terminal phosphate can be readily transferred to other molecules Figure 3-32 Essential Cell Biology (© Garland Science 2010) Condensation reaction A-H + B-OH A-B + H2O (unfavorable reaction) Cells use an indirect pathway involving ATP 1. B-OH + ATP B-O-PO3 + ADP (favorable reaction) 2. A-H + B-O-PO3 A-B + Pi (favorable reaction) Net: B-OH + ATP + A-H A-B +ADP+Pi +H2O B-O-PO3 is a high energy intermediate • this type of reaction is important for DNA and protein synthesis Condensation reaction high-energy phosphorylated intermediate Figure 3-33a Essential Cell Biology (© Garland Science 2010) Biosynthesis of the amino acid glutamine transfer of a phosphate from ATP activates an intermediate Figure 3-33b Essential Cell Biology (© Garland Science 2010) activation and condensation steps occur on the surface of the same enzyme (glutamine synthase) Figure 3-39 Essential Cell Biology (© Garland Science 2010) Nucleoside triphosphate hydrolysis is coupled to the synthesis of biological polymers Food molecules are broken down in a controlled stepwise fashion to provide useful chemical energy in the form of activated carriers (ATP, NADH) enzymes control each step Figure 13-1 Essential Cell Biology (© Garland Science 2010) ATP, NADH Cells make ATP in two ways: 1. Glycolysis: a. does not require O2 b. occurs in the cytosol 2. Citric acid cycle + electron transport chain: a. requires O2 b. occurs in the mitochondria Food molecules are broken down in three stages 1. Breakdown of large macromolecules into simple subunits (largely outside of cells) 2. Breakdown of simple subunits to acetyl CoA a. produces only a small amount of ATP and NADH b. occurs mainly in cytosol (glycolysis: glucose to pyruvate) c. final step (pyruvate to acetyl CoA) occurs in mitochondria 3. a. b. c. Complete oxidation of acetyl CoA to H2O and CO2 produces lots of ATP and NADH occurs in mitochondria requires O2 (citric acid cycle + electron transport chain) Figure 13-2 Essential Cell Biology (© Garland Science 2010) Stage 2: Glycolysis glucose (6C) two pyruvate (3C) • requires an input of 2 ATP molecules • produces 4 ATP molecules + 2 NADH • net result: 2ATP, 2NADH, 2 pyruvate • occurs in the cytosol; does not require O2 Glycolysis Figure 13-3 Essential Cell Biology (© Garland Science 2010) Stage 2: pyruvate acetyl CoA • pyruvate (3C) is moved from the cytosol to the mitochondria matrix • pyruvate is converted to acetyl CoA (activated carrier molecule) Figure 13-8b Essential Cell Biology (© Garland Science 2010) Figure 13-10 Essential Cell Biology (© Garland Science 2010) Stage 3: citric acid cycle • one turn of the cycle produces: 3 NADH (high energy electrons) 1 GTP 1 FADH2 2 CO2 • there are two turns of the cycle per one glucose molecule • occurs in mitochondria • requires O2 Citric acid cycle Figure 13-11 Essential Cell Biology (© Garland Science 2010) Figure 13-17 Essential Cell Biology (© Garland Science 2010) Stage 3: electron transport chain + oxidative phosphorylation Figure 13-18 Essential Cell Biology (© Garland Science 2010) Stage 3: Electron transport chain • membrane-based mechanism for making ATP • consists of two linked steps: step 1: electron transport chain (a series of electron carriers embedded in the inner mitochondrial membrane) step 2: protein complex called ATP synthase Figure 14-1 Essential Cell Biology (© Garland Science 2010) Mitochondria Figure 14-4 Essential Cell Biology (© Garland Science 2010) Electron transport chain • NADH and FADH2 transfer their high-energy electrons to components of the electron transport chain • as the electrons are passed between these electron acceptor and donor molecules, they fall to lower and lower energy states • energy released at each step is used to pump H+ across the inner membrane creating a proton gradient • the final electron acceptor is O2 Figure 14-6 Essential Cell Biology (© Garland Science 2010) Oxidative phosphorylation • the proton gradient created by the electron transport chain is used to make ATP • H+ flow back down against their electrochemical gradient through a protein complex (embedded in the inner mitochondrial membrane) called ATP synthase • ATP synthase catalyzes the synthesis of ATP from ADP and Pi • this chemiosmotic mechanism is termed oxidative phosphorylation since O2 is consumed (it is the final electron acceptor) and a phosphate group is added to ADP Figure 14-7 Essential Cell Biology (© Garland Science 2010) Figure 14-8 Essential Cell Biology (© Garland Science 2010) Electron transport chain Figure 14-9 Essential Cell Biology (© Garland Science 2010) Video on electron transport chain Table 14-1 Essential Cell Biology (© Garland Science 2010) ...
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