Biology class 9th

Class 9th Unit 6 ENZYMES Question And Answer

Class 9th Important Unit 6 ENZYMES Question And Answer

Short And Simple Question And Answer

Q.1. What do you mean by metabolism? Also write its importance and types?

Ans: Metabolism: “It is the set of biochemical reactions that occur in living things in order to maintain life”, The term metabolism is derived from a Greek word meaning “change”.
First time Ibn-e-Nafees gave the concept of metabolism. According to his concept “the body and its parts are always undergoing change.
Importance of metabolism: Metabolism helps organisms to grow, reproduce maintain their structures, respond to their environments.
and Types of metabolism: There are two types of metabolism:Anabolism: In this type of metabolism larger molecules are produced. Energy is used in anabolism.Catabolism: In this type of metabolism larger molecules are broken down. Energy is released in catabolism. Note: Energy is transferred in biochemical reactions (metabolism).

Q.2. Define enzymes, substrate and products?

Ans: Enzymes: “Enzymes are proteins that speed up biochemical reactions and are not changed during the reaction”. They are also called biocatalysts. They also lower the activation energy.
In 1878, German physiologist Winhelm Kuhne first used the term enzyme.
Substrate: “These are the molecules at which enzyme acts”.
Products: “Enzyme converts substrate into different molecules called products”.

Q.3. What is the importance of enzymes ir metabolism?

Ans: Enzymes are biocatalysts. They speed up and regulate metabolic pathways. Enzymes convert chemicals from one form to the other during metabolism. Almost all processes in a cell need enzymes.

Q.4. Explain classification of enzymes?

Ans: Enzymes are classified into two types on the basis of the site where they work.Intracellular enzymes: “These enzymes work inside the cells where they are formed”. For example enzymes of glycolysis are present in @ytoplasm.Extracellular enzymes: “These enzymes work in cavities outside the cells”. For example pepsin enzyme works in the stomach cavity.

Q.5. Define activation energy? Explain how enzymes lower activation energy through a diagram?

Ans: Activation energy: “It is minimum amount of energy required to start a reaction”.
Importance of activation energy:
a) It breaks chemical bonds and starts a chemical reaction.
b) It acts as a barrier to the beginning of reaction.
c) Enzymes lower such barriers by decreasing the requirement of activation energy.
d) Thus a reaction proceeds fast in presence of enzymes.
Methods of lowering the activation energy: Enzymes lower the activation
energy in many ways. They do this:
a) By changing the shape of substrate (and reduce the need of energy for this change).
b) By disturbing the charge distribution on substrates. b c) By bringing substrates in proper direction to react.

Q.6. Describe characteristics of enzymes?

Ans: Characteristics of enzymes:Chemical nature Almost all enzymes are proteins. They are made of amino acids.
(Enzymes are globular proteins which are made of long chains of amino acids. These chains fold and
form a three dimensional molecule) 2. Speed up the reaction: Enzymes increase the rates of reaction millions times than the reactionswithout enzymes. Enzymes are not consumed in the reactions.Specificity: Enzymes are very specific for a reaction and their substrates. 4. Active site: It is a small portion of enzyme molecule which is involved in catalysis. It identifies and binds substrate and then carries out reaction.Regulation of enzyme activity: Enzyme production can be increased or decreased by a cell according to needs. Enzyme activity can also be regulated by inhibitors and activators.
a) Inhibitors: These are the small molecules which decrease the rate of reaction controlled by an enzyme. For example some drugs and poisons.
b) Activators: These are inorganic ions which increase the rate of reaction controlled by an
enzyme. For example rate of reaction of salivary amylase enzyme increases in presence of
chloride ions 6. Cofactors: The non-protein molecules or ions which are essential for activity of many enzymes are called cofactors.
Types of cofactors: Cofactors have two types.
a) Inorganic cofactors: In these carbon atoms are not essential. For example metal ions. b) Organic cofactors: In these carbon atoms are essential. For example flavin and heme.
Types of organic cofactors: There are two types of organic cofactors.
i) Prosthetic groups: If organic cofactors are tightly bound to enzyme, they are called prosthetic groups.
ii) Coenzymes: If organic cofactors are loosely attached with enzyme, they are called
coenzymes. They transport chemical groups from one enzyme to another. Vitamins like
riboflavin, thiamine and folic acid are important coenzymes. 7. Metabolic pathways: Many enzymes work together in a specific order and form metabolic pathways. In this pathway, one enzyme takes the product of another enzyme as a substrate. After the reaction, the product is then passed to the next enzyme.

