Meeting 3 & 4

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Meeting 3 & 4
2012-02-23 22:52:23

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  1. aerobic oxidation
    breakdown products of sugar (carbs) or fatty acids (hydrocarbons) [both derived from the digestion of food in animals] are coverted (via OXIDATION) to CO2 and water

    the energy release from this transformation is converted into chemical energy of phosphoanhydride bonds in ATP
  2. Aerobic oxidation has a ΔG = to/of -686 kcal/mol...what does this mean?
    when ΔG is negative, a process or chemical reaction proceeds spontaneously in the forward direction, so this means the breakdown of sugar (glucose/fructose/C6H12O6) and oxygen into CO2 and water leaves the cell/organism with -686 kcal/mol of energy to use, say for oh I don't know, making ATP? cool.
  3. ΔG = ΔH + TΔS
    Free Energy = enthalpy + entropy
  4. 1) when ΔG is negative, a process or chemical reaction proceeds spontaneously in the:

    2) when ΔG is positive, the process proceeds spontaneously in:

    3) when ΔG is zero, the process is:
    1) when ΔG is negative, a process or chemical reaction proceeds spontaneously in the forward direction

    2) when ΔG is positive, the process proceeds spontaneously in reverse

    3) when ΔG is zero, the process is already in equilibrium, with NO net change taking place over time
    • biological systems achieve the best possible match when
    • the delta G’s between 2 reactions are close in number

    aka exergonic reactions should be similar in 'level' to endergonic ones
  5. Catabolism/exergonic rxn
    the set of metabolic pathways that break down molecules into smaller units and release energy (Greek: kata = downward + ballein = to throw)

    exergonic process: one in which there is a positive flow of energy from the system to the surroundings
  6. anabolism/endergonic rxn
    the set of metabolic pathways that construct molecules from smaller units; these reactions require energy

    endergonic: not spontaneous; the system absorbs energy from the surroundings: energy is put into the system.
  7. when you degrade ATP, you get about ΔG°=-7.3kcal/mol, so that means it takes ~7.3 kcal/mol to MAKE ATP

  8. In aerobic respiration, one molecule of glucose yields:
    • 38 ATP molecules
    • -8 produced during glycolysis
    • -6 from the link reaction
    • -24 from the Krebs cycle

    Net gain = 36 ATP; 2 ATP molecules produced from glycolysis are used up in the re-oxidation of the hydrogen carrier molecule NAD
  9. proton-motive force
    the energy stored in the proton electrochemical gradient, that's generated across a membrane driven by energy release as electrons travel through an electron transport chain

    this energy stored in the gradient (proton-motive force) is used directly to power the synthesis of ATP and other energy-requiring processes
  10. I. Glycolysis
    conversion of one 6-carbon glucose molecule to two 3-carbon pyruvate molecules

    • -this happens in the cytosol (so inside the cell, in the cytoplasm)
    • -called anaerobic glucose catabolism b/c no O2 is required
    • -yields a net of of ONLY 2 ATP molecules per glucose molecules b/c of the four created, 2 are used to propell substrate-level phosphorylation
  11. Nicotinamide Adenine Dinucleotide Coenzyme
    when glucose is converted to pyruvate, 4 electrons (e-) and 2 of the 4 protons (H+) are transferred to 2 molecules of the oxidized form of NAD+, making the reduced form NADH

    the energy carrid by the electrons in NADH (and an analogous carrier, FADH2) can be used to make more ATPs via the E.T.C.

    glyceraldehyde 3-phosphate dehydrogenase catalyzes the reduction of NAD+ to NADH
  12. substrate-level phosphorylation
    the generation of four ATP molecules by phosphorylation of four ADPs (different from IV. oxidative phosphorylation that generates ATP in 3rd stage of aerobic oxidation); this one happens within glycolysis?
  13. 3 alosterically controlled enzymes play a role in regulating the glycolytic pathway:
    1) hexokinase: inhibited by the product of its reaction (glucose 6-phosphate); uses ATP to add a phosphate to a 6 ring sugar (hexo=6), turns glucose into glucose 6-phos

    2) pyruvate kinase: occurs at last step of glycolysis; cell senses excess of ATP as a reactant (not product); inhibited by ATP (glycolysis slows down if too much ATP is present); has a

    3) phosphofructokinase-1: controlled by several molecules, the principle rate-limiting enzyme of the glycolytic pathway
  14. phosphofructokinase-1
    • -undergoes positive and negative feedback; activity of enzyme is modulated tightly
    • -negative (inhibition): high ATP/citrate concentration, too much of downstream compound slows down phosphofructokinase-1
    • -activation: high AMP or glycolysis synthesized fructose 2, 6-biphosphate, which propells the activation of enzyme

    essentially: inhibited by ATP and activated by AMP (detects the ratio of compounds); the catalytic site has a greater affinity for ATP than the inhibitory site; so at low concentrations ATP will bind to the catalytic site not the inhibitory site; at high concentrations it binds to both
  15. reducing v. oxidizing agent
    reducing agent (reducer) is the element/compound in a redox reaction that DONATES an electron to another species; b/c the reducer loses an electron it is oxidized

