Energetics and enzymes

Question 1

What is the first law of thermodynamics?

Answer 1

Energy cannot be created or destroyed, only transfered

Question 2

What is the second law of thermodynamics?

Answer 2

In an isolated system, entropy can only increase.

Question 3

What is free energy?

Answer 3

Amount of energy within a molecule that could perform useful work at a constant temperature

Question 4

How can we use changes in free energy to predict the outcome of a reaction?

Answer 4

If overall amount of energy in molecules are lost after a reaction, the reaction can occur
A reaction can only occur if ΔG is negative

Question 5

How does ATP act as a free energy carrier?

Answer 5

Anabolic reactions cannot occur by themselves
Phosphoanhydride bonds have large -ve ΔG ∴ high energy release
Provides activation energy for the reaction to occur

Question 6

What is activation energy?

Answer 6

Investment of energy needed to change substrate to a transition state

Question 7

How do enzymes act as catalysts of reactions?

Answer 7

Enzymes increase rate of reaction
Lowers the activation energy
Doesn’t change ΔG or the equilibrium position of a reaction
Substrate binds to active site and enters transition state

Question 8

Define coenzyme

Answer 8

Non protein compound that is necessary for the functioning of an enzyme

Question 9

Explain the role of NAD in reactions catalysed by dehydrogenases

Answer 9

Accepts H+ and 2 e- to catalyse dehydrogenation

Question 10

How can enzyme activity be measured using spectrophotometry?

Answer 10

Use substrate which has an absorbance that can be analysed
Concentration of solution can be calculated using Beer-Lambert law
Rate can then be determined by measuring absorbance and calculating concentration at specific time intervals

Question 11

How can Km and Vmax be derived from experimental values of reaction velocity at different substrate concentrations?

Answer 11

Analysed using Lineweaver-Burk plot
Vo= Vmax x {[S]}/{[S] + Km}
Where Vo is initial rate of reaction and [S] represents substrate concentration

Question 12

What are the effects of competitive inhibitors on Km and Vmax?

Answer 12

Bigger Km

Same Vmax

Question 13

What are the effects of non-competitive inhibitors on Km and Vmax?

Answer 13

Smaller Vmax

Same Km

Question 14

What is Km?

Answer 14

Michealis constant

substrate concentration at which rate of reaction is exactly half of Vmax

Question 15

What is Vmax?

Answer 15

Maximum enzyme velocity

Question 16

What is a Lineweaver-Burk plot?

Answer 16

1/[S] plotted against 1/Vo
Line extrapolated, and at 1/[S]=0 (y intercept), 1/Vmax value can be determined
At 1/Vo=0 (x intercept), -1/Km value can be determined

Question 17

What is the Beer-Lambert Law?

Answer 17

Used for calculating the absorbance of solution in spectrophotometry
A=E x c x ℓ
Where A= absorbance
E=extinction coefficient
c= concentration mol/litre
ℓ=path length in cm