Biol 219 Lec 7 Fall 2016

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1 Cellular Respiration: Harvesting Energy to form ATP Cellular Respiration and Metabolism Glucose ATP Pyruvate Lactate Acetyl CoA NAD + Introducing The Players primary substrate for cellular respiration the energy currency molecule end product of glycolysis; branch point between aerobic and anaerobic metabolism end product of anaerobic metabolism the 2-carbon shuttle; a key intermediate in aerobic metabolism oxidized coenzyme (also FAD) NADH reduced coenzyme (also FADH 2 ): carrier of 2 high-energy electrons O2 the final electron acceptor in aerobic metabolism CO2 H2O end product of aerobic metabolism other end product of aerobic metabolism Glucose Oxidation: The Central Metabolic Pathway glucose + 6 O2 6 CO2 + 6 H2O + energy ATP heat 1. Glycolysis 2. Citric Acid (Krebs) Cycle 3. Electron Transport Chain 1

Energy capture steps: Net yield = 2 ATP and 2 NADH (4 high-energy e - ) X 2 Anaerobic Metabolism: The Lactic Acid Pathway Pyruvate is converted to Lactate NADH is converted

2 Glycolysis 1. Energy investment steps: input 2 ATP Summary of Glycolysis Glucose + 2 ADP + 2 NAD + 2 Pyruvate + 2 ATP + 2 NADH 2. Cleavage step: 6C 2 x 3C (Aerobic - requires O2) 3. Energy capture steps: Net yield = 2 ATP and 2 NADH (4 high-energy e - ) X 2 Anaerobic Metabolism: The Lactic Acid Pathway Pyruvate is converted to Lactate NADH is converted back to NAD + which is needed for glycolysis Net yield is 2 ATP Aerobic Metabolism: Transition from Glycolysis to the Citric Acid Cycle Pyruvate enters the matrix of the mitochondria Pyruvate is broken down into a 2-carbon unit of Acetyl CoA Yields 1 NADH and 1 CO2 is produced Acetyl CoA transfers the 2C unit into the Citric Acid Cycle 2

3 The Citric Acid Cycle 2C unit from Acetyl CoA combines with Oxaloacetate (4C) to form Citrate (6C) Citrate is oxidized in a series of steps back to oxaloacetate The Citric Acid Cycle High energy electrons are captured in the form of reduced coenzymes: 3 NADH + 1 FADH2 2 CO2 are produced 1 ATP is formed directly Electron Transfer in the Citric Acid Cycle High-energy electrons are transferred to NADH and FADH2 NADH and FADH2 carry the high-energy electrons to the Electron Transport Chain Citric Acid Cycle Highlights Acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C) Citrate is oxidized in a series of steps back to oxaloacetate High-energy electrons are captured in reduced coenzymes: 3 NADH + 1 FADH2 2 CO2 are produced 1 ATP is formed directly NADH and FADH2 carry high-energy electrons to the Electron Transport Chain where most ATP is produced. 3

The Electron Transport Chain Chemiosmotic Theory of ATP Synthesis Ø 3 major protein complexes (I, III, IV) located in the mitochondrial inner membrane Ø NADH donates high-energy electrons to complex

4 The Electron Transport Chain Chemiosmotic Theory of ATP Synthesis Ø 3 major protein complexes (I, III, IV) located in the mitochondrial inner membrane Ø NADH donates high-energy electrons to complex I (FADH2 donates further down) Ø Energy released from downhill flow of electrons is captured to form ATP Ø O2 is the final electron acceptor at the end of the E.T.C. Ø Complexes I, III, IV use energy released from electron transfer to pump H + ions uphill from the matrix to the intermembrane space. Ø Energy is temporarily stored as an electrochemical gradient of H + Ø H + ions move downhill through the ATP synthase, releasing energy Ø ATP synthase uses energy released to phosphorylate ADP to form ATP Summary of Glucose Oxidation and ATP Production Comparison of Aerobic and Anaerobic Metabolism of Glucose 24 e- (net 6 H2O) ~ 30 4

5 Glycogen Synthesis (Glycogenesis) formation of glycogen from glucose for storage Ø Glycogen is stored mostly in the liver and skeletal muscle Ø Glycogen synthesis is stimulated by insulin Glycogenolysis breakdown of glycogen to glucose Ø Glycogen stored in the liver helps maintain blood glucose homeostasis between meals Ø Glycogenolysis in the liver is stimulated by glucagon Ø Glycogen stored in muscle is metabolized during activity Summary of Glycogen Metabolism Protein Catabolism and Deamination Protein catabolism breaks down proteins into amino acids by hydrolysis of peptide bonds Occurs in the GI tract and within cells in lysosomes and proteasomes H + 5

6 Protein Catabolism and Deamination Deamination removes the amino group from amino acids. Summary of Protein Metabolism hydr olysis deam ination Forms organic acids (keto acids) which enter glycolysis or the Krebs Cycle Amino group is released as NH3 then converted to urea to be excreted in the urine. H + Fat Catabolism (Lipolysis) and Oxidation Fat Catabolism (Lipolysis) and Oxidation Ø Triglycerides are broken down by hydrolysis into fatty acids + glycerol Ø Fatty acids are broken down 2 C at a time by beta oxidation to form Acetyl CoA ØAcetyl CoA transfers 2 C units to the Citric Acid Cycle; (aerobic CO2 + H2O) Ø Yields > 2X more energy per gram than carbohydrates Ø Excess fat catabolism produces ketone bodies which are acidic (lower ph) 6

Lipid Synthesis Ø Acetyl CoA is a key intermediate for both lipid catabolism and lipid synthesis Ø Lipid catabolism occurs in mitochondria; lipid synthesis occurs in smooth ER.

7 Lipid Synthesis Ø Acetyl CoA is a key intermediate for both lipid catabolism and lipid synthesis Ø Lipid catabolism occurs in mitochondria; lipid synthesis occurs in smooth ER. Summary of Fat Metabolism beta oxidation Gluconeogenesis Glycogen Metabolism Ø Production of glucose from non-carbohydrate sources Ø Important after glycogen stores are depleted to maintain glucose supply to the brain Ø Gluconeogenesis is stimulated by cortisol (and glucagon) 7

8 Protein Metabolism Fat Metabolism hydr olysis deam ination beta oxidation Gluconeogenesis Copy right 2010 Pears on Educ ation, Inc. 8

Metabolism. Chapter 5. Catabolism Drives Anabolism 8/29/11. Complete Catabolism of Glucose

Metabolism. Chapter 5. Catabolism Drives Anabolism 8/29/11. Complete Catabolism of Glucose 8/29/11 Metabolism Chapter 5 All of the reactions in the body that require energy transfer. Can be divided into: Cell Respiration and Metabolism Anabolism: requires the input of energy to synthesize large