Lecture 7 Enzyme kinetics

Question 1

How does increasing substrate impace reaction velocity

Answer 1

Increasing substrate soncentration will increase reaction rate until Vmax is reached

Question 2

What is Vmax

Answer 2

• It is the maximum velocity at which an enzymes catalyses a reaction
• Once reaction reaches Vmax further increase in substrate concentration does not affect rate of reaction

Question 3

What happens at Vmax

Answer 3

• The enzyme becomes fully saturated
• Maximum rate of product production

Question 4

What is the equation for enzyme reactions

Answer 4

Question 5

What kind of Curve do we get if we plot initail velocity over substrate concentration

Answer 5

Hyperbolic curve

Question 6

What is K_m

Answer 6

K_M is 50% of Vmax

• The Concentration of subtrate which allows the enzyme to reach half of Its maximum velocity

Question 7

What is K₁

Answer 7

The Forward rate constant for enzyme association with substrate

Question 8

What is K_-1

Answer 8

Backwards rate constant for enzyme dissociation from subbstrate

Question 9

What is K₂

Answer 9

Froward rate constant for enzyme conversion of substrate to product

• This step is Irreversible

Question 10

Why does this reaction not go S + E —> P

Answer 10

Because the Activation energy barrier (now low) makes the enzyme substrate complex unstable so it can do forwards or backwards

Question 11

What is the Equation for Michaelis constant K_M

Answer 11

Question 12

How is KM and Vmax measured?

Answer 12

Measuring the intial reaction velocity V₀ at a known substrate concentration and then repeating at increased substrate concentration

Question 13

What is the Machaelis menten equation

Answer 13

• Describes Rate of catalysis at a function of substrate concentration

Question 14

What can the Mechaelis menten equation be turned into

Answer 14

• A straight line equation Y= mx+c
• Used to accuratley determined Vmas and Km

Question 15

What is the lineweaver Burk Plot

Answer 15

• A double reciprocal plot of the hyperbolic curve
• 1/V = Km/vMax . 1/[S] + 1/vmax
• X axis = 1/-K_M
• Y axis = 1/vmax
• Gradient = K_M/vmax

Question 16

What does a Low k_M indicate

Answer 16

• That enzyme needs ony a little substrate to work at its Half maximum velocity
• More effecient

Question 17

What does a High K_M indicate

Answer 17

• Enzyme needs alot of substrate to work at half-maximum velocity
• Less effecient

Question 18

Clinical Examples of why Km matters

Answer 18

Question 19

What is Reversible Inhibiton

Answer 19

Orthosteric inhibition

Allosteric inhibtion

Question 20

What is Reversible competative inhibition

Answer 20

inhibitor binds to the active site of enzymes and blocks substrate acess

• Orthosteric inhibition

Question 21

What is reversible non-competative inhibition

Answer 21

Inhibitor binding to a site other than a catalytic centre

inhibits enzymes by chaning its conformation

• Allosteric inhibition

Question 22

What is Irreversible non-competative inhibition

Answer 22

Usually involves formation or breakage of covalent bonds in the enzyme complex

• Cannot be reversed

Question 23

What does the linweaver Burk plot look like with a competative inhibitor

Answer 23

• K_m Varies - (x-axis changes)
• Vmax does not change (Y-intercept is the same)

Question 24

give an example of Competative inhibition in Clinic

Answer 24

Methanol poisoning

• Enzyme Alcohol dehydrogenase has a Km 20% greater for Ethanol compared to methanol
• Give patients 40% ethanol - which will increase the enzymes Km for its substrate - means more methanol will be required for enzyme to break it down and form harmful products

Question 25

What does the lineweaver burk plot look like with a **non-competative inhibitor**

Answer 25

* **Vmax varies** (y-intercept changes) * **Km remains the same** (x-intercept in same)

Question 26

How do enzymes carried out **Feed-back inhibition**

Answer 26

* Carried out by **Allosteric regulation** * Methabolic pathways include many enzmyes being formed and making a final product * This product can then bind to the allosteric site of an enzyme in the begining of a pathway * Which prevents the chain reaction from continueing * Simillary if the final product is in low levels then enzymes can continue to make products again

Question 27

Summary

Answer 27

Question 28

Do **Allosteric enzymes follow mechaelis menten kenetics**

Answer 28

No

Question 29

How does the curve of an **Allosteric enzyme** differ from **normal enzymes**

Answer 29

* **Allosteric enzyme = Sigmoid curve** Shows co-operative behaviour * **Normal enzyme = hyperbolic curve**

Question 30

How do allosteric activators and inhibitors effect binding of enzymes

Answer 30

Question 31

Give an example of **allosteric regulation**

Answer 31

Oxygen binding to Haemoglobin **Positive co-operativity**

Question 32

what factors cause the curve of oxygen-haemoglobin binding to change

Answer 32

* **H+ ions** * **CO2** * **2,3 Bisphosphoglycerate** - side product of glycolysis

Question 33

Questions to revise

Answer 33