Cellular Respiration and Metabolism - Napa Valley Lec 7 Fall 2016 Dr. Scott 1 Cellular Respiration and Metabolism Cellular Respiration: Harvesting Energy to form ATP Introducing “The Players” Glucose primary substrate for cellular respiration ATP the “energy currency

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  • Biol 219 Lec 7 Fall 2016 Dr. Scott

    1

    Cellular Respiration and Metabolism

    Cellular Respiration: Harvesting Energy to form ATP

    Introducing The Players

    Glucose primary substrate for cellular respirationATP the energy currency moleculePyruvate end product of glycolysis; branch point between

    aerobic and anaerobic metabolismLactate end product of anaerobic metabolismAcetyl CoA the 2-carbon shuttle; a key intermediate

    in aerobic metabolismNAD+ oxidized coenzyme (also FAD)NADH reduced coenzyme (also FADH2):

    carrier of 2 high-energy electronsO2 the final electron acceptor in aerobic metabolismCO2 end product of aerobic metabolism H2O other end product of aerobic metabolism

    Glucose Oxidation: The Central Metabolic Pathway

    1. Glycolysis

    2. Citric Acid (Krebs) Cycle

    3. Electron Transport Chain

    glucose + 6 O2 6 CO2 + 6 H2O + energy ATPheat

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    Glycolysis1. Energy investment steps:

    input 2 ATP

    2. Cleavage step:6C 2 x 3C

    3. Energy capture steps:Net yield = 2 ATP and 2 NADH (4 high-energy e-)

    X 2

    Summary of Glycolysis

    (Aerobic -requires O2)

    Glucose + 2 ADP + 2 NAD+ 2 Pyruvate + 2 ATP + 2 NADH

    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

    Pyruvate enters the matrix of the mitochondria

    Pyruvate is broken down intoa 2-carbon unit of Acetyl CoA

    Yields 1 NADHand1 CO2 is produced

    Acetyl CoA transfers the 2C unit into the Citric Acid Cycle

    Aerobic Metabolism: Transition from Glycolysis to the Citric Acid Cycle

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    The Citric Acid Cycle 2C unit from Acetyl CoA combines with

    Oxaloacetate (4C) to form Citrate (6C)

    Citrate is oxidizedin a series of stepsback to oxaloacetate

    The Citric Acid Cycle

    High energy electrons are captured in the form of

    reduced coenzymes:3 NADH + 1 FADH2

    2 CO2 areproduced

    1 ATP isformed directly

    Electron Transfer in the Citric Acid Cycle

    NADH and FADH2 carry the high-energy electrons to the Electron Transport Chain

    High-energy electrons are transferred to NADH and FADH2 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.

    Citric Acid Cycle Highlights

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    The Electron Transport Chain

    3 major protein complexes (I, III, IV) located in the mitochondrial inner membrane NADH donates high-energy electrons to complex I (FADH2 donates further down) Energy released from downhill flow of electrons is captured to form ATP O2 is the final electron acceptor at the end of the E.T.C.

    Chemiosmotic Theory of ATP Synthesis

    Complexes I, III, IV use energy released from electron transfer to pump H+ ionsuphill from the matrix to the intermembrane space.

    Energy is temporarily stored as an electrochemical gradient of H+

    H+ ions move downhill through the ATP synthase, releasing energy ATP synthase uses energy released to phosphorylate ADP to form ATP

    Summary of Glucose Oxidation and ATP Production

    (net 6 H2O)

    24 e-

    ~ 30

    Comparison of Aerobic and Anaerobic Metabolism of Glucose

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    Glycogen Synthesis (Glycogenesis)

    Glycogen is stored mostly in the liver and skeletal muscle

    Glycogen synthesis is stimulated by insulin

    formation of glycogen from glucose for storage

    Glycogenolysis

    Glycogen stored in the liver helps maintain blood glucose homeostasis between meals

    Glycogenolysis in the liver is stimulated by glucagon

    Glycogen stored in muscle is metabolized during activity

    breakdown of glycogen to glucose

    Summary of Glycogen Metabolism Protein Catabolism and Deamination

    H+

    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

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    Protein Catabolism and Deamination

    H+

    Deamination removes the amino group from amino acids.

    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.

    deamination

    hydrolysis

    Summary of Protein Metabolism

    Fat Catabolism (Lipolysis) and Oxidation

    Triglycerides are broken down by hydrolysis into fatty acids + glycerol

    Fatty acids are broken down 2 C at a time by beta oxidation to form Acetyl CoA

    Fat Catabolism (Lipolysis) and Oxidation

    Acetyl CoA transfers 2 C units to the Citric Acid Cycle;(aerobic CO2 + H2O)

    Yields > 2X more energy per gram than carbohydrates

    Excess fat catabolism produces ketone bodieswhich are acidic (lower pH)

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    Lipid Synthesis Acetyl CoA is a key intermediate for both

    lipid catabolism and lipid synthesis Lipid catabolism occurs in mitochondria;

    lipid synthesis occurs in smooth ER.

    Summary of Fat Metabolism

    beta oxidation

    Gluconeogenesis

    Production of glucose from non-carbohydrate sources

    Important after glycogen stores are depleted to maintain glucose supply to the brain

    Gluconeogenesis is stimulated by cortisol (and glucagon)

    Glycogen Metabolism

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    deamination

    hydrolysis

    Protein Metabolism Fat Metabolism

    beta oxidation

    Gluconeogenesis

    Copy right 2010 Pears on Educ ation, Inc .

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