Charging the cellular batteries

Question 1

Why is ATP a useful energy carrier?

Answer 1

• ATP and ADP+Pi has a high equilibrium constant
• [ATP] is maintained at ~3fold [ADP]
• this displaces the reaction in favour of of ADP+Pi –> ATP, so ATP is easily replenished

Question 2

Hydrolysis of ATP is thermodynamically unstable but It is kinetically stable.

What does this mean?

Answer 2

It will spontaneously hydrolyse but it will do so slowly.

• So ATP is good at storing energy

Question 3

Gibbs free energy released by ATP is less than other phosphate compounds.

What are the implications of this?

Answer 3

• more negative phosphorylated compounds can be used to couple ADP+Pi to make ATP

Question 4

What happens during glycolysis?

Answer 4

• formation of doubly-phosphorylated hexose.
  (Glucose –> Fructose-1,6-bisphosphate)
• Split into two trios sugars
  (by aldolase)
• Generating a doubly-phosphorylated triose sugar.
  (not thermodynamically favourable so electrons are transferred to NADH before begin phosphorylated)
• Substrate level phosphorylation
  (phosphates are transferred to ADP making 4 ATP)

Overall net gain:

• 2 ATP
• 2 pyruvate (C-3)
• 2 NADH

Question 5

Describe the transfer of electrons in the ETC during oxidative phosphorylation

Answer 5

• electrons bind to F-S cluster and haem within complexes
• electrons are transferred from complex to complexes using Cytochrome C (from complex III to IV) or Ubiquinone, NAD+ or FAD+
• As you go down the ETC electron carriers that are used have a more +ve reducing potential
• this is both more thermodynamically favourable and releases free energy