Metabolism: Fueling Cell Growth Principles of Metabolism Cells (including your own) must: Synthesize new components (anabolism/biosynthesis) Harvest energy and convert it to a usable form (catabolism) Principles of Metabolism The role of ATP energy currency Adenosine triphosphate 1
Principles of Metabolism The role of ATP energy currency Principles of Metabolism Harvesting energy - Oxidation of the chemical energy source releases energy (ex. glucose CO 2 ) Oxidation/reduction reactions (redox reactions) electron donor electron acceptor OIL Oxidation is loss of electrons RIG Reduction is gain of electrons Principles of Metabolism The role of electron carriers reducing power In redox reactions, protons often follow electrons e - + H + = H 2
Principles of Metabolism The role of electron carriers 12 pairs of electrons (snatched by electron carriers) Glucose 6 CO 2 Passed to the electron transport chain (used to create the proton motive force); ultimately passed to a terminal electron acceptor (such as O 2, making H 2 O) Used in biosynthesis (to reduce compounds) Principles of Metabolism Synthesizing ATP Substrate-level phosphorylation Principles of Metabolism Synthesizing ATP Substrate-level phosphorylation Oxidative phosphorylation - the energy of proton motive force is harvested; chemical energy is used to create the proton motive force (involves an electron transport chain) ATP synthase ADP + P i ATP 3
Principles of Metabolism Synthesizing ATP Substrate-level phosphorylation Oxidative phosphorylation - the energy of proton motive force is harvested; chemical energy is used to create the proton motive force (involves an electron transport chain) Photophosphorylation - the energy of proton motive force is harvested; radiant energy is used to create the proton motive force (involves an electron transport chain) Scheme of Metabolism energy source terminal electron acceptor Glucose (C 6 H 12 O 6 ) + O 2 NADPH ATP (substrate-level phosphorylation) NADH/FADH 2 electron transport chain proton motive force ATP (oxidative phosphorylation) Carbon dioxide (CO 2 ) + H 2 O Scheme of Metabolism energy source terminal electron acceptor Glucose (C 6 H 12 O 6 ) + O 2 Carbon dioxide (CO 2 ) (heat) + H 2 O Carbon dioxide (CO 2 ) + H 2 O Figure 6.23 4
Scheme of Metabolism 5
Glycolysis (aka Embden-Meyerhoff pathway, glycolytic pathway) glucose 2 pyruvate 2 ATP (net gain) 2 spent; 4 made 2 NADH six different precursor metabolites Glycolysis (aka Embden-Meyerhoff pathway, glycolytic pathway) glucose 2 pyruvate 2 ATP (net gain) 2 spent; 4 made 2 NADH six different precursor metabolites Glycolysis (aka Embden-Meyerhoff pathway, glycolytic pathway) glucose 2 pyruvate 2 ATP (net gain) 2 spent; 4 made 2 NADH six different precursor metabolites Pentose phosphate pathway (not pictured) glucose intermediate of glycolysis NADPH (amount varies) two different precursor metabolites 6
Transition step pyruvate (3 C) acetyl CoA (2 C) + CO 2 (twice per glucose) NADH One precursor metabolite TCA cycle (aka Kreb s cycle, citric acid cycle) acetyl CoA (2 C) 2 CO 2 (twice per glucose) ATP 3 NADH FADH 2 two different precursor metabolites 7
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Review Which central metabolic pathway generates the most reducing power? Review How would a bacterium use protein as an energy source? 9
Scheme of Metabolism energy source terminal electron acceptor Glucose + O 2 (C 6 H 12 O 6 ) ATP (substrate level phosphorylation) NADH/FADH 2 electron transport chain proton motive force ATP (oxidative phosphorylation) Carbon dioxide (CO 2 ) +H 2 O Glucose has been oxidized, but where do the electrons go??? 10
Electron Transport Chain of mitochondria Part of figure 3.55 Electron Transport Chain of mitochondria FADH 2 FAD Terminal electron acceptor Electron Transport Chain of mitochondria Creates the proton motive force FADH 2 FAD 11
Electron Transport Chain The Mechanics 2e - 2H + Electron Transport Chain Mitochondrial matrix Intermembrane space (inside) (outside) NADH + H + Hydrogen carrier Electron carrier Hydrogen carrier 2H + Electron carrier Hydrogen carrier 2H + Electron carrier Electron Transport Chain of mitochondria FADH 2 FAD 12
Electron Transport Chain of E. coli Aerobic respiration (shown) Anaerobic respiration NO 3 as a TEA (different ubiquinol oxidase) Quinone used provides humans with vitamin K oxidase test FADH 2 FAD Pathway Eukaryote Prokaryote Glycolysis Cytoplasm Cytoplasm Intermediate step Cytoplasm Cytoplasm TCA cycle Mitochondrial matrix Cytoplasm ETC Mitochondrial inner membrane Plasma membrane Overall Maximum Yield 13
Overall Maximum Yield Overall maximum energy yield of aerobic respiration (ignoring the pentose phosphate pathway): Complete oxidation of glucose 4 ATP 10 NADH Electron transport 2 FADH 2 chain (oxidative phosphorylation) 3 ATP/NADH 2 ATP/FADH 2 Overall Maximum Yield Overall maximum energy yield of aerobic respiration (ignoring the pentose phosphate pathway): Complete oxidation of glucose 4 ATP 10 NADH Electron transport 2 FADH 2 chain (oxidative phosphorylation) 3 ATP/NADH 2 ATP/FADH 2 38 ATP (maximum theoretical) Overall Maximum Yield Overall maximum energy yield of aerobic respiration (ignoring the pentose phosphate pathway): Complete oxidation of glucose 4 ATP 10 NADH Electron transport 2 FADH 2 chain (oxidative phosphorylation) 3 ATP/NADH 2 ATP/FADH 2 4 + 34= 38 ATP (maximum theoretical) 14
Used when respiration is not an option Lack of TEA No electron transport chain Oxidation of glucose stops at pyruvate Fermentation Used when respiration is not an option Lack of TEA No electron transport chain Oxidation of glucose stops at pyruvate Passes electrons from NADH to pyruvate or a derivative Fermentation NAD NADH The logic: Oxidizes NADH, generating NAD for use in further rounds of glucose breakdown Stops short of the transition step and the TCA cycle, which together generate 5X more reducing power 15
Fermentation Fermentation Review 16
Review source versus terminal electron acceptor Glucose + 6 O 2 6 CO 2 + 12 H 2 O Enzymes A specific, unique, enzyme catalyzes each biochemical reaction Enzyme activity can be controlled by a cell Enzymes can be exploited medically, industrially Enzyme names usually reflect the function and end in -ase 17
1/18/2011 Enzymes Enzymes What are allosteric enzymes and why are they important? Enzymes Enzyme inhibition Non-competitive inhibition - Inhibitor/substrate act at different sites Regulation (allosteric) Enzyme poisons (example: mercury) Competitive inhibition - Inhibitor/substrate act at same site Ex.: PABA folic acid coenzyme Sulfa 18
Enzymes Environmental factors influence enzyme activity temperature, ph, salinity Enzymes Cofactors act in conjunction with certain enzymes Coenzymes are organic cofactors 19