Biology For Class IX - Chapter No.6 - ENZYMES - Questions and Answers

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CHAPTER 6
ENZYMES

By Mrs. Ayesha Arif
(Jauhar Progressive School)

Q.1: Define metabolic reactions and metabolism?
Ans: METABOLIC REACTIONS AND METABOLISM:
Life is another name of activity, therefore thousands of chemical reactions take place in the body of an organism. These reactions of an organism are collectively called metabolic reactions and This phenomenon of chemical activity called metabolism.

Q.2: A: Briefly describe the types of metabolic activities?
Ans: TYPES OF METABOLIC ACTIVITIES:
The metabolic activities are always of two types:

1. Anabolism or Constructive Reaction
2. Catabolism or Destructive Reaction

Anabolism or Constructive Reaction:
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.

Catabolism or Destructive Reaction:
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.

Q.3: What is activation energy? Or Define activation energy?
Ans: ACTIVATION ENERGY:
Definition:
The minimum amount of energy require to activate a reaction called activation energy.

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.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.

Explanation:
The chemical reaction requires particular conditions to carry down at proper rate, especially temperature and pressure. The conditions of temperature and pressure inside cell or organism are generally found not suitable for chemical reactions e.g. inside human body normal temperature remain 37 °C and pressure is 120/80 mm of Hg. These conditions of temperature and pressure are not enough to perform any chemical reactions. The activation energy needed to perform such biochemical or metabolic reactions without altering these conditions.

Q.4: What are 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 biocatalyst 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.

Q.5: Describe characteristics of enzymes.
Ans: 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.

Q.6: Define: (i) Substrate (ii) Active site (iii) Activator
Ans: (i) SUBSTRATE:
Reactants of enzymes are called substrate.

(ii) ACTIVE SITE:
A small portion of enzymes, where substrate attaches with enzymes is called active site.

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

Q.7: Define cofactor?
Ans: COFACTOR:
A cofactor is a non-protein substance which may be organic or inorganic. 

• Zn⁺², Mg⁺², Mn⁺², Fe⁺², Cu⁺², K⁺¹ and Na⁺¹ are inorganic cofactors.
• NADP, NAD and FAD are organic cofactors used in enzymes.

Cofactor can be categorized into:

• Prosthetic group (if organic cofactors are tightly bound to an enzyme) and
• Coenzymes (if organic cofactors are loosely attached with an enzyme)

Q.8: What are enzymes inhibitor?
Ans: ENZYME 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.

Q.9: Define use of enzymes in industries?
Ans: USES OF ENZYMES:
Many enzymes are used commercially in industries. The most common industries are:

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

Q.10: Explain the factors affecting the activity of an enzyme?
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 protien 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. Forexample, 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.

Q.11: Describe the models explaining the mechanism of enzyme action? OR Describe mechanism of enzymes and the models to explain enzyme action?
Ans: MECHANISM OF ENZYME ACTION:

Enzyme catalyzes the reaction by attaching to substrate which ends to the product formation. Enzyme exposes its active site to attract specific substrate, makes enzyme substrate complex (ESC) after which the product is formed and enzyme is detached from it and used again for the same reaction.

Model Or Theories for Action of Enzyme:
There are two models or theories to explain enzyme action:

1. Lock and key model
2. Induced fit model

1. The lock and key model:
This theory was first postulated by Emil Fischer in 1894 shows the high specificity of enzymes.
The “Lock and Key” model tells that enzymes and substrates fit together. Each enzymes fits specifically to a certain substrate.
This theory explains that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another like a key into a lock, only the correct size and shape of the substrate (the key) would fit into active site (the key hole) of the enzyme (the lock). However, it does not explain the stabilization of the transition state that the enzyme achieve.
For example:
Lipase fits together with lipids to break them down.

2. Induced fit model:
The induced fit model suggested by Daniel Koshland in 1958. It explains that active site continuously changes it shape until the substrate bind to it. It also says that active site of enzyme is flexible (lock and key theory doesnot explain it).

Q.12: What do you know about specificity of enzyme? OR Why enzymes are specific in nature?
Ans: SPECIFICITY OF ENZYME:
In the human body there are more than 1000 known enzymes and all work with their own substrates. These substrate are reactants used in reaction and are responsible for enzymes specificity.
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 catalyzes 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.

Q.13: Briefly describe the categories of enzymes?
Ans: Categories Of Enzymes:
There are TWO categories of enzymes:

1. Intracellular and
2. Extracellular.

1. Intracellular: enzymes work inside the cell such as ATPase, cytochrome C reductase etc.
2. Extracellular enzymes work outside the cells such as pepsin, lipase etc.

Source: Special Thanks To Sir Syed Arif Ali

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Enzymes