Meeting 3 & 4

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Meeting 3 & 4
2012-02-24 03:52:23

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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:

    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

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