Enzyme Kinetics

Question 1

Describe enzymes

Answer 1

Catalysts: make reactions happen quickly
Work under mild physiological conditions
Specific for both reaction and substrate
Can be regulated

Question 2

Describe general enzyme reaction equation

Answer 2

E + S (reversible reaction sign) ES = E + P

Question 3

What does E stand for

Answer 3

Enzyme

Question 4

What does S stand for

Answer 4

Substrate

Question 5

What does P stand for

Answer 5

Product

Question 6

What is enzyme kinetics

Answer 6

Study of enzyme reactions

Question 7

Describe action of an enzyme (basic)

Answer 7

Enzyme substrate forms, is a reversible process

Product then dissociates and regenerates the enzyme

Question 8

What happens with low levels of substrate

Answer 8

Only a small fraction of enzyme molecules can bind at any time

Question 9

What happens at high substrate levels?

Answer 9

Most enzyme molecules substrate bound = saturated

Question 10

When you measure enzyme kinetics what do you tend to be measuring?

Answer 10

Appearance of product or disappearance of substrate

Question 11

Explain how you would measure enzyme activity of ß-galactose

Answer 11

ß-galactose is an enzyme that breaks down lactose to galactose and glucose
Give nitrophenylgalactose that breaks down to galactose and nitrophenolate which is yellow
Measure appearance of yellow colour over time

Question 12

What is the rate of reaction?

Answer 12

Velocity of reaction

Question 13

What does V stand for?

Answer 13

V

Question 14

What is created when substrate concentration plotted?

Answer 14

Hyperbolic curve

-goes up then levels out over time

Question 15

What is the Vmax

Answer 15

Maximum velocity a reaction can go

Question 16

What is Km

Answer 16

The substrate concentration that produces the velocity of have the Vmax (not half the Vmax!!)

Tells us generally about affinity of the enzyme for the substrate

Question 17

What is the michaelis-menten equation?

Answer 17

V = Vmax ([s]÷Km +[s])

V = velocity 
Vmax = max velocity
Km = v= sub contraction at vmax ÷ 2
S = substrate concentration

Question 18

What is k1

Answer 18

Binding rate

Question 19

What is K2

Answer 19

Dissociation rate

Question 20

What is Kcat

Answer 20

Catalytic constant (rate of production)

Question 21

How do you work out velocity?

Answer 21

V = kcat x concentration of enzyme substrate complex

Question 22

How do you mathematically describe enzyme catalysed reaction

Answer 22

Km = (k2+kcat) ÷ k1

Question 23

How do you work out Vmax

Answer 23

Vmax = Kcat [Etot]

Question 24

What is the conc ES

Answer 24

Same concentration as amount of enzyme put in

Question 25

What is Etot

Answer 25

Total enzyme concentration (how much enzyme put in)

Question 26

What is the relationship between Vmax and Etot

Answer 26

Directly proportional | E.g. 3rd less enzyme = Vmax a 3rd less

Question 27

What is a specificity constant

Answer 27

How efficiently an enzyme converts substrate to product

Question 28

Specificity constant equation | And how to tell from results if an enzymes specificity constant is good

Answer 28

Kcat/Km Good enzyme: Kcat = high Km = low Kcat/Km = high

Question 29

How to work out Kcat

Answer 29

Vmax/ Etot

Question 30

What is the lineweaver-Burke plot equation?

Answer 30

1/v = ((Km x 1)÷(Vmax x S)) + (1/Vmax)

Question 31

Which sections of line weaver - Burke plot relate to equation of straight line

Answer 31

(Equation of straight line: y = Mx + C) ``` 1/v = y Km/Vmax = m 1/s = x 1/vmax = c ```

Question 32

What does c stand for in straight line equation

Answer 32

Intercept

Question 33

How do you work out slope of line from line weaver Burke plot

Answer 33

Km/vmax

Question 34

What are the uses of enzyme inhibition?

Answer 34

Understanding how enzymes work | Producing drugs

Question 35

What are transition states

Answer 35

Help pull substrate into structure that lowers energy barrier for a reaction

Question 36

Competitive inhibition

Answer 36

- inhibitor similar to substrate so binds to enzymes active site - competitive inhibition because substrate and inhibitor compete to bind - reversible so inhibitor will dissociate after time and then substrate gets a chance to bind E + I (reversible reaction sign) EI

Question 37

How can you recognise competitive inhibition in enzyme kinetics

Answer 37

V max doesn’t change after inhibitor (if loads of substrate then inhibitor wont make much difference) There’s an apparent change in Km but no actual change

Question 38

What is the equation for Kmapp (the apparent Km)

Answer 38

Km app = Km (1 + I/Ki)

Question 39

What is Ki

Answer 39

Inhibitor constant (affinity of inhibitor to enzyme) The lower the value the best tier = more effective at lower amount

Question 40

Irreversible reaction

Answer 40

- inhibitors that react covalently with groups within enzymes that are essential to enzymes activity - irreversible E + I = EI

Question 41

How to see irreversible inhibition through enzyme kinetics

Answer 41

Vmax changes as enzymes inactivated permanently Concentration of substrate needed to reach vmax stays the same Km stays the same