Energetics and enzymes

Question 1

what is an enzyme?

Answer 1

A protein that acts as a catalyst to induce chemical changes in other substances, itself remaining apparently unchanged by the process.

Question 2

how do enzymes work?

Answer 2

• substrate binds to the enzyme active site - enzyme arranges the substrates in a way that the bonds are strained - this might be in the form of oxidation reactions or reduction reactions

Question 3

what are the laws of thermodynamics ?

Answer 3

• first law : energy can neither be created or destroyed only converted from one form to another - second law: in any isolated system the degree of disorder can only increase , entropy increases

Question 4

what is gibbs free energy? what do changes in gibbs measure?

Answer 4

the amount of energy within a molecule that could perform useful work at a constant temperature. (measured in kj/mole changes in gibbs measures the amount of disorder that results from a reaction

Question 5

when does the reaction happen (negative or positive)

Answer 5

the reaction will only happy when gibbs is negative

Question 6

What are the benefits of coupled reactions?

Answer 6

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 7

is the combustion of glucose favourable or not?

Answer 7

• the combustion of glucose is energetically favourable due to the negative delta - however glucose does not spontaneously combust because it has activation energy - activation energy must be supplied before a reaction can take place

Question 8

what do enzymes do?

Answer 8

• enzymes reduce the amount of activation energy required - enzymes bend the substrates in such a way that the bonds to be broken are stressed ad the substrate molecule resembles transition state

Question 9

what is a transition state?

Answer 9

particular conformation of the substrate in which the atoms of the molecule are rearranged both geometrically and electronically so the reaction can proceed.

Question 10

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

Answer 10

• Tears and nasal secretions. - Catalyses the hydrolysis of the bond between the repeating disaccharide NAG (N-acetylglucosamine) and NAM (N-acetyl muramic acid) in the bacterial cell wall necessary for its structure therefore making it lyse. - lysozyme cleaves at the B(1-4) glycosidic linkage connecting C1 carbon of NAM to C4 carbon of NAG

Question 11

State the two essential residues in lysozyme.

Answer 11

Glu-35 and Asp-52

Question 12

Describe the mechanism of action of lysozyme.

Answer 12

• Glu- 35 protonates the oxygen in the glycosidic linkage between 2 sugars thus breaking the glycosidic bond - A water molecule enters and is deprotonated by Glu-35. - Asp-52 stabilises the positive charge in the transition state. - Hydroxide ion attacks the remaining sugar molecule adding an OH group to it - Proton is transferred to Glu-35 to return it to its original state - Glu-35 and Asp-52 are both in their original state to continue catalysis

Question 13

What is the optimum pH of lysozyme and why?

Answer 13

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

Question 14

What type of reaction is NAD+ regularly involved in?

Answer 14

Dehydrogenation – it is able to readily accept one hydrogen and two electrons it is a coenzyme it has no catalytic properties alone only functions after binding to an enzyme

Question 15

Describe the action of NAD+ in Lactate Dehydrogenase.

Answer 15

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