Nature and Properties of Enzymes

Question 1

All enzymes are proteins, with the exception of ……….

Answer 1

a small group of catalytic RNA molecules

Question 2

What is a Cofactor

Answer 2

an additional chemical component needed by some enzymes for activity. It could be either one or more inorganic compounds or a coenzyme.

Question 3

What is a coenzyme?

Answer 3

a complex organic or metallorganic molecule that some enzymes need to function.

Question 4

What are prosthetic groups?

Answer 4

coenzymes or metal ions that are tightly or even covalently bound to the enzyme protein.

Question 5

……….. is a complex, catalytically active enzyme + its bound coenzyme and/or metal ions

Answer 5

Holoenzyme

Question 6

……… is the protein part of a holoenzyme

Answer 6

Apoenzyme or apoprotein

Question 7

…….. is the ability of enzymes to differentiate between structurally similar substrates. Enzyme specificity is divided into two: Optical specificity and group specificity

Answer 7

Enzyme specificity

Question 8

…………… is the portion on the enzyme molecules in direct contact with the substrate(s) during the transformation of the substrate(s) to products

Answer 8

Enzyme active site

Question 9

An account on enzyme nomenclature and classification

Answer 9

Class one, Oxidoreductases: Catalyse oxidation-reduction reactions. E.g. dehydrogenases

Class Two, Transferases: Catalyse reactions involving transfer of a group from a donor to an acceptor e.g. amino transferase

Class Three, Hydrolases: Catalyze hydrolytic reactions e.g. the cleavage of C-O, C-N, and some other bonds

Class Four, Lyases: They catalyze reactions involving the removal of a group leaving a double bond or the addition of a group to a double bond. E.g. aldolases, dehydratases, etc.

Class Five, Isomerases: Catalyze reactions involving conversion of one isomer or compound to another. E.g. epimerases

Class Six, Ligases or Synthethases: Catalyze reactions where there is a joining together of two molecules + breakdown of the pyrophosphate bond of ATP or any similar triophosphate.

Question 10

Describe the enzymatic code that was developed by IUC

Answer 10

First digit: represents the class
2nd digit: represents the sub class based on a characteristic of the enzyme
3rd digit: represents the sub sub class based on another characteristic of the enzyme
4th digit: represents the number assigned to the enzyme by EC

Question 11

Enzyme with E.C. number: 1.1.1.1. is called ……….

Answer 11

Ethanol NAD+ 1- Oxidoreductase. E.C. 1.1.1.1.

Question 12

What is enzyme kinetics

Answer 12

The study of the rate of enzyme catalyzed reaction in relation to changes in experimental parameters as a means to suggest the mechanism of each enzyme-catalyzed reaction.

Question 13

Mention some factors affection enzyme-catalysed reactions

Answer 13

pH of the medium,
temperature,
enzyme concentrations.

Question 14

……… is an energy barrier that must be surmounted before a reaction can proceed.

Answer 14

Activation energy

Question 15

How do enzymes lower activation energy?

Answer 15

by binding the transition state intermediate tightly and the binding energy of this interaction effectively reduces activation energy and increases the reaction rate

Question 16

………. is a surface that complements/best suited for the transition state in stereochemistry, position and charge.

Answer 16

Transition state intermediate

Question 17

……… determines the ability of a chemical reaction to go to completion

Answer 17

Standard free energy change ΔG0

Question 18

Represent standard free energy change mathematically

Answer 18

ΔG0 = - RT ln Keq

Question 19

The binding of an enzyme to the transition state is endergonic. True or false

Answer 19

False. The binding of an enzyme to the transition state is exergonic

Question 20

How does the binding of two or more reactants (substrates) to the enzyme’s surface, affect a reaction?

Answer 20

Proximity of the substrates on the enzyme’s surface, greatly increases the probability of productive collision between reactants

Question 21

What’s the effect of enzymes on equilibrium position?

Answer 21

Enzymes do not alter the position of equilibrium; they only affect the rate at which the equilibrium can be obtained

Question 22

What is the state of the enzymes at the end of the reaction?

Answer 22

They remain unchanged at the end of the reaction

Question 23

How does the pH of the medium affect enzyme catalysed reactions?

Answer 23

by changing the native conformation (protein structure) of the enzymes

by changing the ionic state of the substrate. Thus leading to increase or decrease in affinity of their binding to enzymes.

Question 24

Define optimum pH

Answer 24

pH at which there’s the highest percentage of residual activity i.e. pH at which the enzyme works best. Usually it’s between 5.0 and 9.0

Question 25

………….. affects the magnitude and position of the equilibrium constant

Answer 25

Increase in temperature

Question 26

State two assumptions made by Michealis and Menten to derive the relationship between velocity of the reaction and substrate concentration

Answer 26

The reaction goes through an enzyme- substrate complex intermediate

Rate of formation of the product is determined by the rate at which the E-S complex is broken down to a free enzyme and a product i.e. concentration of the E-S complex determines rate at which products are formed

Question 27

In 1925, ………….. discovered that the assumption K1»K2

Answer 27

Briggs and Haldane

Question 28

What’s the effect of activators on enzyme catalysed reactions?

Answer 28

They act by binding the enzyme into a catalytically active and stable state without, sometimes, themselves becoming involved in the reaction.

Question 29

…….. Inhibitor binds covalently to the active site

Answer 29

Irreversible inhibitor

Question 30

How do reversible inhibitors work?

Answer 30

Involves non-covalent bonding of the inhibitor with the enzyme at the active site or at any other place on the enzyme molecule

Question 31

Mention physical means through which reversible inhibitors can be removed

Answer 31

dilution or dialysis,
increasing substrate concentration

Question 32

Describe the classes of reversible inhibitors

Answer 32

Competitive inhibitors
- Inhibitor competes with substrate for the enzyme active site
- Always substrate analogues
- Vmax isn’t affected but Km is.
- Includes product and substrate inhibition

Non competitive inhibitors
- Dead-end complexes are formed
- Inhibitor binds to a site on the enzyme molecule different from the site that is meant for the substrate, or even binds to the ES complex, forming a dead- end.
- Not removed by increasing substrate concentration.

Uncompetitive inhibition
- Involves binding of inhibitor to enzyme- substrate [ES] complex only
- Alters the Vmax AND the Km
- Not removed by increasing substrate concentration

Question 33

What is turn over number?

Answer 33

Turnover number refers to the number of moles of substrate converted to product per active site of the enzyme per second, when the enzyme is fully saturated.

Question 34

……… is a substrate concentration at half the maximum velocity of an enzyme catalyzed reaction.

Answer 34

Km

Question 35

Double Displacement Mechanism (Ping- Pong)

Answer 35

-There is a release of one or more products before all the substrates are bound to the enzyme active site.

• The enzyme interconverts between two stable form

Question 36

Describe the sequential mechanism

Answer 36

• All the substrates bind to the enzyme active si te before products are formed
• Involves only one stable enzyme form which is the free enzyme

Question 37

Describe the two classes of sequential mechanism

Answer 37

Sequential mechanism is further classified into two:
- Ordered sequential Mechanism: The substrate binds to the enzyme active site and the product leaves/ dissolves from the enzyme substrate in a compulsory ordered manner
- Random order sequential mechanism: Any substrate can bind first to the active site and any product can leave first.

Question 38

What are the types of kinetic mechanism?

Answer 38

• Sequential Mechanism
• Double Displacement Mechanism/ Ping- Pong