Biology For Class IX - Chapter No.6 - ENZYMES - Text Book Exercise

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CHAPTER 6
ENZYMES
Review Questions

By Mrs. Ayesha Arif
(Jauhar Progressive School)

1. Encircle the correct answer:
(i) All are characters of enzymes except:
(a) Enzyme speed up a biochemical reaction.
(b) Enzymes are sensitive to minor change in pH
(c) Enzyme activity enhanced by inhibitors ✔
(d) Enzyme portion where substrate attach called active site

(ii) Enzymes are:
(a) Steroid in nature
(b) Protein in nature ✔
(c) Lipid in nature
(d) Carbohydrate in nature

(iii) Metabolic reactions are:
(I) Constructive reactions
(II) Destructive reactions
(III) Inhibiting reactions
(a) I only
(b) I and II only ✔
(c) I, II and III
(d) II and III only

(iv) The point where the enzyme is most active is known as:
(a) Neutral pH
(b) Acidic pH
(c) Basic pH
(d) Optimum pH ✔

(v) Active site continuously changes it shapes until the substrate do not bind to it, is statement of:
(a) Induce fit model ✔
(b) Lock and key model
(c) Fluid mosaic model
(d) Both “a” and “b”

(vi) Select the mismatched:
(a) Proteases → Carbohydrate
(b) Lipases → Lipids
(c) Trypsin → Protein
(d) All are correctly matched ✔

(vii) Chemical reaction requires particular conditions to carry down at proper rate, especially:
(a) Temperature and Nature
(b) Nature and Pressure
(c) Nature and Structure
(d) Temperature and Pressure ✔

(viii)All are factors affecting enzyme activity except:
(a) pH
(b) Substrate concentration
(c) Organic solvent ✔
(d) Temperature

(ix) Rate of reaction will increase when temperature:
(a) Increases ✔
(b) Decreases
(c) Below 10°C
(d) Both “a” and “c”

(x) Choose the correct statement regarding lock and key model.
(a) Enzyme and substrate posses' specific complementary geometric shapes. ✔
(b) Active site of enzyme is flexible
(c) Active site continuously changes
(d) All above statements are correct.

2. Fill in the blanks:
(i) There are two types of metabolic reactions.
(ii) Enzymes catalyze chemical reaction by lowering the activation energy.
(iii) Presence of enzyme does not affect the nature or properties of products.
(iv) In constructive reaction large molecules are formed.
(v) Activity of enzymes can be enhanced by activator.
(vi) Small portion of enzyme where substrate attach with enzyme called active site.
(vii) Enzyme activity decreased by inhibitors.
(viii) As temperature increases, initially the rate of reaction will increase.
(ix) Enzyme changes in pH can cause enzymes to denature.
(x) In the human body there are more than 1000 known enzymes.

3. Define the following terms:

1. Substrate
2. Active site
3. Inhibitor
4. Activator
5. Anabolism
6. Catabolism
7. Activation energy
8. Cofactor
9. Prosthetic group
10. Coenzymes

Ans: (i) SUBSTRATE:
Reactants of enzymes are called substrate.
In other words, A substrate is a molecule acted upon by an enzyme. A substrate is loaded into the active 

site of the enzyme, or the place that allows weak bonds to be formed between the two molecules.

(ii) ACTIVE SITE:
A small portion of enzymes, where substrate attaches with enzymes is called active site. It is the site where the catalytic "action" happens. A substrate enters the active site of the enzyme. This forms the enzyme-substrate complex.

(iii) INHIBITOR:
An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen.

OR

Inhibitor is a substance which slows down or prevents a particular chemical reaction or other process. An inhibitor reduces the activity of a particular enzyme.

(iv) ACTIVATOR:
Enzyme activators are molecules that can bind with an enzyme to increase its activity.

OR

Activators are molecules that bind to enzymes and increase their activity. In some cases, when a substrate binds to one catalytic subunit of an enzyme, this can trigger an increase in the substrate affinity as well as catalytic activity in the enzyme's other subunits, and thus the substrate acts as an activator.

