Bioenergetics

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Bioenergetics

• Intro/Chpt 14

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Catabolism energy prodn in cells
(Fig. 4, p487)

• Glycolysis
• Intermediary metabolism
• ATP production
• Mitochondrial
• Chloroplast

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Fig. 4, p.487
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Regulatory enzymes

• Rate limiting
• Modulators control /-
• Allosteric
• Covalently modified
• Combination
• Pathway commitment

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Metabolic rxns follow trends

• 50 rxns
• Only 5 major types (REMEMBER?)
• Coupling
• Redox rxns impt

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Thermodynamics (again!)

• D G D H - T D S
• D G - Exergonic heat given off
• D H - Energy released w/ bonding rxn
• D S Increased entropy (incrd randomness)
• D Go Std free energy (pH7, H2O55 M,
  reactant1 M, T25oC) physio conds in cell

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Thermodynamics (again!)

• For cellular rxn
  a A b B lt gt c C d D at equilib
• Keq can be written
• Keq related to D Go (Table 14-2)
• Can predict D Go from Keq and vice/versa (Table
  14-3)

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In real life

• Not all reactants _at_ 1 M
• Go back to D G
• D G D Go RT ln (CcDd/AaBb)
• Theoretical max energy for rxn
• Actual energy available to system lt
  theoretical

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In real life contd

• Not all thermodynamically favorable rxns proceed
  at measurable speeds
• Enzyme catalysis impt
• D G relationship to k is inverse and exponential
  (REMEMBER??)
• D G stays the same

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In sequential reactions

• If common reactants, products
• D Go values are additive
• So thermoly unfavorable rxn can be driven by
  thermoly favorable rxn coupled to it
• Keq values are multiplied
• So see large differences in Keq of coupled rxns
• Commonly coupled to endergonic rxns
• ATP hydrolysis D Go -30.5 kJ/mole
• Coupling hydrol of n ATPs raises Keq by 108n

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ATP hydrolysis adds energy

• Products of hydrolysis are resonance stabilized
  (14-1)
• Decrd electrostatic repulsions in ADP
• Pi Os can share charge

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Fig. 14-1
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ATP hydrolysis adds energy

• Mg coordinates w/ ADP (14-2)

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ATP hydrolysis adds energy

• Pi or AMP often covly couples w/ reactants
• ? High energy intermediate
• Larger D G when cleaved
• Glutamate (14-8)
• First step in glycolysis activates glucose

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Fig. 14-8
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Some notes

• ATP may bind non-covalently to protein
  hydrolysis provides energy for conforml change
• Ex Na/K ATPase
• Other phosphorylated cmpds release energy w/
  cleavage of Pi (Table 14-6)
• Products also often resonance stabilized (14-3,
  14-4)
• BUT original source of Pi is ATP ? ADP Pi

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Fig. 14-3
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Fig. 14-4
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Some (more) notes

• Thioesters impt
• Acetyl CoA example (14-6)
• Greater D G for hydrolysis (14-7)
• Nucleoside triphosphates are source of
  nucleotides incd into DNA, RNA (w/ release of
  energy) (14-12)

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Fig. 14-6
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Fig. 14-7
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Fig. 14-12
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Biological Oxidation Reduction Reactions
(Redox)

• Flow of e-s changes redox state of reactants,
  products
• Reactant that goes from more redd ? more oxd
• e-s accepted by another molecule, goes from more
  oxd ? more redd

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Redox Rxns contd

• Battery as example of e- flow ? energy
• Two linked solns w/ differences in affinities
  for e-
• Coupled through e- carrier
• Carrier associated w/ motor, which can give off
  energy (in the form of work)

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Redox Rxns contd

• Cellular analogy
• Two solns two molecules w/ differing
  affinities for e-
• e- carrier cofactor (molecule)
• Motor ATP synthesis machine in mitochondrion
  which can give off energy (in the form of a
  chemical with high potential chemical energy)

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Redox Rxns contd

• Metabolism of nutrients converts cmpds from more
  redd ? more oxd states
• By LEO/GER, nutrient loses electrons (e-s)
• e-s released to system BUT are NOT free in
  cytoplasm
• e-s transferred to carrier mols
• By LEO/GER, carrier mols now redd

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Biological Oxidation Reduction Reactions
(Redox) contd

• Redd carrier mols bring e-s to mitoch
• Electron transport system
• Coupled to oxidative phosphn
• ? ATP prodd

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Redox Rxns (contd)

• Rxns of e- flow (reductant or e- donor ?
  oxidant or e- acceptor) can be additive
• Imptc free energy of system changes w/ change
  in redn potential of reactants/products in rxn
• D E diff in redn potentials of reductant,
  oxidant
• Related to free energy of system ( D G) (eqn
  14-6)
• Use to calc D Gs for biol. oxns

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Redox Rxns (contd)

• e- flow from lower redn potential ? higher redn
  potential (Table 14-7)
• Eo additive if coupled rxns have common
  intermeds
• Use to calc D Gs for biol. oxns

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Redox Rxns (contd)

• Cells rxns (incl redox) involve organic cmpds
• Consider ownership of e- by C in a cmpd (14-13)
• Oxn C-contng cmpds often w/ bonding O to C,
  displacing H
• More redd cmpds more Hs, fewer Os
• More oxd compds more Os, fewer Hs

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Fig. 14-13
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Redox Rxns (contd)

• Oxidation may occur in 4 ways
• Electrons transfer directly
• As H e-
• As combination w/ O2
• As H- (hydride ion)
• Common mechanism w/ carriers
• Reducing equivalents

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Nicotinamides -- NAD, NADP

• When oxd NAD, when
  redd NADH
• One C on nicotinamide ring accepts e- as H-
• Hydride donor also releases one H to system
• Overall
  NAD 2e- 2H ? NADH H

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Fig. 14-15a
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NAD, NADP contd

• NADP preferred by some enzs, species
• NAD/NADH gtgt NADP/NADPH
• NAD usually gt NADH
• Commonly donates or accepts hydride?
• NADP usually lt NADPH
• Enzs oxidoreductases or dehdrogenases
• gt 200 (Table 14-8)
• Loosely assocd w/ deHases
• Move between enzymes
• Recycled by cell

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Flavin Nucleotides FMN, FAD

• Derd from riboflavin
• Isoalloxazine ring accepts 1 or 2 e-
• Semiquinone (partly redd)
• Quinone (fully redd)
• Often bound more tightly to enzs
• Prosthetic grps
• Varied enzs associate w/ flavins
• Table 14-9

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Fig. 14-16
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