Enzyme Actitivity

Question 1

How are enzyme active sites formed and how do they work?

Answer 1

• active site is a small part of an enzyme, (few a.a residues long)
• can come from different regions in primary sequence (rest of protein holds them together in correct orientation)
• are cleft/crevices, no water entry as water is highly concentrated
• induced fit model (not completely complementary)(non-covalent attractions between active site and substrate)

Question 2

When may reaction rate represent a rectangular parabola

Answer 2

Plot of reaction velocity against substrate concentration. Curve tends towards a max velocity

Question 3

What’s the Michaelis-Menten model for enzyme action?

Answer 3

• proposes that a specific complex between substrate and active site is an intermediate in catalysis
• E + S ES -> E + P

Question 4

What’s the Michaelis-Menten equation, what’s it for?

Answer 4

It predicts that a plot of Vo vs [s] will be a rectangular hyperbola.
NOT ALL ENZYMES WILL OBEY THIS MODEL

Vo=Vmax[s]/(Km + [s])
Here, Km is the Michaelis constant, substrate conc that gives half of max velocity (M units for conc)
Vmax is max rate when all enzyme active sites are saturated with substrate in mol/min

Question 5

How can you find the Km value of a reaction and what may this represent?

Answer 5

Km is substrate conc at half of max velocity. Use the graph and extrapolate.

Low Km=high affinity for substrate
High Km=low affinity for substrate

Question 6

1 unit of enzyme is what

Answer 6

The amount of enzyme that converts 1umol of product per min under standard conditions

(Often in a standardised rate - per L of serum/ per g of tissue

Question 7

What’s the lineweaver-burk plot?

Answer 7

Rearrangement of the Michealis-Menten equation gives… (y=mx+c)

1/Vo = (Km/Vmax)(1/[s]) + 1/Vmax

Therefore can plot 1/Vo against 1/[s]

Question 8

What are enzyme inhibitors

Answer 8

Can be irreversible (bind tightly-covalent bonds)

Can be irreversible (either competitive or non competitive)

Question 9

What effects do Competitive and non competitive inhibitors have on features of the Lineweaver-Burk Plot

Answer 9

Competitive; increases Km, no effect on Vmax

Non-competitive; no effect on Km, decreases Vmax.

(Draw graphs out to understand)