Enzyme Kinetics

Question 1

What does enzyme kinectics describe in mathmatical terms?

Answer 1

The rate of an enzyme reaction.

Question 2

In enzyme kinetics, what does S stand for?

Answer 2

Substrate concentration.

Question 3

In enzyme kinetics, what does Vo stand for?

Answer 3

The rate of enzyme reaction.

Question 4

What can be measured by adding a fixed amount of an enzyme to tubes of containing a range of substrate concentrations and measuring the rates of product formation / substrate depletion?

Answer 4

The rate of enzyme reaction.

Question 5

How can the rate of enzyme reaction be measured?

Answer 5

The rate of enzyme reaction can be measured by adding a fixed amount of an enzyme to tubes containing various concentrations of substrates and following the rate of product formation / substance depletion.

Question 6

At equilibrium, what proportion of the enzyme is reacting?

Answer 6

All of it!

Question 7

As time goes on and …………. product is produced, there are …………. susbstrate molecules for …………… to react with, so the ………………… of the reaction changes over time.

Answer 7

More, less, enzymes, kinetics.

Question 8

What must an enzyme-substrate complex be, in order for the reaction to work?

Answer 8

Stable.

Question 9

What does ‘rate constant’ (K) describe?

Answer 9

The likelihood of a reaction happening.

Question 10

What does the Michaelis-Menton equation show?

Vo = Vmax x [s] / Km + [s]

Answer 10

The Michaelis Menton equation shows the concentration of substrate needed to reach half of the maximum speed of the reaction.

Question 11

What does K stand for?

Answer 11

The rate constant - the likelihood of a reaction happening.

Question 12

What is this equation? What does it show?

Vo = Vmax x [s] / Km + [s]

Answer 12

This is the Michaelis-Menton equation, which shows the concentration of susbstrate needed to reach half of the maximum reaction velocity.

Question 13

True or false? The Michaelis-Menton equation can be represented by a graph.

Answer 13

True.

The graph represents the concentration of substrate (Km) required to reach half of the reaction’s maximum velocity (V max / 2).

Question 14

What equation is this? Which equation is it a rearrangement of?

1/Vo = 1/Vmax + Km/Vmax x 1/[s]

Answer 14

This is the Lineweaver-Burke equation, which is a rearrangement of the Michaelis-Menton equation.

Question 15

What does a Lineweaver-Burke graph show? Why?

Answer 15

A Lineweaver-Burke graph shows the gradient of the curve in a Michaelis-Menton graph.

It was used to calculate rates of reaction before computers, as it results in a straight line which is easier to read than a curve!

Question 16

What does the following describe?:

‘the maximum catalytic rate when substrate is not limiting. All the enzyme is in the enzyme-substrate complex. The enzyme is said to be saturated’.

Answer 16

Vmax.

Question 17

If Km is half of Vmax, what does it show? How can this be used?

Answer 17

Km shows an enzyme’s affinity for a substrate.

Substrate concentrations can be modulated to predict what is (or is not) being taken up.

Question 18

When a competitive inhibitor is added to a reaction, where would the line for the reaction with the competitive inhibitor cross the y-axis (1/v) of a Lineweaver-Burke graph, compared with the line for the reaction without the inhibitor?

What does this show about the Vmax?

Answer 18

The lines would cross the y-axis at the same point, whether the competitive inhibitor is present or not.

This means that the Vmax does not change when a competitive inhibitor is present.

Question 19

When a non-competitive inhibitor is present, where would the line for the reaction with the noncompetitive inhibitor cross the x-axis (1/v) of a Lineweaver-Burke graph, compared with the line for the reaction without the inhibitor?

What does this show about the Km?

Answer 19

The lines cross the x-axis at the same point whether the non-competitive inhibitor is present or not.

This shows that the Km does not change when a non-competitive inhibitor is present.

Question 20

When a competitive inhibitor is present, does the Vmax or the Km change?

Answer 20

The Vmax stays the same in the presence of a competitive inhibitor, the Km changes.

Question 21

When a non-competitive inhibitor is present, does the Vmax or the Km change?

Answer 21

The Km stays the same when a non-competitive inhibitor is present. The Vmax changes.

Question 22

What role does the enzyme chymotrypsin play in the digestion of proteins?

Answer 22

Chymotrypsin braks down larger peptides into smaller ones, working from the outside in.

Question 23

Where on large, hydrophobic amino acids does chymotrypsin work?

Answer 23

Chymotrypsin cleaves peptide bonds on the carboxyl (COOH) side of large, hydrophobic amino acids such as tyrosine, tryptophan, phenylalanine and methionine.

Question 24

True or false? Enzymes (e.g. chymotrypsin) can reform and repeatedly catalyse a reaction, regenrating itself until it is degraded or the reaction is inhibited.

Answer 24

True.

Question 25

What is substrate specificity?

Answer 25

An enzyme only works on a specific substrate, even at a certain bond within a molecule.