Enzymes

Question 1

What is an enzyme?

Answer 1

A protein molecule which catalyses chemical reactions without being destroyed or altered.

Question 2

How do biological catalysts differ from chemical catalysts?

Answer 2

-Catalyses very high reaction rates
-Shows great reaction specifity
-Works in mild temperatures/pH conditions
-Can be regulated

Question 3

Define substrate.

Answer 3

A reactant catalysed in a chemical reaction.

Question 4

Define active site.

Answer 4

The part of the enzyme that binds the substrate to form the enzyme-substrate complex

Question 5

Define product.

Answer 5

The substance produced by the enzyme-catalysed conversion of a substrate

Question 6

Define cofactor.

Answer 6

Non-protein component needed for the reaction e.g. magnesium

Question 7

Define coenzyme.

Answer 7

Heat-stable substance that can aid enzyme reactions e.g. FAD from riboflavin

Question 8

Define isoenzyme.

Answer 8

Enzymes that catalyse the same reaction but vary in structure and other biochemical properties

Question 9

What is activation energy?

Answer 9

The amount of energy required for a reaction to take place.

Question 10

How do rnzymes increase the rate of reaction?

Answer 10

By lowering activation energy.

Question 11

How do enzymes increase the rate of reaction?

Answer 11

By lowering activation energy.

Question 12

Name the three ways enzymes can lower the activation energy.

Answer 12

Entropy reduction, desolvation, induced fit.

Question 13

How does entropy reduction take place?

Answer 13

Enzymes “force” the substrate(s) to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed

Question 14

How does desolvation take place?

Answer 14

Weak bonds between the substrate and enzyme essentially replace most or all of the H-bonds between substrate and aqueous solution.

Question 15

How does induced fit take place?

Answer 15

Conformational changes occur in the protein structure when the substrate binds.

Question 16

Write down the Michaelis-Menten equation.

Answer 16

V0=V(max) x S
—————–
Km

V0=initial reaction velocity
V(max)=maximum reaction velocity
S=substrate conc.
Km=the substrate concentration when the reaction is at ½ the maximum velocity (Vmax)

Question 17

What does a high/low Km measurement tell us?

Answer 17

How specific an enzyme is for a substrate

High-poor fit
Low- good fit

Question 19

What does V(max) tell us?

Answer 19

How fast a reaction is proceeding when the enzyme is saturated w substrate.

Higher the value, faster the reaction.

Question 20

Name five things that can effect enzyme activity.

Answer 20

-pH
-Temperature
-Inhibitors
-Enzyme conc.
-Substrate conc.

Question 21

Define competitive inhibition.

Answer 21

An inhibitor binds to the active site of an enzyme. to prevent the substrate from binding.

Question 22

In the presence of a competitive inhibitor, what is required to reach V(max)?

Answer 22

A higher substrate conc. is required to achieve the same velocity as if there was no inhibition.

Question 23

What happens to the V(max) in the presence of a competitive inhibitor?

Answer 23

Stays the same.

Question 24

What happens in non-competitive inhibition?

Answer 24

Inhibitor binds to the allosteric site changing the conformation and preventing the substrate from binding.

Question 25

What happens to V(max) in non-competitive inhibition?

Answer 25

Decreases

Question 26

What happens to Km in non-competitive inhibition?

Answer 26

Stays the same.

Question 27

Give a few reasons why we measure enzymes.

Answer 27

Detection of suspected disease at pre-clinical stage
Organ function assessment
Detection of vitamin deficiencies.

Question 28

What factors determine enzyme activities in serum/plasma?

Answer 28

-age
-gender
-pregnancy
-race
-time of day
-genetics
-drugs
-disease process, progress and treatment e.g. surgery

Question 29

When do serum enzyme concs rise?

Answer 29

If there is damage to cells and release of contents.

Question 30

List some processes which may trigger the release of enzymes from cells.

Answer 30

Cellular damage
Physical damage
Immune disorders
Genetic defects
Nutritional disorders

Question 31

Define hypoxia.

Answer 31

Loss of oxygen supply due to occlusion, or inadequate oxygenation, or loss of oxygen carrying capacity

Question 32

Are enzymes specific to certain tissues?

Answer 32

No- they can be found in many different organs and tissues.

Question 33

The rate of an enzyme-catalysed reaction is directly proportional to?

Answer 33

The amount of enzyme present.

Question 34

Name two methods of analysing enzymes.

Answer 34

Electrophoresis
Spectrophotometry

Question 35

Name some problems of taking enzyme measurments.

Answer 35

Not specific i.e. can be found in more than one tissue in the body so if conc is up, does not tell us where in the body it is coming from.
Particular requirements – temperature, pH etc.
Assays must be optimised to the conditions of the enzyme.

Question 36

Where can alkaline phosphate be found?

Answer 36

Bone, liver, kidney, intestine, placenta.

Question 37

List some of the reasons for a raised CK (creatine kinase) as a marker of skeletal muscle damage.

Answer 37

-Acute muscle injury
-Surgical operations
-Vigorous exercise
Rhabdomyolysis (breakdown of damaged skeletal muscle).
-Chronic neuromuscular disease e.g. Duchenne muscular dystrophy
-Acute myocardial infarction
-Statins
-Macro-CK

Question 38

What is a statin?

Answer 38

Any of a group of drugs that lower the amount of cholesterol and certain fats in the blood. Statins inhibit a key enzyme that helps make cholesterol.

Question 39

If levels of enzyme Thiopurine S-methyltransferase (TPMT) are low, what might this indicate?

Answer 39

Patient at risk of toxicity.

Question 40

If levels of enzyme Thiopurine S-methyltransferase (TPMT) are high, what might this indicate?

Answer 40

Patient might need a higher dose of the drug as it gets metabolised very quickly.

Question 41

Name some symptoms of Fabry disease.

Answer 41

Pain in hands and feet
Angiokeratomas (dark red spots on the skin).
Decreased sweating
Corneal opacity
GI problems
Hypertrophic cardiomyopathy
Renal failure

Question 42

What level of enzyme conc. is consistent w Fabry diease?

Answer 42

Low enzyme conc.