Enzymes

Question 1

enzymes and equilibrium

Answer 1

enzymes do not alter the equillibrium of a chemical reaction

they alter the rate at which we attain equilibrium

Question 2

What are key features of an active site?

Answer 2

• it is a small part of the of the enzyme
• the active site is formed by amino acids from different parts of the primary sequence
• amino acids do not need to be adjacent in the polypeptide sequence until catalysing a reaction
• active sites are clefts or crevices
• complementary to the substrate
• the driver of a reaction is usually the absence of water because the more water there is the lower the concentration of substrate and enzyme causing there to be a lower reaction rate

Question 3

How do substrates bind to enzymes?

Answer 3

weak bonds anything other than covalent so that the products can be released

Question 4

What is Vmax ?

Answer 4

the maximal rate when all the active sits are saturated with a substrate

Question 5

What is 1 unit of an enzyme?

Answer 5

the amount of enzyme that produces 1micromol of product per min under standard conditions
- expressed as standardised rate

Question 6

Competive inhibitors

Answer 6

• reduces proportion of enzyme molecules bound to a substrate
• binds at active site

adding enough substrate will always overcome the effect of the inhibitor, so no effect on Vmax
-Km increases ; Vmax unaffected

Question 7

Non-competitive inhibitors

Answer 7

• binds at the allosteric site
• decreases concentration of functional enzyme

Inhibitor lowers effective concentration of free enzyme so adding more substrate will not overcome the effect

Non-competitive inhibition
Km unaffected ; Vmax decreases

Question 8

How is Km and Vmax affected when a competitive inhibitor is added

Answer 8

Vmax unaffected- adding enough substrate will always overcome the effect of the inhibitor

Km will increase because the inhibitor competes with the substrate for the active site km increase

Question 9

What is Km

Answer 9

Substrate concentration that give half maximal velocity

Question 10

What is the effect on Km and Vmax when a non competitive inhibitor is added

Answer 10

Km unaffected

Vmax decreases

Question 11

What is the Michaelis-Menten equation

Answer 11

V0 = Vmax [S]
————
Km + [S]

Question 12

Graph for line weaver- burk

Non competitive inhibitor

Answer 12

Lines meet at the x axis as km is unaffected

Question 13

Graph for line weaver burk

Competitive inhibitor

Answer 13

Lines cross on y axis as Vmax is unaffected