Subject/Biology 1/FIS 1074/TUTORIAL 6

KPJ Healthcare University College

Center of Global Professional & Social Development
Foundation in Science
Biology 1 FIS 1074

TUTORIAL 6 (ENZYMES):
Name: VIYASINEI A/P V.KUMARAMONEY
Matrix No: U0230150

1. Define enzyme. 1M

Enzymes are biological catalysts that speed up the rate of all biochemical
reactions

2. What is extracellular enzyme? 1M

Extracellular enzyme is enzyme leaves cell and functions outside the cell.

3. What is intracellular enzyme? 1M

Intracellular enzyme is enzyme remains in cell and functions inside the cell

4. State the properties of enzyme. 5M

 Enzyme activity can be affected by factors such as temperature, pH,

inhibitors, Substrate concentration and enzyme concentration
 Most are globular proteins and are coded for by DNA
 The activity of each enzyme is regulated
 Highly specific; each enzyme acts only on a specific substrate
 Can be used over and over again

5. Define active site. 1M

An active site is the site of attachment between the enzyme and substrate
molecule
6. Define activation energy. 1M

Activation energy is the initial investment of energy for starting a reaction

7. How do enzymes reduce the activation energy of a reaction? 3M

 Bring the reacting molecules together

 Expose the reactant molecule to altered charge environments that promote
catalyst.
 Change the shape of the substrate molecules

8. Explain on the Lock & Key Mechanism. 3M

 In order for an enzyme to function properly, it must first bind to its

substrate, the molecule on which it acts.
 The lock and key model of enzyme action proposes that the substrate fits
into the active site of the enzyme like a key into a lock.

9. Explain on the Induced Fit Mechanism. 3M

 The Induced Fit Mechanism is a modified version of the lock and key model
 Active site in enzyme molecule is not rigid
 Shape of active site is not exactly complementary to that of the substrate
 Enzymes are flexible and shapes of the active site can be modified by the
binding of the substrate

10. Explain the effect of substrate concentration on enzyme activity. 3M

 For a given quantity of enzyme, the rate of reaction increases as the

concentration of the substrate is increased.
 At first, this relationship is almost linear but later, the reaction curve
becomes hyperbolic in shape.
 Once all of the enzymes have bound, any substrate increase will have no
effect on the rate of reaction, as the available enzymes will be saturated and
working at their maximum rate.

11. Explain the effect of enzyme concentration on enzyme activity. 3M

 The rate of reaction is directly proportional to the amount of enzyme present

as long as the amount of substrate is not limiting.
 The substrate must be present at a concentration sufficient to ensure that all
of the enzyme molecules have substrate bound to their active site.
12. Define the terms below: 2M
a) Apoenzyme
Apoenzyme is enzyme without its cofactor

b) Holoenzyme
Holoenzyme is a complete catalytically active enzyme

13. Compare between various type of cofactors. 3M

 Coenzyme and Prosthetic group are non- protein organic substance while
metal ion are inorganic substances.
 Coenzyme and Metal ion can be separated from enzyme while Prosthetic
group cannot be separated from enzyme.
 Coenzyme is weakly bound to enzyme, prosthetic group is covalently
bound to enzyme while Metal ion bound to enzyme with weak ionic bonds.

15. Compare between competitive and non-competitve inhibitor. Give example. 5M

 Binding site of competitive inhibitor is active site while for non –
competitive inhibitor is allosteric site.
 Configuration of competitive inhibitor is similar to the substrate molecule
while for non-competitive inhibitor is no resemblance to the substrate
molecule
 Reversibility of competitive inhibitor is reversible while for non –
competitive inhibitor is irreversible.
 Competitive inhibitor does not change the conformation of the enzyme
while non-competitive inhibitor changes the conformation of the enzyme.
 The example for competitive inhibitor is succinate dehydrogenase is
inhibited by malate while for non-competitive inhibitor is cytochrome
oxidase is inhibited by cyanide

16. Explain all SIX (6) classifications of enzymes. Give example. 12M

I. Oxidoreductases
 Catalyst Oxidation
 lactate dehydrogenase

II. Transferases
 Transfer a functional group from one molecule to another
 Acetate kinase,
III. Hydrolases
 Hydrolysis
 Lipase

IV. Lyases
 Removal of groups of atoms without hydrolysis
 Oxalate decarboxylase

V. Isomerases
 Catalyse isomerisation changes from one isomer to another
 Glucose-phosphate isomerase

VI. Ligases
 Catalyse the reactions that joins two molecules with covalent
bonds
 Acetyl-CoA synthetase

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