Enzymes

Question 1

What are three ways in which enzymes are specific?

Answer 1

temperature - function optimally over a narrow range
pH - function optimally over a narrow range
substrate - are specific to a particular substrate

Question 2

What are the rules enzymes must follow during catalysis?

Answer 2

they will not catalyse a thermodynamically unfavourable reaction
- gibbs free energy must be less than zero (negative)

they will not alter the equilibrium of the reaction

they will remain unchanged at the end of the reaction

Question 3

What is the site of catalysis known as? What does it consist of?

Answer 3

the site of catalysis is the active site
- site where the enzyme-substrate complex forms

it consists of two domains

• binding site = substrate binding
• catalytic site = chemical transformation takes place

Question 4

What is the difference between the lock and key hypothesis and the induced fit hypothesis?

Answer 4

lock and key
- assumes that only one specific enzyme will be able to react with the substrate
= does not provide a model for every catalytic process

induced fit
- assumes the substrate induces the required orientation of groups in the active site necessary for binding and catalysis
= occurs as the substrate gets closer to the enzyme

Question 5

What are the methods by which enzymes lower activation energy?

Answer 5

enzymes position/align the substrate correctly so that it may attain the appropriate transition state

enzymes provide a surface or environment
- molecules in solution rely on collisions so the enzyme provides a stable surface to collide on/with

enzymes assist in weakening the bonds by

• causing changes in bond energy = due to interactions with the functional groups in the active site
• changing electron densities = due to interactions with the functional groups in the active site
• inducing distortion and bond strain = due to binding the substrate to the active site

Question 6

What units is enzyme activity usually measured in?

Answer 6

micromoles of substrate transformed per second/minute

Question 7

What are the factors affecting the rate of reaction?

Answer 7

enzyme concentration
- is the limiting factor when there is excess substrate

substrate concentration
- is the limiting factor when enzyme concentration is constant
= reaction occurs until all the enzymes are bound

Question 8

What is Michealis Constant (Km)?

Answer 8

concentration of the substrate that corresponds to half of the maximum rate of reaction
- gives an indication of the affinity of the enzyme for the substrate
= is inversely proportional to the affinity of the enzyme for its substrate

Question 9

What does a low/high Km mean?

Answer 9

Km - Michealis Constant

low Km - enzyme has a high affinity for its substrate
= needs little to become saturated

high Km - enzyme has low affinity for its substrate
= needs a lot to become saturated

Question 10

What is Vmax?

Answer 10

is a limiting value

- the rate of reaction when the enzyme is fully saturated by substrate

Question 11

What is the difference between the Michealis-Menten equation and the Lineweaver-Burk plot?

Answer 11

the Lineweaver-Burk plot is the reciprocal of the Michealis-Menten equation

the Michealis-Menten equation is more useful for determining data
- plot gives a straight line