Energetics and enzymes

Question 1

What are the benefits of coupled reactions?

Answer 1

Pair an energetically unfavourable reaction with one that is energetically favourable and hence has an overall negative Gibbs free energy to allow the reaction to take place

Question 2

Where is lysozyme found and how does it provide defence against bacteria?

Answer 2

Tears and nasal secretions. Hydrolyses the bond between the repeating disaccharide NAG (N-acetylglucosamine) and NAM (N-acetyl muramic acid) in the bacterial cell wall making it lyse.

Question 3

State the two essential residues in lysozyme.

Answer 3

Glu-35 and Asp-52

Question 4

Describe the mechanism of action of lysozyme.

Answer 4

Glu-35 protonates the oxygen in the glycosidic bond thus breaking it.
Asp-52 stabilises the positively charged intermediate that’s formed.
Water becomes de protonated by Glu-35 which returns the Glu-35 to its original state.
The hydroxide ion then attacks the positively charged intermediate adding an OH to it.

Question 5

What is the optimum pH of lysozyme and why?

Answer 5

5.0 because at this pH Glu-35 is unionised and Asp-52 is ionised

Question 6

What type of reaction is NAD+ regularly involved in?

Answer 6

Dehydrogenation – it is able to readily accept one hydrogen and two electrons

Question 7

Describe the action of NAD+ in Lactate Dehydrogenase.

Answer 7

In anaerobic respiration, pyruvate is converted to lactate which generates lots of NAD+. The lactate travels to the liver where the NAD+ converts the lactate back to pyruvate