Bioenergetics and Glycolysis

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Bioenergetics and Glycolysis

• Getting the E out of C

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Overall Chemical Reaction

• For all of Cellular Respiration
• C6H12O6 6 O2 ---? 6 CO2 6 H2O
• Overall free energy 687 kcal/mol or 3.8 kcal/g
• Not really that efficient
• (Stay tuned for the actual)

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Energy Transfer follows thermodynamic laws

• Gibbs helmholtz
• ?G ?H T?S
• Enthalpy
• Entropy
• Remember ?Suniverse gt 0 is a spontaneous process
• Overall if ?G lt 0 the process is spontaneous
• ?G -RTlnK
• Relates ?G to equilibrium
• ?G are additive
• State function
• Overall ?G has to be for a process to be
  spontaneous

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Le Chateliers Principle and ?G

• Remember Le Chatelier and affect on equilibrium
• If one reaction has a positive ?G, but the next
  reaction, which is in equilibrium has a negative
  ?G , the first reaction can be pulled through
• Many examples of this in glycolysis

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ATP (Adenosine Tri-Phosphate)
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Hydrolysis of ATP
ATP
------? ADP Pi 7.3 kcal
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Energy from ATP hydrolysis

• 7.3 kcal /mol (30.5 kJ/mol for you SI nuts)
• Energy from
• Separation of negative charges
• Increased entropy
• Phosphate now free2 things instead of one
• Resonance stabilization of phosphate

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Other Energy sources

• Hydrolysis of thioester
• Resonance stabilization of carboxylate
• Energy released from group transfer, not simply
  hydrolysis
• Coenzyme A (CoA) is an important thiol that forms
  thioesters

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Coenzyme A
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Redox

• Review
• Electron transfer reactions
• Energy from electron transfer
• Electrons typically transferred to a carrier
• NAD 2 e- 2H -? NADH H
• FAD 2 e- 2H -? FADH2
• Electrons transferred later for ATP generation

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NAD (Nicotinamide Adenine Dinucleotide)
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Reduction of NAD on Nicotinamide Ring
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FAD (Flavin Adenine Dinucleotide)
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Reduction of Flavin Ring on FAD
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Glycolysis

• In Cytosol
• Anaerobic
• Breakdown of glucose to two pyruvate molecules
• Glucose 2 ADP 2 Pi 2 NAD -? 2 pyruvate 2
  ATP 2 NADH 2 H
• C6H12O6 2 ADP 2 Pi 2 NAD -? 2 C3H3O3- 2
  ATP 2 NADH 2 H

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Glycolysis
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Hexokinase reaction

• Irreversible
• Kinase (phosphate transfer)
• -16.7kJ

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Hexose phosphate isomerase reaction

• Keto-aldol isomerization
• Glucose to fructose
• 1.7 kJ

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Phosphofructokinase reaction

• Same as hexokinase reaction
• -14.2kJ
• Major point of regulation
• Committed step
• Stimulated by ADP and AMP
• Inhibited by ATP and fatty acids

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Aldolase Reaction

• Reverse aldol condensation
• 23.8kJ
• Makes 2 3-Carbon molecules

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Triose phosphate isomerase

• Keto-enol isomerization (like hexose phosphate
  isomerase reaction)
• 7.5kJ
• Net is 2 glyceraldehyde 3 phosphate
• From now on each reaction times 2

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Glyceraldehyde -3-phosphate dehydrogenase

• Oxidation coupled to phosphorylation
• Makes NADH
• 6.3kJ
• (remember X 2)

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Phosphoglycerate Kinase

• Phosphate transfer
• Substrate level phosphorylation
• Driven by stabilization of carboxylate
• -18.5kJ
• Pulls previous reactions through

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Phosphoglycerate mutase

• Moves from 3 -? 2
• 2 steps
• Makes 2,3
• Removes 3
• 4.4kJ

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enolase

• Makes unstable enol intermediate
• 7.5 kJ

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Pyruvate kinase

• Last reaction.woohoo
• Substrate level phosphorylation
• Stabilization of enol -? keto
• -31.4kJ

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Net products from Glycolysis (per glucose)

• 2 pyruvate
• 2 NADH
• 2 ATP
• Total energy -61.3 kJ
• Sum of energies

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Fates of pyruvate
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Fates of Pyruvate

• Depend on organism and conditions
• Yeast
• Anaerobic
• Pyruvate decarboxylase
• Makes alcohol
• Aerobic
• Makes acetyl CoA ---? energy or fat
• Others
• Anaerobic
• LDH
• Makes lactate
• Sore muscles
• Aerobic
• Acetyl Co A ---? energy or fat

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Glycogen
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Glycogenolysis
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Glycogen breakdown

• Glycogen phosphorylase breaks down alpha 1,4
  linkages
• Makes glucose-1-phosphate
• Enzyme changes to glucose-6-phosphate and enters
  glycolysis there
• Cant break 1,6 linkages
• Debranching enzyme breaks 1,6 (when 4 sugars away
  from branch) and adds to end
• Glycogen phosphorylase takes over and breaks down
  the rest

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Other sugars

• Fructose
• Comes in at fructose-6-p and immediately
  phosphorylated
• Lipogenicafter branch to glycogenmakes acetyl
  CoA
• Lactose
• Glucose and galactose
• Galactose
• Epimerase turns into glucose-6-P and enters there

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gluconeogenesis

• Making glucose from pyruvate
• In liver
• Uses same enzymes as glycolysis except where
  nonequilibrium reactions
• Uses NADPH instead of NADH