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2 CONCEPT: REDOX REACTIONS Redox reaction a chemical reaction that involves the transfer of electrons from one atom to another Oxidation loss of electrons Reduction gain of electrons The combustion of fuels releases energy. Electron carrier molecules capable of accepting electrons, and donating them, as part of electron transport NAD + coenzyme that easily transitions between and oxidized and reduced state, and acts as an electron carrier FADH coenzyme that easily transitions between and oxidized and reduced state, and acts as electron carrier Page 2

3 CONCEPT: REDOX REACTIONS Electron transport chain: a series of molecules that transfer electrons through a series of redox reactions Page 3

4 CONCEPT: CELLULAR RESPIRATION Cellular respiration is a series of metabolic pathways that converts the energy in nutrients into ATP. Aerobic respiration involves oxygen. Aerobic respiration can be broken up into 5 steps: Glycolysis à Pyruvate Oxidation à Citric Acid Cycle à Electron Transport Chain à Oxidative Phosphorylation 1. Glycolysis: glucose (6-C) is broken down into 2 pyruvate (3-C) Supplies electron carriers Generates a small amount of ATP via substrate-level phosphorylation Page 4

5 CONCEPT: CELLULAR RESPIRATION 2. Pyruvate (3-C) is oxidized to acetyl CoA (2-C) Supplies an electron carrier 3. Citric Acid Cycle: acetyl CoA (2-C) combines with oxaloacetate and is fully oxidized Supplies electron carriers Generates an ATP indirectly via substrate-level phosphorylation Page 5

6 CONCEPT: CELLULAR RESPIRATION 4. Electron Transport Chain: electron carriers deposit electrons to power proton pumps Generates ATP indirectly via electrochemical gradient 5. Oxidative Phosphorylation: protons move down their concentration gradient, powering ATP synthase Generates a large amount of ATP via oxidative phosphorylation Page 6

7 CONCEPT: GLYCOLYSIS Glycolysis is a series of 10 biochemical reactions that catabolize glucose. 1 glucose + 2 ATP + 2 NAD + à 2 pyruvate + 4 ATP + 2 NADH Occurs in the cytosol Glycolysis has 2 phases: 1.) 2.) Page 7

8 CONCEPT: GLYCOLYSIS Phosphofructokinase carries out the second phosphorylation, and is a key regulation point. Glycolysis Accounting PRACTICE: Glycolysis ATP NADH FADH2 Start Molecule End Molecule Page 8

9 CONCEPT: PYRUVATE OXIDATION Pyruvate moves from the cytosol to the mitochondrial matrix. The pyruvate dehydrogenase complex removes a fully oxidized carbon, and transfers coenzyme A to the molecule. NAD+ is reduced to NADH NADH provides negative feedback to pyruvate dehydrogenase. Page 9

10 CONCEPT: CITRIC ACID CYCLE The citric acid cycle is a series of reactions that take place in the mitochondrial matrix. The citric acid cycle has four phases: 1. Citrate synthesis: acetyl CoA combines with oxaloacetate to form citrate 2. Decarboxylation: series of reactions that reduce 2 NAD +, and result in the loss of 2 CO2 3. Phosphorylation: GTP is synthesized via substrate-level phosphorylation, in some cells it is then used to form ATP 4. Regeneration: final reactions of the cycle that regenerate oxaloacetate, reduce 1 NADH, and reduce 1 FADH2 Generates 3 NADH, 1 FADH2, and 1 ATP/GTP for each acetyl CoA Page 10

11 CONCEPT: CITRIC ACID CYCLE Citrate synthase synthesizes citrate from acetyl CoA and oxaloacetate. Citrate synthase is negatively regulated by ATP. The enzymes which catalyze the reactions resulting in the loss of CO2 are negatively regulated NADH. ATP negatively regulates the enzyme of the second reaction. Phosphofructokinase is regulated by ATP, ADP, and citrate. Page 11

12 CONCEPT: CITRIC ACID CYCLE PRACTICE: Glycolysis Pyruvate Oxidation Citric Acid Cycle ATP NADH FADH2 Start Molecule End Molecule Page 12

13 CONCEPT: ELECTRON TRANSPORT CHAIN The electron transport chain receives electrons from NADH and FADH2, and passes them through a series of electron donors and acceptors embedded in the inner mitochondrial membrane. The electron transport chain is organized as a series of redox reactions between protein complexes I, II, III, and IV. Most of the compounds involved are proteins with cofactors and prosthetic groups that specialize in redox reactions. Cytochromes have iron-containing heme prosthetic groups. Page 13

14 CONCEPT: ELECTRON TRANSPORT CHAIN Ubiquinone and cytochrome c act as electron shuttles between the complexes. Ubiquinone is a lipid soluble molecule (quinone) and can travel through the inside of the membrane. Ubiquinone picks up electrons from NADH at complex I, and from FADH2 at complex II. Cytochrome c picks up electrons from complex III and delivers them to the final complex. Complexes I, III, and IV act as proton pumps. Complex I pumps H+ from the mitochondrial matrix, into the intermembrane space Complex III pumps H+ from the mitochondrial matrix, into the intermembrane space Complex IV pumps H+, and uses H+ to form water Oxygen is the final electron acceptor, forming water. Page 14

15 CONCEPT: OXIDATIVE PHOSPHORYLATION The proton pumps create an electrochemical gradient that stores energy. ATP synthase uses the proton-motive force from the electrochemical gradient to power ATP synthesis. ATP synthase synthesizes ATP through oxidative phosphorylation. Chemiosmosis is the movement of H + ions across the membrane, with their electrochemical gradient. Page 15

16 CONCEPT: OXIDATIVE PHOSPHORYLATION ATP Accounting PRACTICE: Glycolysis Pyruvate Oxidation Citric Acid Cycle ETC Oxidative Phosphorylation ATP NADH FADH2 Start Molecule End Molecule Page 16

17 BIOLOGY - CLUTCH CONCEPT: ANAEROBIC RESPIRATION Some organisms perform anaerobic respiration, using something other than oxygen as the final electron acceptor. Obligate anaerobes oxygen is toxic Facultative anaerobes can perform respiration with or without oxygen Sulfur bacteria use sulfate (SO4-) as their final electron acceptor, forming H2S. Methanogens use CO2 as their final electron acceptor, forming CH4. Page 17

18 CONCEPT: FERMENTATION Fermentation allows glycolysis to continue in the absence of respiration, by regenerating NAD+. Alcohol fermentation pyruvate is converted to ethanol, releasing CO2 and oxidizing NADH Lactic acid fermentation pyruvate is reduced directly by NADH Page 18

19 CONCEPT: METABOLIC CROSSROADS Glycolysis and the citric acid cycle are a crossroads for many metabolic pathways. Proteins can be deaminated and converted to acetyl CoA, pyruvate, and intermediates of the citric acid cycle. Fats can be broken into glycerol and fatty acids. Glycerol can be converted to G3P. Fatty acids can undergo beta-oxidation to become acetyl CoA. Page 19