Making Unfavourable Reactions Go

Question 1

What is a favourable and unfavourable reaction?

Answer 1

A favourable reaction is one where the the actual free energy change for the reaction is negative and consequently spontaneous.

An unfavourable reaction is one where the actual free energy change is positive and non-spontaneous.

Question 2

How do you make unfavourable reactions to?

Answer 2

• Keep the concentration of products lower than the reaction
• Keep the concentration of one or more of the reactants very high
• Couple the unfavourable reaction with a more favourable reaction in the active site of an enzyme

Question 3

What is the structure of ATP?

Answer 3

ATP is a nucleotide which consists of a phosphate group, a sugar group and a base:

Phosphate group- three phosphate groups linked 5’ to ribose
Sugar - ribose
Base - adenine - linked to the 1 carbon on the ribose

Nucleoside: base + sugar

Question 4

What is Coenzyme A?

Answer 4

(thioester) X-CoA + H2O -> X + CoA-SH (thiol)

CoA functions in acyl transfer reactions where X is an acetyl, acetoacetyl or other group which is transferred to another molecule

Acetyl-CoA is central to metabolism, used in Krebs cycle, fatty aid synthesis/oxidation

Acetoacetyl-CoA is used in the switch to ketone bodies during starvation

Question 5

Give an explanation of NAD+ and NADH

Answer 5

NAD+ is the oxidised form - oxidation involves the loss of electrons, loss of hydrogen or gain of oxygen

NADH is the reduced form - reduction involves the gain of electrons, gain of hydrogen or loss of oxygen

NADP+ and NADPH are phosphorylates forms

Question 6

Explain FAD and FADH2

Answer 6

FAD is the oxidised form and FADH2 is the fully reduced form