2 Energetics And Enzymes

Question 1

Q: Define enzyme?

Answer 1

A: protein that acts as a catalyst to induce chemical changes in other substances while itself remaining unchanged

Question 2

Q: Define Gibbs free energy?

Answer 2

A: the amount of energy within a molecule that can perform useful work at a constant temperature

Question 2

Q: Do reactions spontaneously proceed towards products with lower or higher entropy?

Answer 2

A: higher

Question 3

Q: What is the unit for Gibbs free energy?

Answer 3

A: kJ/mol

Question 5

Q: How do you calculate Gibbs free energy of a reaction?

Answer 5

A: free energy of p - that of r

Question 6

Q: For a reactive to occur simultaneously, what does delta G need to be?

Answer 6

A: negative

Question 7

Q: What is a coupled reaction and why are they useful?

Answer 7

A: energetically unfavourable reaction coupled with a favourable one which results in overall negative delta G

Allows energetically unfavourable reactions to take place

Question 8

Q: Define transition state.

Answer 8

A: particular conformation of a substrate where atoms are rearranged electronically and geometrically for reaction to proceed

Question 9

Q: What do enzymes do to get substrate in transition state? How do they put strain on bonds?

Answer 9

A: oxidation reactions (electron removal) or reduction (gain)

Question 10

Q: What is lysozyme and where is it found?

Answer 10

A: first line of defence against bacteria and nasal secretions and tears

Question 11

Q: How does lysozyme catalyse reactions?

Answer 11

A: catalysed hydrolysis of sugar molecules in bacterial cell walls, causes damage and bacteria die

Copolymer of N-acetyl glucosamine NAG and N-acetyl muramic acid NAM with glycosidic bond between

Glu35 protonates oxygen and causes a break and glu35 to lose a H

Water is deprotonated by glu35 so that it gains a H and the hydroxyl group binds to remaining sugar

Asp52 stabilises the positive charge in transition state

Question 19

Q: What’s the optimum pH of lysozyme?

Answer 19

A: 5 where asp52 is ionised and glu35 is not

Question 20

Q: What does NAD stand for?

Answer 20

A: Nicotinamide adenine dinucleotide (coE)

Question 21

Q: What process produces lots of of free NAD+?

Answer 21

A: anaerobic respiration where pyruvate becomes lactate

Question 23

Q: What does NAD+ readily catalyse and accept?

Answer 23

A: dehydrogenation and a proton and 2 electrons

Question 24

Q: What is the role of lactate dehydrogenase?

Answer 24

A: conversion of lactate to pyruvate using NAD+ in liver

Question 25

Q: What does glucose 6 phosphatase do?

Answer 25

A: catalyse removal of phosphate group from glucose 6 phosphate in liver to release glucose from the glycogen stores when blood glucose is low

Question 26

Q: What is the Km of an enzyme? For practical purposes? How is it affected by competitive inhibition? how? By non competitive inhibition?

Answer 26

A: Km (Michaelis constant) of the enzyme, an inverse measure of affinity.

For practical purposes, Km is the concentration of substrate which permits the enzyme to achieve half Vmax

increase Km by interfering with the binding of the substrate

unchanged

Question 27

Q: What is Vmax of an enzyme? How does competitive inhibition affect? Non competitive?

Answer 27

A: rate of reaction when the enzyme is saturated with substrate is the maximum rate of reaction=Vmax

unchanged- inhibitors can’t bind to the ES

reduced