Enzymes & Enzyme Kinetics

Question 1

What are enzymes ?

Answer 1

They are biological catalysts, which are not chemically altered in a reaction.

Question 2

What is the function of enzymes ?

Answer 2

They increase the rate of a reaction by providing a pathway of lower activation energy, to get reactants to products.

Question 3

Physiological conditions

Answer 3

Moderate temperature
Neutral pH
Low concentrations of substrate
Aqueous environment

Question 4

What are some features of enzymes ?

Answer 4

Active site
They have a very high specificity

Question 5

What is meant by rate enhancement ?

Answer 5

The factor by which a catalyst increases the rate of a reaction.

Question 6

Rate enhancement equation

Answer 6

Catalysed rate / Un-catalysed rate

Question 7

Disease

Answer 7

Enzyme deficiencies can cause disease.
e.g. PKU

Question 8

How are enzymes involved in diagnosis ?

Answer 8

The concentration/ activity of enzymes allows you to make a diagnosis.

Question 9

How are enzymes involved in drug therapy ?

Answer 9

Many drugs are enzyme inhibitors. The specific dosage is related to the inhibition mechanism.

Question 10

Function of lysozyme

Answer 10

Catalyses the cutting of polysaccharide chains

Question 11

Lysozyme action

Answer 11

Lysozyme binds to the polysaccharide chain, catalyses the cleavage of a specific covalent bond and releases the cleaved products.

Question 12

Vo

Answer 12

Initial reaction velocity
The speed at which the reaction proceeds before other factors come into play.

Question 13

What happens to the reaction velocity when substrate concentration increases ?

Answer 13

Vo increases

Question 14

How is Vo measured ?

Answer 14

By increasing the substrate conc. and measuring the accumulation go products over time.

Question 15

What does the enzyme activity depend on ?

Answer 15

How rapidly the enzyme can process the substrate

Question 16

What is Km ?

Answer 16

Michaelis-Menten constant
The substrate concentration required for half the maximum velocity.

Question 17

What are enzyme inhibitors ?

Answer 17

Chemicals that interfere with enzyme reactions.

Question 18

What are the 2 types of enzymes inhibitors ?

Answer 18

Irreversible
Reversible

Question 19

Irreversible inhibitors

Answer 19

Inactivators

Question 20

Reversible inhibitors

Answer 20

Competitive
Allosteric (Non-Competitive)

Question 21

What do irreversible inhibitors do ?

Answer 21

They react with the enzyme and form a covalent adduct with the protein.

Question 22

Competitive inhibition action

Answer 22

A competitive inhibitor can compete with the substrate for the active site of an enzyme.

Question 23

What is an analogy to describe competitive inhibitors ?

Answer 23

A key that gets through the keyhole but can’t unlock the door.

Question 24

With competitive inhibition on a Lineweaver Burke plot what is the effect of adding more competitive inhibitor.

Answer 24

X-intercept shifts closer to 0
Y-intercept stays the same

Question 25

Allosteric meaning

Answer 25

Allosteric inhibitors bind to the enzyme at the same time as the substrate but at a different site, called the allosteric site.

Question 26

Results of allosteric inhibition

Answer 26

Vmax decreases
Km often (but not always) increases

Question 27

With non-competitive inhibition on a Lineweaver Burke plot what is the effect of adding more non-competitive inhibitor.

Answer 27

X and Y intercept shift away from origin

Question 28

For competitive inhibition what happens to Vmax and Km

Answer 28

Vmax - unchanged

Km - increases

Question 29

For non-competitive inhibition what happens to Vmax and Km

Answer 29

Vmax - decreases due to reduced efficiency of reaction

Km - unchanged

Question 30

For mixed inhibition what happens to Vmax and Km

Answer 30

Vmax - decreases due to inhibition

Km - increases as substrate affinity in reduced