(v) ANABOLISM:
In constructive reactions large molecules are formed to form a structure of cell or body. These reactions are called anabolic reactions and this type of metabolism is called anabolism.

OR

Anabolism is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. Anabolism is the building-up aspect of metabolism.

(vi) CATABOLISM:
The destructive reaction in which large molecules breakdown in small molecules to produce energy or to re-utilize further or to discard called catabolic reactions. The type of this metabolic activity is called catabolism.

OR

The sequences of enzyme-catalyzed reactions by which relatively large molecules in living cells are broken down, or degraded is called catabolism. Part of the chemical energy released during catabolic processes is conserved in the form of energy-rich compounds.

(vii) ACTIVATION ENERGY:
The minimum amount of energy require to activate a reaction called activation energy (E_A).
e.g. the activation energy needed to break a glucose molecule initially requires energy of 2 ATP molecules. If this amount is high the difficult will be the reaction or vice versa.

OR

Living body requires some facilitators. These facilitators help to perform biochemical reactions at low energy. This minimum amount of energy is called activation energy (E_A).
e.g. the activation energy needed to break a glucose molecule initially requires energy of 2 ATP molecules. If this amount is high the difficult will be the reaction or vice versa.

(viii) COFACTORS:
Some enzymes require cofactor for their functioning; a cofactor is a non-protein substance which may be organic or inorganic. Inorganic cofactors are Zn⁺², Mg⁺², Mn⁺², Fe⁺², Cu⁺², K⁺¹ and Na⁺¹, the organic cofactors are NADP, NAD and FAD are used in enzymes as cofactors.

OR

A cofactor is a non-protein chemical compound that is bound to a protein and is required for the protein's biological activity. These proteins are commonly enzymes. Cofactors can be considered "helper molecules” that assist in biochemical transformations.

(ix) PROSTHETIC GROUP:
A prosthetic group is a tightly bound, specific non-polypeptide unit required for the biological function of some proteins. The prosthetic group may-be organic (such as a vitamin, sugar, or lipid) or inorganic (such as a metal ion), but is not composed of amino acids.

OR

A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being covalently linked to the apoprotein. OR we can say that Prosthetic group is a tightly bound, specific non-polypeptide unit required for the biological function of some enzymes.

(x) COENZYME:
A coenzyme is an organic non-protein compound that binds with an enzyme to catalyze a reaction. Coenzymes are often broadly called cofactors, but they are, chemically different. A coenzyme cannot function alone, but can be reused several times when paired with an enzyme.

OR

Coenzymes are small molecules. They cannot by themselves catalyze a reaction but they can help enzymes to do so. In technical terms, coenzymes are organic non protein molecules that bind with the protein molecule to form the active enzyme.

4. Distinguish between the following in tabulated form:
(i) Activator and Inhibitor
(ii) Anabolism and Catabolism
Ans: Difference Between Activator And Inhibitor

S.No.	Activator	Inhibitor
1.	Enzyme activators are molecules that can bind with an enzyme to increase its activity.	Enzyme inhibitors are molecules that combined with an enzyme to decrease its activity.
2.	They can be either proteins, peptides, lipids, small organic molecules or ions.	Two main types of inhibitors are reversible and irreversible inhibitors.
3.	Some important examples include hexokinase - I and glucokinase	Some typical examples include drugs, ribonucleic inhibitor, etc.

(ii) Difference Between Anabolism And Catabolism

S.No.	Anabolism	Catabolism
1.	It is a metabolic chemical process used to build molecules required for the energy to do different activities by the body.	It is a metabolic chemical process used for breakdown of complex molecules to simple small molecules.
2.	In this state body requires energy to keep body in anabolic state. Nutrition is the main source.	In this state body releases energy in different activities.
3.	In anabolism state, energy is converted from kinetic energy to potential energy.	In catabolism state, energy is converted from potential energy to kinetic energy.
4.	Anabolism helps in furnishing and preserving tissues and results in muscle growth.	Catabolism helps in burning fats and calories.
5.	Anabolism requires less oxygen compared to catabolism.	Catabolism uses oxygen.
6.	Anabolism is in function during rest or sleep.	Catabolism is in function during activities.
7.	The main role is construction in metabolism.	The main role is destruction in metabolism.
8.	Hormones involved in the process are adrenaline, cytokine, glucagon and cortisol.	Hormones involved in the process are estrogen, testasterone, growth
9.	Example of catabolic processes are proteins become amino acid, glycogen breaks down into glucose and triglycerides break down into fatty acid.	Examples include the formation of polypeptides from amino acid, glucose forming glycogen and fatty acid forming triglyceides.

