Enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are protein catalysts for chemical reaction in biological systems. They increase the rate of chemical reactions taking place within living cells without changing themselves.

Question 2

What are simple enzymes?

Answer 2

Enzymes that are made up of only protein molecules not bound to any non proteins.

Question 3

Give an example of a simple enzyme

Answer 3

Pancreatic Ribonuclease.

Question 4

What fare holoenzymes/

Answer 4

Enzymes that are made up of protein groups and non-protein component

Question 5

The protein component of a holoenzyme is called …………while the non-protein component is called a ………

Answer 5

The protein component of a holoenzyme is called apoenzyme, while the non-protein component is called a coenzyme

Question 6

Examples of coenzymes that may participate in forming an intermediate enzyme-substrate complex include;

Answer 6

NAD, FAD, Coenzyme A

Question 7

Enzyme molecules contain a special pocket or cleft called the ………

Answer 7

Active site

Question 8

Outline the features of the active site

Answer 8

• The active site contains amino acid chains that create a three-dimensional surface complementary to the substrate.
• The active site binds the substrate, forming an enzyme-substrate (ES) complex.

Question 9

Describe the two parts of the active site

Answer 9

• Catalytic site. It is the part of the enzyme that is responsible for catalysis. It determines reaction specificity. Occasionally, catalytic site and active site are used synonomously.
• Binding site. It is the part of the enzyme that binds with substrate. It determines substrate specificity.

Question 10

…… determines substrate specificity

Answer 10

Binding site

Question 11

…….. determines reaction specificity

Answer 11

Catalytic site

Question 12

What is meant by enzyme turn over number?

Answer 12

Enzyme turn over number refers to the amount of substrate converted per unit time

Question 13

……….. is the fastest enzyme

Answer 13

Carbonic anhydrase

Question 14

Describe absolute specificity

Answer 14

this is a form of enzyme specificity, whereby one enzyme catalyzes or acts on only one substrate.
example: Urease catalyzes hydrolysis of urea but not thiourea.

Question 15

………. Is a form of enzyme specificity whereby an enzyme is specific to only one isomer even if the compound is one type of molecule

Answer 15

Stereo specificity

Question 16

Give examples of enzymes that exhibit stereo specificity

Answer 16

• glucose oxidase catalyzes the oxidation of β-D-glucose but not α-Dglucose,
• arginase catalyzes the hydrolysis of L-arginine but not D-arginine.
• Maltase catalyzes the hydrolysis of α- but not β –glycosides.

Question 17

Enzymes that are specific for a bond or linkage such as ester, peptide or glycosidic exhibit ……….. specificity

Answer 17

Bond Specificity

Question 18

Examples of enzymes that exhibit bond specificity are;

Answer 18

1. Esterases- acts on ester bonds
2. Peptidases-acts on peptide bonds
3. Glycosidases- acts on glycosidic

Question 19

……… are enzymes produced in nature in an inactive form which can be activated when they are required.

Answer 19

Zymogen (proenzyme)

Question 20

Outline some examples of zymogens

Answer 20

Pepsinogen - from gastric juice, when required Pepsinogen converts to Pepsin

Trypsinogen - This zymogen is found in the pancreatic juice, and when it is required gets converted to trypsin.
The activation is brought about by specific ions or by other enzymes that are proteolytic.

Question 21

A note on isoenzymes

Answer 21

These are enzymes having similar catalytic activity, act on the same substrate and produce the same product but originated at different site and exhibiting different physical and chemical characteristics such as electrophoretic mobilities, amino acid composition and immunological behavior.
For instance LDH (Lactate dehydrogenase) exists in five different forms each having four polypeptide chains. H = Heart and M = Muscle.
CPK (Creatine phospho kinase) exists in three different forms each having two polypeptide chains. Characteristic sub units are B = Brain and M = Muscle.

Question 22

The amount of energy needed to convert a substance from ground state to transition state is called ……..

Answer 22

Activation energy