Enzymes

Question 1

What is an enzyme?

Answer 1

A protein molecule that catalyzes chemical reactions without itself being destroyed or altered

Question 2

What are enzymes involved in?

Answer 2

Almost every biochemical reaction

Question 3

Define substrate

Answer 3

A reactant in catalysed 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-enzyme component needed for the reaction (eg magneciusm)

Question 7

Define isoenzyme

Answer 7

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

Question 8

What is the activation energy?

Answer 8

Energy needed for the reaction to proceed

Question 9

How do molecules in free solution react?

Answer 9

By bumping into each other

Question 10

How do enzymes increase the rate of reaction?

Answer 10

Lower the activation energy

Question 11

Define riboenzyme

Answer 11

Catalytic RNA molecules with no protein compact

Question 12

What is a prosthetic group?

Answer 12

A non-protein group forming part of or combined with a protein.

i.e - A cofactor covalently bound to an enzyme or very tightly associated with an enzyme

Question 13

What is an apoenzyme?

Answer 13

An inactive enzyme.

Question 14

When does enzyme activation occur?

Answer 14

Upon binding of an organic or inorganic cofactor

Question 15

How do enzymes lower the activation energy?

Answer 15

Entropy reduction
Desolvation
Induced fit

Question 16

How does entropy reduction lower the activation energy?

Answer 16

Enzymes “force” the substrates to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed

Question 17

How does desolvation lower the activation energy?

Answer 17

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

Question 18

How does induced fit lower the activation energy?

Answer 18

Conformational change occur in the protein structure when the substrate binds

Question 19

Define Michaelis constant

Answer 19

The Michaelis constant (KM), defined as the concentration of substrate that is transported at half the maximal velocity (Vmax) of transport, is a measure of the affinity of the transporter for its substrate.

Question 20

Define the following in regards to Michaelis-Menton Constant:

V
V0
Vmax
[S]
Km

Answer 20

V = velocity aka rate

V0= initial reaction velocity

Vmax= maximum reaction velocity

[S] = substrate concentration

Km= the substrate concentration wen the reaction is at half the maximum velocity (Vmax)

Question 21

What does Km tell us?

Answer 21

Km - how specific the enzyme is for the substrate

• Low value - good fit
• High value - poor fir i.e. takes a lot of substrate to get to half Vmax

Question 22

What does Vmax tell us?

Answer 22

Vmax - how fast a reaction is proceeding when the enzyme is saturated with substrate

Question 23

What are factors that affect enzyme reactions?

Answer 23

Enzyme concentration
Substrate concentration
Temperature
pH
Inhibitors

Question 24

How does enzyme concentration affect enzyme reactions?

Answer 24

The higher the enzyme concentration, the more enzymes there are to form enzyme-substrate complexes, leading to an increase in enzyme activity.

This happens up to a certain point.

Enzyme activity then levels off (plateaus) as there are not enough substrate molecules to react with the extra enzymes.

Question 25

How does substrate concentration affect enzyme reactions?

Answer 25

Enzymes will work best if there is plenty of substrate. As the concentration of the substrate increases, so does the rate of enzyme activity. However, the rate of enzyme activity does not increase forever. This is because a point will be reached when the enzymes become saturated and no more substrates can fit at any one time even though there is plenty of substrate available.

Question 26

How does temperature affect enzyme reactions?

Answer 26

As the temperature rises, the number of collisions between the enzymes and substrate speed up, increasing the rate of the reaction. However it's important to remember the enzymes themselves are actually proteins and each enzyme will have an optimal temperature mph that it can work can't.

Question 27

How does pH affect enzyme reactions?

Answer 27

Deviating from the optimum pH (too high or too low) causes the enzyme’s active site to become denatured and the active site loses its important shape.

Question 28

How do inhibitors affect enzyme reactions?

Answer 28

Inhibitors are molecules that partially fit into an enzyme’s active site but are not broken down. They inhibit the reaction.As long as they are in the active site the substrate cannot enter to be broken down, thus reducing the rate of reaction. There are two types of inhibitors - competitive and non-competitive

Question 29

What are competitive inhibitors?

Answer 29

Competitive inhibitors are molecules with a similar structural shape to the normal substrate of the enzyme and so can fit into its active site. They compete with a substrate molecules for a position in the active site on the enzyme.

Question 30

What are non-competitive inhibitors?

Answer 30

This occurs when an inhibitor does not bind to the active site but does bind to a different part of the enzyme and changes the active site shape. This stops the substrate binding to the enzyme and decreases the reaction rate.

Question 31

What happens to the rate of a reaction with competitive inhibitors?

Answer 31

With some of the active sites occupied and blocked by the inhibitor the rate of reaction is reduced however if the substrate concentration is increased, the chance of the substrate binding to the enzyme is increased and the rate of the reaction can return to normal.

Question 32

What happens to Vmax and Km in competitive inhibition?

Answer 32

- Vmax unchanged - Km increases because it takes more substrate to overcome the inhibition

Question 33

What happens to Vmax and Km in non-competitive inhibition?

Answer 33

- Vmax decreased - Km remains the same

Question 34

Why is it important to measure enzymes in clinical settings?

Answer 34

- Detection of suspected disease at pre-clinical stage - Confirmation of suspected disease and assessing severity - Localisation of disease to organs - Assessing the response to therapy - Organ function assessment - Detection of inherited metabolic disease - Detection of vitamin deficiencies

Question 35

What factors can influence enzyme activity in samples?

Answer 35

- Age - Gender - Pregnancy - Race - Time of day - Genetics - Drugs - Disease process, progress and treatment e.g surgery

Question 36

When do serum concentrations usually rise?

Answer 36

Although there are some enzymes that are secreted from cells, generally serum concentrations are low and rise only when there is damage to cells and release of contents

Question 37

What can the release of enzymes trigger?

Answer 37

Hypoxia Cellular damage Physical damage Immune disorders Microbiological agents Genetic defects Nutritional disorders

Question 38

What is proportional to the amount of the enzyme present?

Answer 38

Rate of an enzyme-catalysed reaction is directly proportional to the amount of the enzyme present

Question 39

What is monitored when using enzymes in the lab?

Answer 39

Progress of conversion of the substrate to product is monitored

Question 40

What are the problems with enzyme measurement?

Answer 40

Not specific - i.e can be found in more than one tissue in the body Particular requirements - temperature, pH etc Assays must be optimised

Question 41

What is an assay?

Answer 41

An analysis done to determine the presence of a substance and the amount of that substance

Question 42

Why isn't a spontaneous reaction instaneous?

Answer 42

Because of the activation energy barrier

Question 43

What is the activation energy used for?

Answer 43

Positioning chemical groups correctly

Question 44

What is the transition state?

Answer 44

The moment that chemical bonds are formed and broken The reaction from this point could then go to products or reactants

Question 45

What type of bond occur between substrate and enzyme?

Answer 45

Non-covalent

Question 46

What is the active site complementary to?

Answer 46

The transition stage

Question 47

Which part of an enzyme reaction occurs more slowly?

Answer 47

The second part of the equation, producing E and P from the enzyme substrate complex

Question 48

Which stage of an enzyme reaction is reversible?

Answer 48

The formation of ES from E and S K1 denotes the forward reaction K-1 denotes the reverse reaction