Enzymes Lec 2

Question 1

What is a prosthetic group?

Answer 1

Non-protein group that forms part of or combined with a protein, tightly bound cofactors.

Question 2

What are cofactors?

Answer 2

Non-protein factors that are essential for enzyme activity e.g metal ions
Organic or nonorganic

Question 3

What are coenzymes?

Answer 3

Substances that enhances the action of an enzyme.

Organic (carbon containing) cofactors are derived from water soluble vitamins.

Question 4

What are co-substrates?

Answer 4

Loosely and transiently bound cofactors.

Question 5

Examples of cofactors

Answer 5

Iron, copper, zinc

Question 6

Examples of coenzymes

Answer 6

NAD+/NADH, Biotin, Coenzyme A

Question 7

Examples of prosthetic groups

Answer 7

Flavin

Question 8

Vitamin B3

Answer 8

Niacin
Forms NAD (nicotinamide adenine dinucleotide)
NAD is important for production of ATP from glucose hydrolysis in the citric acid cycle.
Deficiency - Cant synthesise enough NAD = disease pallagra.

Question 9

Vitamin B2

Answer 9

Riboflavin
Forms FAD (flavin adenine dinucleotide)
Deficiency - problems with mouth - lip and mouth sores, itchy + burning eyes, sore throat, skin disorders

Question 10

Vitamin B5

Answer 10

Pantothenic acid
Forms Coenzyme A
Contains Acyl group - involved in citric acid cycle and oxidation of fatty acids
Deficiency - vomiting, fatigue, stomach pain, irritability

Question 11

Vitamin B6

Answer 11

Pyridoxine
Addition of phosphate group to form pyridoxal phosphate
e.g. Synthesis of dopamine
Deficiency - sore glossy tongue, cracked lips, skin rashes

Question 12

Vitamin B7 and Coenzyme Biotin

Answer 12

Related to use of carbs and fats and amino acids
Deficiency in dogs
Deficiency in humans - hair thinning, brittle nails and skin rashes

Question 13

Vitamin B1

Answer 13

Thiamine
Coenzyme is thiamine pyrophosphate (TPP)
Deficiency = beriberi disease = Short of breath, feet swelling, increased HR and tingling in hands and feet
Involved in carbohydrate and fatty acid metabolism

Question 14

Velocity of reaction is (V)

Answer 14

Quantity of reactant which disappears in a given time

Question 15

Units for Activity/velocity

Answer 15

mmol/min or mol/sec

Question 16

Units for specific activity

Answer 16

mmol/min.mg per mg of enzyme

Question 17

what is katal

Answer 17

amount of enzyme which gives 1mol/sec

Question 18

First order reaction

Answer 18

One reactant
Reaction is directly proportional to the concentration of A
V=K[A]

Question 19

Second order reactions

Answer 19

Two reactants
V=K[A][B]
If you had loads of B and less of A it would behave as a first order reaction.

Question 20

How to measure reaction rate

Answer 20

Follow reaction over time
Measure [P] or [S] and t
Determine initial rate V0

Question 21

3 phases of an enzyme reaction

Answer 21

1) Pre steady state
2) Steady State
3) Substrate depletion

Question 22

Direct Assay

Answer 22

Assay has a way of detecting P or S directly due to some property of either e.g. if P is coloured then colour change will be monitored
Product might florescence or be gas
Measured continuosly

Question 23

Discontinuous Direct Assay

Answer 23

Enzyme quenching methods
Reaction stopped at set times and P or S measured
Assay to measure P or S may quench (stop the activity) of the enzyme
e.g Hardings test to measure glucose

Question 24

Coupled Assays

Answer 24

Sometimes neither P nor S can be measured
P can be consumed in another reaction
Product of that reaction can be measured. 2nd enzyme must be in excess so that rate limiting step is the one to be measured.

Question 25

Factors affecting enzyme rate (4)

Answer 25

1) Concentration of enzyme [E]
2) Concentration of substrate [S]
3) Temperature
4) pH

Question 26

Reaction rate is proportional to [E] providing that …

Answer 26

Substrate is not rate limiting

Product is not in excess

Question 27

Vmax

Answer 27

where the graph flattens off - maximum rate of an enzyme

Hyperbolic substrate graph - michaelis menten kinetics

Question 28

Michaelis and Menten

Answer 28

Specific enzymes substrate complex is a necessary intermediate in catalysis

Question 29

Steady state

Answer 29

Concentrations of the intermediates stay the same even though the [S] and [P] are changing.

Question 30

Michaelis Menten Equation

Answer 30

V0 = Vmax [S] / Km + [S]

Question 31

What is Km

Answer 31

The concentration of substrate that permits the enzyme to achieve half Vmax.

The higher the Km the higher the [S] needed to reach Vmax.
Enzyme with high Km has low affinity for substrate.

Question 32

Km varies for each enzyme with (3)

Answer 32

pH
Substrate
Ionic interactions

Question 33

What is a Lineweaver-Burk Plot

Answer 33

Plotting the double reciprocal to linearise the MM graph to make it easier to find Km and Vmax.
Axis 1/V0 and 1/[S]

Question 34

Kcat

Answer 34

Kcat = Rate of catalysis
Number of substrate molecules transformed per minute by a single enzyme molecule, when the enzyme is the rate-limiting factor.

Question 35

When does MM not apply

Answer 35

Allosteric Enzymes