Q/A Session 3

Question 1

Vo/Vi

Answer 1

• Initial reaction rate

- Velocity of reaction measured at time 0 at a particular substrate concentration

Question 2

Vmax

Answer 2

• Maximum velocity

- Velocity of reaction when enzyme is saturated

Question 3

Km

Answer 3

• An inverse measure of the affinity of the enzyme for substrate
• Defined as substrate concentration required for the reaction to proceed at 1/2 Vmax

Question 4

What is the Michealis constant?

Answer 4

• Km

- Measure of how well the enzyme binds to its substrate

Question 5

What does a low Km show?

Answer 5

Tight binding

Question 6

What does a high Km show?

Answer 6

Bad binding

Question 7

At low substrate concentration (enzyme is unsaturated)

• Reaction order
• Rate
• Velocity

Answer 7

• First order reaction
• Rate depends on substrate concentration
• Velocity increases linearly with increased substrate concentration

Question 8

At high substrate concentration (enzyme is saturated)

• Reaction order
• Rate
• Velocity
• Vmax

Answer 8

• Zero order reaction
• Rate is independent of substrate concentration
• No increase in velocity with increase of substrate concentration
• Vmax is reached

Question 9

What is kcat?

Answer 9

Catalytic rate constant (turn over number)

Question 10

The Lineweaver Burk Plot refers to

Answer 10

How much Substrate (moles) is converted to product (moles) per enzyme (moles) per unit time when enzyme is saturated with substrate

Question 11

Enzymes efficiency is

Answer 11

How quickly the substrate can be converted to product (kcat) RELATIVE TO how well the enzyme binds to substrate (Km)

Question 12

What’s the equation for enzyme efficieny?

Answer 12

kcat/km

Question 13

What are the two types of inhibition?

Answer 13

1. Reversible

2. Irreversible

Question 14

What are the two types of Reversible inhibition?

Answer 14

1. Competitive

2. Non-competitve

Question 15

What happens in Competitive inhibition?

Answer 15

-Inhibitor competes with the substrate for the active site on E

Question 16

(CI) Will reaction occur when inhibitor binds to active sit/

Answer 16

No. Inhibitor binding does affect S binding

Question 17

(CI) How can inhibition be overcome?

Answer 17

Increasing substrate concentation

Question 18

(CI) What happens to Vmax and Km?

Answer 18

Vmax stays the same

Km increases

Question 19

(CI) Describe the plot on LWBP

Answer 19

Km line is closer to 0, the Vmax intercept stays the same. Line comes out above Non inhibitor

Question 20

(CI) Describe the plot on MM

Answer 20

Km point decreases, reaches vmax. Line in below Non inhibitor

Question 21

What happens in PURE Non-Competitive inhibition?

Answer 21

-Inhibitors binds to other site on enzyme than the substrate (allosterically)

Question 22

(PNCI) Does inhibitor binding effect S binding

Answer 22

No it doesn’t. The enzyme cannot work when inhibitor is bound

Question 23

(PNCI) What happens to Vmax and Km?

Answer 23

Vmax decreases

Km stays the same

Question 24

(PNCI) Describe the plot on LWBP

Answer 24

Km point stays the same. The Vmax intercept increases (because it’s inverse). Line is above non-inhibitor

Question 25

(PNCI) Describe the plot on MM

Answer 25

Reaches same Km spot, Vmax is lower. Line is underneath non inhibitor

Question 26

What happens in MIXED Non-Competitive inhibition?

Answer 26

-Inhibitor binds to other side on enzyme than substrate (allosterically)

Question 27

(MNCI) Does inhibitor binding have an effect on substrate binding?

Answer 27

Yes it does. | Enzyme cannot work when inhibitor is bound

Question 28

(MNCI) What happens with Vmax and Km?

Answer 28

Vmax decreases | Km increases

Question 29

(MNCI) Describe the plot on LWBP

Answer 29

The Km intercept shifts closer towards 0 The Vmax intercept increases (inverse) Line is above the non-inhibitor

Question 30

(MNCI) Describe the plot on MM

Answer 30

Much lower for both than the non-inhibitor

Question 31

What occurs in irreversible inhibition?

Answer 31

Inhibitors bind covalently to the enzyme, irreversibly inactivating them

Question 32

Do allosteric enzymes in enzyme kinetics follow MM kinetics?

Answer 32

No

Question 33

What shape do allosteric enzymes follow?

Answer 33

Sigmoidal rather than hyperbolic

Question 34

Activators stabilise what state?

Answer 34

R state (high affinity for the molecule it binds configuration)

Question 35

In the presence of activator what degree of cooperativity do enzymes show?

Answer 35

Low, as they are already in the high affinity configuration

Question 36

What effect does low degree of enzyme cooperativity have on the curve? What way does the curve shift?

Answer 36

The curve is more hyperbolic and less sigmoidal. | The curve shifts LEFT

Question 37

Inhibitors stabilise what state?

Answer 37

T state (low affinity for molecules it binds configuration)

Question 38

In the presence of inhibitors what degree of cooperativity do enzymes show?

Answer 38

More cooperativity, because they are not in the high affinity configuration

Question 39

What effect does high degree of enzyme cooperativity have on the curve? What way does the curve shift?

Answer 39

The curve is less hyperbolic and more sigmoidal. | Curve shifts RIGHT