4A- Cellular Bioenergetics

Question 1

What is ΔG?

Answer 1

ΔG is the change in Gibbs free energy

in cells, the ΔG for energy production from fuel oxidation must be greater than the ΔG of energy-requiring processes, such as protein synthesis and muscle contraction

it is basically the maximum amount of useful energy that can be obtained from a reaction

Question 2

What is the structure of ATP?

Answer 2

an adenosine molecule (adenine + ribose sugar) with 3 high-energy phophate bonds bound to the 5’ carbon

Question 3

Why is energy released when the phosphate groups of ATP hydrolyzed?

Answer 3

the produces of the reaction (ADP and phosphate) are more stable, with lower bond energies, than the reactants (ATP and H2O)

They are instable because the PO4 groups are very negatively charged and repel each other and strain the bonds between them.

Question 4

How is energy conserved during ATP hydrolysis for biosenthetic pathways?

Answer 4

cellular enzymes transfer the phosphate group directly to a metabolic intermediate or protein that is part of the energy-requiring process

Question 5

What is ΔG^o?

ΔG^o’?

Answer 5

It is the energy chagne for a reaction starting at 1 M substrate and produce concentrations and proceeding to equilibrium

It is the chemical bond energy of the products minus that of the reactants

ΔG^o’ is when there is standard conditions. pH=7.0, [H₂O]= 55M, 25^oC

Question 6

What is the typical ΔG^o’ of ATP hydrolysis?

Answer 6

-7.3kcal/mol

or

-30.5kJ/mol

Question 7

When the ΔG^o’ is negative, what does that tell you?

Answer 7

That energy was released in the reaction, since:

ΔGo’ = (energy of products) - (energy of reactants)

Question 8

What is the equation that relates ΔG^o and ΔG^o’?

Answer 8

ΔG^o = ΔG^o’ + RT*ln{[C]^c[D]^d}/{[A]^a[B]^b}

where

aA + bB <–> cC + dD

lowercase are the moles of the substance

Question 9

5. Recognize that ΔGo values are additive and can be coupled together to drive thermodynamically unfavorable reactions forward

Answer 9

a. The Go values are additive, in the sense that though some Go reactions will yield a (+) value, as long as the net Go value is (–) then the reaction is energetically spontaneous. The reactions in the pathway will move toward an equilibrium state in which the concentration of final products is greater than that of the initial products.
b. The net Go value tells you 3 things:
i. Whether the reaction releases energy- if a negative value, then yes
ii. The amount of energy involved- how big the Go value is
iii. And the ratio of products to substrates at equilibrium- in the equation
1. Go’= -RT ln[P]/[S]

Question 10

6. Calculate the K¬eq for any reaction given the Go and vice versa. Tell if a reaction will be spontaneous or non-spontaneous under stated conditions

Question 11

7. Given the Eo of a reaction, calculate its Go and vice versa. Calculate energetics of biological redox reactions involving NADH and FADH2