6.2 Enzyme Activity: Kinetics And Inhibition

Question 1

What is activation energy?

Answer 1

Minimum energy substrate must have for reaction to proceed

Question 2

What is the transition state?

Answer 2

High energy intermediate that lies between the substrate and product

Question 3

temp and concentration increases rate of reaction, how? (2) Knowing this, why do we want to keep this stable? (1)

Answer 3

Temp - increases no. Of molecules with Ea
Conc - increases chance of molecular collisions

Want to keep this constant as dont want denaturation of enzymes

Question 4

What is an enzyme?

Answer 4

Biological catalyst that increases rate of reaction by lowering Ea

I.e. Facilitate the formation of the transition state

Question 5

Name a few features of enzymes. (6)

Answer 5

1. Highly specific
2. Unchanged after a reaction
3. Do not affect reaction equilibrium, just helps it get there faster!
4. Proteins
5. May require cofactors
6. Increases rate of reaction

Question 6

What is an active site?

Answer 6

1. Small part of enzyme called a cleft, sort of complementary to substrate, formed by different parts of primary sequence
2. Where substrate binds and chemical reaction occurs

Question 7

Difference between lock and key hypothesis and induced fit.

Answer 7

Lock and key is where substrate has complementary shape to active site
Induced fit is where binding of substrate changes conformation of enzyme forming a complementary shape AFTER binding of substrate

Question 8

What steps does the substrate go through to become the product? (4)

Answer 8

S=>ES=>ES Transition State=>P

Question 9

On the product vs time graph, what is the shape of the line and why?

Answer 9

Rectangular hyper bola (i.e. Starts off steep then plataeu)

As we use substrate, conc of substrate decreases, product increases rapidly.
Then we start running out of substrate hence product production plateaus

Question 10

What is the michaelis menten equation?

Answer 10

E+S <==> ES => E+P

Question 11

What graph is drawn to get the constants Vmax and Km

Answer 11

Reaction Velocity (V0) vs Substrate Concentration (S)

Question 12

What is Vmax? How is it found?

Answer 12

1. Maximal velocity (mol/min)

I.e. Max rate when all enzymes active sites are saturated with substrate

2. Draw line just above plateau part on reaction velocity vs substrate conc graph

Question 13

What is Km and how is it found? (3)

Answer 13

1. Michaelis constant - Substrate concentration that gives half maximal velocity

I.e. Measures affinity for enzyme

2. Vmax/2 and then extrapolate

Question 14

1) low Km = high/low affinity for S?

2) high Km = high/low affinity for S?

Answer 14

1) High (as line is steep!)

2) Low (as line is not so steep!)

Question 15

What is the lineweaver burk plot?

Answer 15

Reciprocal graph

1/reaction velocity vs 1/[substrate]

Question 16

On the lineweaver burk plot, where is Km and Vmax found?

Answer 16

Where the line crosses the x axis, = -(1/Km)

Where the line crosses the y axis, = 1/Vmax

Question 17

What is an enzyme inhibitor?

Answer 17

Molecules that slow down/prevent an enzyme reaction from occurring

Question 18

What are the types of enzyme inhibitors? (2)(2)

Answer 18

Irreversible
Reversible
-competitive
-non-competitive

Question 19

How do Competitive inhibitors work, what kinetics do they affect and why?

Answer 19

Bind at active site
Affect Km (inhibitor competes with substrate for active site so affinity decreases)
Not Vmax (as adding enough substrate will overcome affect of inhibitor so max rate can still be reached)

Question 20

How do non-competitive inhibitors work, what kinetics do they affect and why?

Answer 20

Bind at another site, not active site
Affects Vmax (lowers) - as they decrease turnover rate of enzyme
Not Km - affinity not affected as active site not filled

Question 21

How can enzymes be used in clinical diagnosis?

Answer 21

1. Tissue damage
2. Increased release of enzymes into plasma
3. Testing levels of this enzyme will tell us extent of tissue damage

Question 22

Doubling the enzyme concentration has what affect on the rate?

Answer 22

Doubles the rate of reaction

Question 23

How can you regulate enzymes long term?

Answer 23

1. Change in protein synthesis

2. Change in protein degradation

Question 24

How can you regulate enzymes short term?

Answer 24

1. Change in substrate/product concentration

2. Change in enzyme conformation

Question 25

What is allosteric regulation?

Answer 25

‘Stuff’ that attaches to allosteric site (different to active site).

Can be allosteric activator (increases enzymatic activity)
Can be allosteric inhibitor (decreases enzymatic activity)