Bioenergetics FOCUS

State 1st and 2nd laws of thermodynamics, apply to living systems

1: law of conservation of energy—can’t be created or destroyed, only transformed

2. entropy always increasing

Interpret sign of ∆G to classify a reaction as exergonic, endergonic, or at equilibrium.

Positive: non spontaneous in forward, requires energy, endergonic

Negative: spontaneous, releases energy, exergonic

Zero: at equilibrium

Distinguish ∆G from ∆G′°, and use ∆G = ∆G′° + RT ln([products]/[reactants]) to explain

how a reaction with a positive ∆G′° can proceed in the cell

∆G : under actual conditions, such as in cell. Is used to desc spontaneity since depends on ratio of products/reactants

∆G′°: standard conditions (reactants and products 1M, pH 7)

— even though may be positive under standard conditions, does not represent actual conditions, which dep on ratio of products, reactants

What are coupled reactions

Unfavorable reaction paired with favorable through shared intermediate to make overall ∆G′° negative

Why is ATP hydrolysis exergonic?

1. charge repulsion

2. resonance stabilization

3. entropy increase

4. stabilization by hydration

Why does charge repulsion make ATP hydrolysis exergonic

@ pH 7, triphosphate has -4 charge, lots of repulsion and strain since close together

• when hydrolyze, relieve electrostatic repulsion

Why does resonance stabilization make ATP hydrolysis exergonic

Products, ADP and Pi, have more resonance stabilization than phosphoanhydride bond in ATP, so more stable

Why does stabilization by hydration make ATP hydrolysis exergonic

in ATP, water can’t bond (crowded)

• after hydrolysis, ADP and Pi interact much more favorably with water, which stabilizes products

Define phosphoryl transfer potential, why is ATP intermediate’s position beneficial?

Standard free energy of hydrolysis

• used to compare tendency to donate a P group

• the more negative the ∆G′°, the higher the potential

High potential can transfer phosphoryl groups to ADP to make ATP, while ATP can transfer phosphoryl to lower-potential acceptors

—> ATP act as carrier bw energy-yielding and energy-requiring reactions

Why does oxidation of carbon release energy

Oxidation=loss of electrons

C atoms in fuels are oxidized to CO2 and the e- are ultimately accepted by O2 (favorable transfer)

• the more reduced a carbon atom, the more e- it has to give up, more free energy released when oxidized

Why do fats yield more energy per carbon than glucose

Fats= lots of -CH2 bonds, are more reduced than glucose. Since more reduced, can give up more electrons, release more free energy when oxidized

• glucose already partially oxidized, so release less energy

What is E′°, what do the signs mean

E′°= standard reduction potential, tendency to accept electrons

• pos: accept e- (acceptor)

• negative: donate e- (donor)

How do you calculate ∆E′°

E′° acceptor (pos) - E′° donor (neg) = most positive

What are the activated carriers and what do they carry

ATP: phosphoryl groups

NADH, FADH2: electrons (catabolic)

NADPH: electrons (biosynth)

Conenzyme A: acyl groups

Explain how using a small set of activated carriers reflects the modular design and economy of metabolism

If use same carriers, can serve hundreds of reactions, while if had carrier for every reaction, would have millions

• Keeps metabolism economical, connects pathways via shared intermediates

• many carriers derived from vitamins, vitamins essential