Enzymes

Question 1

What is the mechanism of action of an enzyme and substrate?

Answer 1

Lowers activation energy (helps substrate reach transition state)
Substrate enters active site and forms weak bonds
Enzyme and substrate form complex that prepares the substrate (intermediate state -highest energy state)
Intermediate state transforms into the product, is released and the enzyme reverts back to its original form

Question 2

What are allosteric enzymes?

Answer 2

Enzymes that act co-operatively
Binding of a substrate at one active site causes a conformational change that affects the binding of another substate at another active site

Question 3

What is the Vmax?

What is the Km?

Answer 3

Maximum velocity of a reaction (when all active sites are saturated with substrate)

Substrate concentration that gives half the Vmax

Question 4

What is the michaelis-menten model?

Answer 4

Square parabola for V(0) against [S]

With the equation: V(0) = (Vmax * [S]) / (Km + [S])

Question 5

What is the lineweaver-burn plot?

Answer 5

The Michaelis-menten model rearranged to give a linear plot
Reciprocal of V(0) against reciprocal of [S]
Closer the line is to the origin the greater the values for Vmax and Km

Question 6

What is 1 Unit of an enzyme?

Answer 6

Amount of enzyme that catalysed 1 micro-mol of Product per minute

Question 7

Why do not all enzymes obey michaelis-menten model?

Answer 7

Don’t all have to form intermediate complex before the substrate becomes the product

Question 8

What is the activity of an enzyme?

Answer 8

Rate of reaction of an enzyme
Unit per (Litre or gram) ==> micromol/minL
Directly proportional to [Substrate] and [Enzyme]

Question 9

What are the types of enzyme inhibitors and how do they affect Vmax and Km?

Answer 9

Irreversible: Binds with covalent bonds or with slow dissociation
Reversible: Bind non-covalently, can dissociate
Competitive - Increases Km
Non-competitive - Decreases Vmax