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Energy and Metabolism 1
Energy and Metabolism Chapter 6
Topics you are not responsible for:How biochemical pathways evolve
Read on your own about:Laws of thermodynamics
End of Chapter questions: all
Do all mQuiz questions
Energy and Metabolism 2
How does the body “deal with” alcohol?
Too much of a bad thing Too much of a good thing
NADH -- e- source for ATP production-- too much causes metabolic
disordersADH deficiency in Asian races
Disulfiram (antabuse) – ADH inhibitor
Energy and Metabolism 3
How much “useable” energy exists in the molecules of a cell?
G = H - TS
G = usable energy (Gibbs free energy)
Which equals …
H = energy content in the molecular bonds (enthalpy)?
… Less …
S = disorder (entropy)
x Temperature (Kelvin scale)
Energy and Metabolism 4
What happens to the energy of a molecule during a chemical reaction?
How does the energy content in the molecular bonds (enthalpy) change?
ΔH
How does the energy of disorder (entropy) change?
ΔS (x Temperature)
How does the total usable (‘Free’) energy (G) of the system change during the reaction?
ΔG = ΔH – ΔST = -7 Kcal/mol
“Catabolic” reaction “Exergonic” -- energy is released
Energy and Metabolism 5
Catabolic (exergonic) reactions occur spontaneously… but often slowly. Why?
What is activation energy?
Energy and Metabolism 6
What happens if the reaction is reversed?
Will ΔG (usable energy of the system) be increase or decrease?
What happens to useable energy of the system?
ΔG = ΔH – ΔST = +7 Kcal/mol
Example of an Anabolic reaction (endergonic) -- energy must be added to the system
Energy and Metabolism 7
How does an enzyme affect reaction energetics?
How does it do so?
“Catalytic site”
Substrate orientation
Enzyme movements
Bond destabilization
Catalysis
Funke T et al. PNAS 2006;103:13010-13015
EPSP synthase binding to SP3
Energy and Metabolism 8
Enzyme reactions are reversible
In a closed system. . . . . . will reach “equilibrium”
-- what does this mean?
Sucrase Equilibrium Constant = 1.4x105 (140,000)= [products] = ____[G] x [F]___ [reactants] [sucrose] x [H20] If > 1, Rx is exergonic
Why aren’t [ ]s the same at equilibrium? -- affinities for catalytic site
What is EC of reverse sucrase reaction?
Energy and Metabolism 9
In enzymatic reactions, energy can pass to or from ATP
Glutamine synthase reaction Glutamate + NH3 + ATP Glutamine + ADP + Pi
if: Substrate +ATP Product + ADP +Pi = endergonic / anabolic reaction
if: Substrate +ADP+Pi Product + ATP = exogonic / catabolic reaction
Understand this
Energy and Metabolism 10
What is a metabolic pathway?
-- sequential series of enzymatic reactions-- e.g., Glycolysis, Krebs cycle, etc. Enzyme 1
Enzyme 2
Enzyme 3
Cellular “metabolism” = sum of all enzymatic activities
Energy and Metabolism 11
If all enzymes are reversible, then why do molecules pass one way through metabolic pathways?
What controls flow direction?
1) Reactant vs Product affinities
2) Reactant vs Product concentrations
2) Product removal
Fig 6.13 in text is special case
Energy and Metabolism 12
What controls the rate of enzyme activity?
Various physical factors?pH
Temperature
Reactant & substrate concentrations
Activators and Inhibitors
Models
Energy and Metabolism 13
Control of enzyme activity, con’t.
Inhibitors
competitive
vs
non-competitive
InhibitorsInhibitors
Non-competitive = “allosteric regulation”