Enzymes - Lecture 2

Question 1

Define international unit of enzyme activity ( U/UI)

Answer 1

The amount of enzyme that catalysed the conversion of one micro mole of substrate per minute.

1 mole = 1x10^6 micromole

Question 2

What are 5 key features of enzymes ?

Answer 2

1) highly specific
2) unchanged after a reaction
3) they are proteins
4) increases rate of reaction
5) do not affect eq

Question 3

What does the Michaelis - menton equation explain ?

Answer 3

• explains how an enzyme works.
• E+ S = ES = E + P
• assumes that a specific complex is necessary in order for an enzyme to catalyse a reaction

Question 4

Define Vmax

Answer 4

• maximal rate where all enzyme active sites are saturated with substrates

Question 5

What are the units for Vmax?

Answer 5

Mol/min

Question 6

Define Km ( M)

Answer 6

Substrate concentration that gives half the maximum velocity

Question 7

How is Vmax related to affinity?

Answer 7

Inversely proportional.

The lower the km value , the greater the affinity

Question 8

How is Vmax related to enzyme concentration?

Answer 8

Proportional to each other

Question 9

On a Lineweaver Burk plot , if the x intercept becomes closer to 0 what does this indicate ?

Answer 9

km increases

Question 10

If the value on the y intercept of the Lineweaver Burk plot increases , what does this indicate ?

Answer 10

Vmax decreases

Question 11

Dhow does a competitive inhibitor affect km and Vmax?

Answer 11

• does not affect Vmax because eventually substrate conc will output inhibitor.
• km will increase .

Question 12

How does a non competitive inhibitor affects km and Vmax?

Answer 12

• Vmax decreases because the overall turnover of enzymes decreases.
• km stays the same because the non competitive inhibitor is not even binding to active site.

Question 13

Define activity

Answer 13

• another definition of rate - how much product is made per unit time.