Chapter 3 (Part 2) - Energy PDF

Energy Chapter 3 (Part 2) ATP ATP = adenosine triphosphate Compound that serves as the primary direct energy source for cellular activities Synthesized from adenosine diphosphate (ADP) + inorganic phosphate (Pi) ATP Synthesis 1) Substrate-level phosphorylation: phosphate group is transferr...

Energy Chapter 3 (Part 2) ATP ATP = adenosine triphosphate Compound that serves as the primary direct energy source for cellular activities Synthesized from adenosine diphosphate (ADP) + inorganic phosphate (Pi) ATP Synthesis 1) Substrate-level phosphorylation: phosphate group is transferred from a metabolic intermediate to ADP to form ATP 2) Oxidative phosphorylation: ADP binds with a free inorganic phosphate to form ATP Requires the electron transport system (in mitochondria) + oxygen ATP Breakdown ATP is a temporary energy store Eventually is broken down to release energy (ATP hydrolysis) Released energy is used to perform work or an endergonic reaction Central Reaction of Energy Metabolism: Glucose Oxidation Glucose oxidation is coupled to ATP synthesis in cells The energy released is used to drive the energy-requiring process of ATP synthesis Stages of Glucose Oxidation 1) Glycolysis Cytosol 2) The Citric acid cycle (Krebs cycle or tricarboxylic acid (“TCA”) cycle) Mitochondrial matrix 3) Oxidative phosphorylation Across inner mitochondrial membrane Coenzymes: NADH + FADH2 Coenzyme: organic molecules derived from water-soluble vitamins that are needed for the function of particular enzymes Directly participate in enzyme-catalyzed reactions by transporting hydrogen atoms and small molecules from one enzyme to another NAD: derived from niacin (vitamin B3); electron carrier FAD: derived from riboflavin (vitamin B2); electron carrier  Glycolysis Occurs in cytosol Each glucose molecule (6 carbons) gets split into two molecules of pyruvate (3 carbons) For each glucose consumed: Net synthesis of two molecules of ATP Two molecules of NADH are produced Summary of Glycolysis The Linking Step (between Glycolysis and the Citric Acid Cycle) Occurs in the mitochondrial matrix Pyruvate is converted to acetyl CoA → the initial substrate for the Krebs cycle Reaction reduces NAD+ to NADH + H+ and produces a To Citric acid cycle/Krebs cycle carbon dioxide For one mole of glucose: Citric Acid Cycle /Krebs Cycle Occurs in mitochondrial matrix For each acetyl CoA: 2 CO2 1 ATP 4 reduced coenzymes 3 NADH + H+ 1 FADH2 (Remember that each glucose molecule that goes through glycolysis will yield 2 acetyl CoA) Summary of the Citric Acid Cycle/Krebs Cycle Summary of Glycolysis & Citric Acid Cycle ATP: Net production of 4 ATP (2 in Glycolysis + 2 in Citric acid cycle) Reduced coenzyme molecules that go to the electron transport chain: 2 molecules of NADH are produced in Glycolysis 2 molecules of NADH are produced in the Linking Step 6 molecules of NADH and 2 molecules of FADH2 are produced in the Citric acid cycle CO2 2 molecules of CO2 are produced in the Linking Step 100% of the 6 CO2 molecules that are produced by glucose 4 molecules of CO2 are produced in the Citric acid cycle oxidation Oxidative Phosphorylation Occurs across inner mitochondrial membrane Most ATP is produced during this step Two simultaneous processes: 1) Electron Transport Chain (releases energy) 2) Chemiosmotic coupling mechanism (use of this energy to make ATP) The Electron Transport Chain A series of electron carriers and other proteins that bind electrons reversibly and transport them in a definite sequence and direction in the inner mitochondrial membrane Arranged in four complexes The movement of electrons through the chain is an exergonic process → released energy is used to drive ATP synthesis The Electron Transport Chain The reduced coenzymes (NADH and FADH2) carry their electrons to the electron transport chain & release their electrons to components of the chain that function as electron acceptors. Electrons move through the chain from one electron acceptor to the next → exergonic process The final electron acceptor is oxygen The protons (H+) are not transported through the chain with the electrons Oxidized forms of the coenzymes (NAD+ and FAD) are regenerated by the chain. Chemiosmotic Coupling Process that couples electron transport to ATP synthesis The energy released in the electron transport chain is used to pump protons (H+) across the mitochondrial membrane (from the mitochondrial matrix into the intermembrane space) against their concentration gradient → Occurs in the first three complexes → The energy stored in this H+ gradient is used to make ATP Chemiosmotic Coupling The concentration gradient favors H+ diffusion back into the matrix, which can only occur through the fourth complex of the electron transport system: ATP synthase. H+ diffusion releases energy ATP synthase harnesses this energy to drive the phosphorylation of ADP → ATP Summary of Oxidative Phosphorylation For every molecule of glucose oxidized, 10 NADH and 2 FADH2 molecules are generated: (10 NADH x 2.5 ATP/NADH) + (2 FADH2 x 1.5 ATP/FADH2) ____________________________________________________________________________________________________________________________________________________________________ 28 ATP Summary of Glucose Oxidation Role of Oxygen in Aerobic Metabolism Oxygen is the final electron acceptor in oxidative phosphorylation Oxygen must be continually supplied to tissues for aerobic metabolism to continue Without oxygen, all electron carriers and the coenzymes NADH and FADH2 will remain in their reduced state. → If oxygen concentration approaches zero, only anaerobic metabolism can continue Anaerobic Conditions Anaerobic metabolism: Conversion of pyruvate to lactate maintains a steady supply of NAD+ for glycolysis to continue, even when oxygen is not available for the citric acid cycle and oxidative phosphorylation to continue Only 2 ATP molecules are produced per glucose in glycolysis Uses of Different Energy Sources Glycogen Metabolism Excess glucose is stored as glycogen (“glycogenesis”) Glycogen can be broken down by glycogenolysis → provides glucose to cells during fasting or when glucose is being rapidly consumed Liver glycogen can be broken down to release glucose into the blood → important for CNS Gluconeogenesis Formation of new glucose from noncarbohydrate-precursors Occurs in the liver Used to provide glucose to CNS Sources: 1) Glycerol (from breakdown of triglycerides) 2) Lactate 3) Amino acids Fat Metabolism Lipolysis: separation of fatty acids from the glycerol molecule Glycerol enters glycolysis as an intermediate Fatty acids are catabolized to acetyl CoA molecules (by beta oxidation) → Krebs cycle Excess breakdown can lead to production of ketones, which can be used by nervous system as a partial alternative to glucose Protein Metabolism Proteolysis: proteins are broken down to amino acids Deamination produces keto acids: Pyruvate Acetyl CoA Citric acid cycle intermediate Enter into the linking step or the citric acid cycle