5. Write short answers of following questions:
(i) Why enzymes are specific in nature?
Ans: Enzymes are specific in nature therefore a particular enzyme can only bind to its specific substrate and it's all due to its active site. Active site of the enzyme possesses some geometric shape and as the enzymes are made up of proteins and proteins contain different type of amino acids which carry different charges/nature like acidic, basic, hydrophilic etc hence active site is highly specific to its substrate.
Some of the enzymes catalyzes the reaction by recognizing the bond formed between the molecules, the functional group present in the molecules or the geometric shape of the molecules.
In general, the Absolute specificity - the enzyme will catalyze only one reaction.
For example:

• Proteases are the enzymes which catalyze the proteins only.
• Lipase acts on lipids only. It means the enzymes are bond specific, so lipase can act an ester bond in lipids/fats substances.

(ii) How enzyme reduces the amount of activation energy?
Ans: Enzymes can lower the activation energy of a chemical reaction in several ways.

• The enzymes lower activation energy by binding two of the substrate molecules and orient them in a correct and precise manner to encourage a reaction.
• Enzyme can also lower the activation energy by rearranging the electrons in the substrate so that there are areas that carry partial positive and partial negative charges which favor a reaction to occur.
• The enzymes may alter the shape of substrate. It can strain the bound substrate which forces it to transition state that favors a reaction and reduce the requirement of energy needed to make the reaction occur.

(iii) Why presence of enzymes does not effect on the nature and properties of end product?
Ans: The enzyme itself is not a component of the chemical reaction and is the same molecule at the beginning of the reaction as it is at the end. That is why their presence does not affect the nature or properties of end products.

OR

Ans: An enzyme does not effect on the nature and properties of end product because enzymes act as catalyst. They only effect the speed of the reaction and remain unchanged themselves.

(iv) How substrate concentrations affect enzyme activity?
Ans: It has been shown experimentally that if the amount of the enzyme is kept constant and the substrate concentration is then gradually increased, the reaction velocity will increase until it reaches a maximum after which further increase in the substrate concentration produces no significant change in the reaction rate.

OR

Ans: The concentration of substrate affects the enzyme activity in three ways:

1. Increase In Substrate Concentration:
   If enzyme molecules are available in a reaction, increase in the substrate concentration increases the rate of reaction.
   
2. Constant Enzyme concentration:
   If enzyme concentration is kept constant and the amount of substrate is increased a point is reached where any further increase in the substrate does not increase the rate of reaction any more.
   
3. Saturation:
   When the active sites of all enzymes are occupied at high substrate concentrations any more substrate molecule do not find free active sites. This state is called saturation of active sites and reaction rate does not increase.

(v) How enzymes are uses in industries?
Ans: Uses of enzymes:
Many enzymes are used commercially in industries. The most common industries are:

1. Paper industry- To get cellulose for paper making.
2. Food industry- For making bakery products and pizza.
3. Brewing industry- For conversion of sugar into alcohol.
4. Bio-detergents- Use to remove different type of stains.

6. Write detailed answers of the following questions:
(i) What are enzymes? Describes characteristics of enzymes.
Ans: ENZYMES: (En=inside, zyme = yeast)
The name was coined due to observation when yeast was introduced in fruit sap which converted it into alcohol.
Definition:
The high amount of activation energy cannot be provided by organism itself therefore they require some facilitators to reduce this activation energy. These facilitators are special molecules made up of mostly protein called enzymes. Thus the enzymes are the biocatalysts which facilitate chemical reaction by lowering activation energy.
This action of enzyme allows biological reaction to proceed rapidly at relatively low temperature and pressure tolerable by living organism.