    Oxidizer: an electron recipient

    Thus reducers are "oxidized" and oxidizers are "reduced"
  16. II. Citric Acid Cycle
    • CoA (co-enzyme A, a 2-carbon acetyl intermediate) oxidates the pyruvates (3-carbon) to a CO2 in the mitochondrion
  17. Oxidative decarboxylation
    this happens when pyruvate enters the mitochondrion; it's an oxidation reactions where a carboxylate group is removed, forming carbon dioxide

    • basically pyruvate dehydrogenase (enzyme) converts pyruvate to form one molecule of CO2 and acetic acid
    • -the acetic acid is subsequently is linked to coenzyme A to form acetyl CoA; this happens synchroneously with the reciduction of one NAD+ to NADH

    • -exergonic: conversion of pyruvate to CO2?
    • -endergonic: the reduction of NAD+ (COUPLING)

    the further metabolism of acetyl CoA & NADH makes ~28 ATPs per glucose molecule (oxidized)
  18. acetyl CoA
    main function: to convey the carbonatoms within the acetyl group to the citric acid/Krebs cycle to be oxidized for energy production

    • -enters the krebs cycle
    • -metabolic hub by which long chain of glucoses can enter the krebs cycle
    • -CoA needs to be frequently recycled
  19. oxaloacetate
    C4 acid; couples the acetyl group (ultimately comes form pyruvate) into a citrate (a C6 acid); acetyl CoA is recycled
  20. NET result of citric acid/krebs cycle
    for each acetyl group that enters as CoA:

    • -2 molecules of CO2
    • -3 NADH
    • -1 FADH2
    • -1 GTP

    are produced
  21. thioester bond (in step 6)
    breaking this is an exergonic reaction; can couple with synthesis of GTP (high energy compound)
  22. inner mitochondrial membrane is impermeable to:
    NADH; to bypass this problem electrons fro...490
  23. III. Electron transport
    generates the proton-motive force (energy)
  24. IV. Oxidative Phosphorylation
    ATP synthesis in the mitochondrion
  25. •Oxidation:
    • •Oxidation: loss of electrons (+)
    • •Reduction: gain ofelectrons (-)
    • •Oxidation and reduction are always coupled
  26. all the intermediates between glucose and pyruvate are:
    phosphorylated compounds; also reations with large NEGTAIVE G values means that they're essentially irreversible
  27. study showed: oxidation of NADH by O2 is coupled to the movemen of protons OUT of the matrix

    • -basically experiment put mitochondria in a suspension with NO oxygen, and none of the NADH was oxidized (to NAD+)
    • -when a small about of O2 is added, there's a SHARP rise in H+ concentration in the suspension (means pH drops)
    • -eventually the oxygen is depleted so protons move back into the mitochondria
  28. there are 4 large multiprotein complexes in the ETC that span the inner mitochondrial membrane:
    1) Complex I: NADH-CoQ reductase

    2) Complex II: succinate Co-Q reductase

    3) Complex III: CoQH2-cytochrome c reductase

    4) Complex IV: cytochrome c oxidase

    -each has certain prosthetic groups: small non-peptide organic molecules or metal ions are associated with proteins, but not actual proteins; they move the electrons
  29. electrons from NADH:
    flow from complex, I, III, and IV, SKIPPING complex II
  30. electrons from FADH2
    flow from complex, II, III, and IV, SKIPPING complex I
  31. If for 1 mol of NADH, 10 protons (H+) are translocated, &
    NADH + H+ + ½ O2 -----> NAD+ + H2O
    has a G = -52.6 kcal/mol, then how much energy is 'released' for one (mol of) proton?
    • about 5: energy to translocate one (mol of) proton (~52/10)
    • we're in business
  32. redox potential: measure of the tendency of a chemical species to acquire electrons ake be reduced; the more positive the potential, the greater the species' affinity for e- and more likely it is to be reduced

    So: e- transfer between NADH and Oxygen
    • NADH ---> NAD+ + H+ + 2e-
    • -this rxn has a - redox potential (-320mV), meaning it is energetically favorable for e- to leave NADH

    • 2H+ +2e- +½O2 ----> H2O
    • -this rxn has a + redox potential (816mV), meaning its energetically favorable for O2 to gain e-

    • -low redox potential LOSE electrons, HIGH gains electrons
    • -either way here, what both molecules are experiencing is energetically + (aka exergonic), just so happens the reduction and oxidation that's happening respectively is what is needed to create a proton-motive force...I think
  33. Thermogenin = uncoupling protein1 (UCP1)
    • channel that allows protons to go back into matrix; not coupled and not exergonic; but energy 'lost' doesn't vanish, it's released as HEAT!
    • -found in brown fat mitochondria
    • -especially in small rodents