Q.7. Describe different uses of enzymes in industries?

Ans: Enzymes are mostly used in different industries for fast chemical reactions.
i) Food industry: Enzymes that break starch into simple sugars are used in the production of white bread, buns etc.
ii) Brewing industry: Enzymes break starch and proteins. The products are used by yeast for fermentation (to produce alcohol).
iii) Paper industry: Enzymes break starch to lower its viscosity that helps in making paper.
iv) Biological detergent: Protease enzymes are used for the removal of protein stains from clothes. Amylase enzymes are used for removal of starch stains in dish washing.
Q.8. Describe different factors affecting the rate of enzyme action?

Ans: Temperature, substrate concentration and pH are the factors that can affect the rate of
enzyme action. 1) Temperature: An increase in temperature increases the rate of enzyme action but
up to a certain limit.
Optimum temperature: It is a specific temperature at which enzyme works with
maximum rate. The optimum temperature for the many human enzymes is 37°C.
Denaturation of enzyme: At very high temperature globular structure of enzyme is lost. It is called denaturation of enzyme. After this rate of enzyme action is rapidly decreased and may be blocked completely.
(Temperature provides activation energy and kinetic energy in a reaction. So reactions are accelerated.)
2) Substrate concentration:
If enzymes are available, increase in substrate concentration increases the rate of reaction.
If enzymes are kept constant and substrates are increased, a point is reached when further increase in substrate does not increase the rate of reaction.
Saturation of active sites: It is a state when all active sites of enzymes are occupied and no free
active sites are available for substrate. pH: (-ve log of H ions concentration)
Optimum pH: It is a narrow range of pH when enzymes work with maximum rate. Enzyme activity is decreased or blocked with a small change in optimum pH.
Change in pH can affect the ionization of the amino acids at the active site.
Every enzyme has its specific optimum pll value.
Pepsin enzyme works in stomach. It is active in acidic medium (low pH).
Trypsin enzyme works in small intestine. It is active in alkaline medium (high pH).

Q.9. Describe the mechanism of enzyme action?

Ans: Mechanism of enzyme action:
When enzyme attaches with substrate, a temporary enzyme-substrate (ES) complex is formed.
Enzyme catalyzes the reaction and substrate is changed into product.
After this ES complex breaks and enzyme and product are released. E+P
E+S
ES complex
Models of mechanism of enzyme action:
1) Lock and key model: In 1894, a German chemist Emil Fischer proposed this model.
According to this model, both enzyme and substrate have specific shapes that fit exactly into one another. It explains enzyme specificity.
2) Induced-fit model: In 1958, an American biologist Daniel Koshland proposed this model.
According to this model, active site is not a rigid structure. It is molded into Fig: Induced fit model the required shape to perform its function. Induced fit model is more acceptable than “lock and key”
model.

Q.10. Write a note on specificity of enzymes?

Ans: Specificity of enzymes:
There are over 2000 known enzymes Each enzyme is involved only in one specific reaction.
They are also substrate specific.
Specificity of enzymes is determined by the shapes of their active sites.
Active sites have specific shapes that fit with specific substrates.
Example:
a) Protease enzyme breaks peptide bonds in proteins. It does not work on starch.
b) Amylase enzyme breaks starch into glucose. c) Lipase enzyme acts only on lipids. It digests them into fatty acids and glycerol.

Q.12. In a range of 0-35°C, the rate of reaction of un enzyme is proportional to temperature, Above 35°C and below 0°C, enzyme activity slows down and eventually stops. Explain why?

Ans. Above 35°C globular structure of enzyme is lost. This is known as denaturation of of enzyme. It results in a rapid decrease in rate of enzyme action and it may be blocked. Below optimum temperature (0°C) the reacting molecules move slowly so reaction slow down

Q.13. What is the difference between catalyst and biocatalyst?

Ans: Catalyst: It is a substance which speeds up chemical reaction and is not used itself during the reaction.
Biocatalyst: It is a substance which speeds up chemical reaction in a living cell and is not used itself
during the reaction.

Q.14. Is there any relationship between lock and key model and induced fit model?

Ans: Induced fit model is a modified form of lock and key model.

Q.15. All biocatalysts are protein in nature or not?

Ans: All biocatalysts are not protein in nature some RNA molecules also catalyze reactions.

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