OR

The molecules which facilitate biochemical reaction by reducing activation energy called enzymes. Enzymes are biocatalyst made up of mostly proteins and therefore are three dimensionally folded chains of amino acids with a specific shape.
This action of enzyme allows biological reaction to proceed rapidly at relatively low temperature and pressure tolerable by living organism.

CHARACTERISTICS OF ENZYMES:

1. Nature:
   Enzymes are biocatalyst, made up of mostly proteins and have three dimensionally folded chains of amino acids with a specific shape, held together by Hydrogen bonds.
   
   
2. Speed Up:
   Enzymes speed up reactions by bringing reactants together and reducing the activation energy required to start the reaction (enzymatic reaction).
   
   
3. Catalyst:
   When an enzyme starts a chemical reaction, catalyzes the reaction hence does not utilized itself which means even a single or little amount of enzyme can start a reaction and catalyze fastly. Their presence does not affect the nature or properties of end products.
   
   
4. Substrate:
   Reactants of enzyme are called substrate.
   They are very specific in their action; a single enzyme catalyzes only a single chemical reaction or a group of related reactions.
   
   
5. Active site:
   A small portion of enzyme where substrate attaches with enzyme is called active site. The shape of active site is complementary to shape of the substrate.
   
   
6. Sensitive:
   They are sensitive to even a minor change in pH, temperature and substrate concentration.
   
   
7. Co-factors:
   Some enzymes require cofactor for their functioning; a cofactor is a non-protein substance which may be organic or inorganic. Inorganic cofactors are Zn⁺², Mg⁺², Mn⁺², Fe⁺², Cu⁺², K⁺¹ and Na⁺¹, the organic cofactors are NADP, NAD and FAD are used in enzymes as cofactors.
   
   
8. Regulation of Metabolic Pathway:
   Many enzymes work in a sequential manner to produce a specific product. This pathway is called metabolic pathway.
   
   
9. Regulation of enzyme activity:
   Activity of enzymes can be enhanced by activator and can be decreased by inhibitors.
   An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen.

(ii) Describe factors affecting enzyme activity.
Ans: FACTORS AFFECTING THE ACTIVITY OF AN ENZYME:
The main factors which affecting the activity of an enzyme are as follows:
Substrate Concentration:
The enzyme is kept constant and the substrate concentration is then gradually increased, the reaction velocity will increase until it reaches a maximum after which further increase in the substrate concentration produces no significant change in the reaction rate.
Conclusion:
The enzyme molecules are saturated with substrate. The excess substrate molecules cannot react until the substrate already bound to the enzymes has reacted and been released or been released without reacting.

Temperature:
The protein nature of the enzymes makes them extremely sensitive to thermal changes. Enzyme activity occurs within a narrow range of temperatures compared to ordinary chemical reactions.
Enzymes catalyses by randomly colliding with substrate molecules, increasing temperature and increases collision which also increases the rate of reaction, forming more product. However, increasing temperature also increases the vibrations and structure of enzymes is lost i.e denature enzyme. These changes decreases the rate of enzyme action or it may seized completely.
Conclusion:
As temperature increases, initially the rate of reaction will increase, because of increased kinetic energy. However, the effect of bond breaking will become greater and greater, and the rate of reaction will begin to decrease.

pH:
Enzymes are also sensitive to pH due to their protein nature. All enzymes work at their maximum rate at narrow range of pH. The point where the enzyme is most active is known as optimum pH. For example, pepsin works at a low pH i.e. it is highly acidic, while trypsin works at a high pH i.e. it is basic. Most enzymes work at neutral pH 7.4.
Conclusion:
Small changes in pH above or below the optimum do not cause a permanent change to the enzyme, since the bonds can be reformed. However, extreme changes in pH can cause enzymes to denature and permanently lose their function.

Source: Special Thanks To Sir Syed Arif Ali

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Enzymes