RBSE Solutions Class 12 Biology Chapter 9 Enzymes

Rbse Class 12 Biology Chapter 9 Multiple Choice Questions

 

Question 1. In what respect enzymes are different from catalysts?
(a) High diffusion rate
(b) Active at high temperature
(c) Protein nature
(d) Used in the reaction
Answer: (c) Protein nature
In simple words: Enzymes are special types of catalysts that are made of protein. Other catalysts can be made of different things. This protein structure makes enzymes unique.

🎯 Exam Tip: Remember that while all enzymes are catalysts, not all catalysts are enzymes. The key distinction is their protein composition and biological origin.

 

Question 2. The non-protein part of holoenzyme is called?
(a) Apoenzyme
(b) Co-factor
(c) (Option was incomplete in source)
Answer: (b) Co-factor
In simple words: A holoenzyme has two parts: a protein part called apoenzyme and a non-protein part. The non-protein part is known as a co-factor, which helps the enzyme work properly.

🎯 Exam Tip: Distinguish clearly between apoenzyme (protein part) and co-factor (non-protein part) as they combine to form a complete, active holoenzyme.

 

Question 3. Which of the following statement is absolutely correct?
(a) All proteins are enzymes
(b) All enzymes are proteins
(c) Most enzymes are proteins
(d) None of the options
Answer: (c) Most enzymes are proteins
In simple words: It is true that most enzymes are made of proteins, but not all enzymes are proteins (like ribozymes). Also, not all proteins are enzymes, as proteins have many other jobs in the body.

🎯 Exam Tip: Avoid common misconceptions; remember the exceptions like ribozymes, which are RNA enzymes, making "most enzymes are proteins" the most accurate statement.

 

Question 4. Which enzyme was discovered first of all?
(a) Zymase
(b) Lipase
(c) Pepsin
(d) Isomerase
Answer: (a) Zymase
In simple words: The first enzyme ever found and studied was called Zymase. It plays a role in fermentation, which is how yeast converts sugar into alcohol and carbon dioxide.

🎯 Exam Tip: Historical facts like the first discovered enzyme are often asked in multiple-choice questions, so remember key milestones in biology.

 

Question 5. Enzyme activity is affected by -
(a) pH only
(b) Substrate concentration
(c) only temperature
(d) All of the options
Answer: (d) All of the options
In simple words: An enzyme's activity can be changed by many things. These include the pH level, how much substrate is present, and the temperature. All these factors play a role in how well an enzyme works.

🎯 Exam Tip: When considering factors affecting enzyme activity, remember that pH, temperature, and substrate concentration are primary influences, alongside enzyme concentration and the presence of inhibitors/activators.

 

Question 6. Non-Competitive inhibitors are the substances which?
(a) Combine to the active sites of the enzyme
(b) Decrease the active sites of the enzyme
(c) Change the structural organisation of the enzyme
(d) Change in the properties of an enzyme
Answer: (c) Change the structural organisation of the enzyme
In simple words: Non-competitive inhibitors do not attach to the enzyme's active site where the substrate binds. Instead, they attach somewhere else, changing the enzyme's shape. This change in shape makes the enzyme unable to work properly, even if a substrate is present.

🎯 Exam Tip: Differentiate between competitive (binds at active site) and non-competitive (binds elsewhere, changes shape) inhibitors; this distinction is crucial for understanding enzyme regulation.

 

Question 7. Which enzyme was obtained in a crystalline form first of all?
(a) Urease
(b) Catalase
(c) Amylase
(d) Aldolase
Answer: (a) Urease
In simple words: Urease was the first enzyme successfully turned into crystals. This was a big step in understanding enzymes better. It showed that enzymes are actually proteins, which was a new idea at the time.

🎯 Exam Tip: Knowing historical breakthroughs, like the crystallization of urease by James B. Sumner, helps in understanding the scientific progression of enzymology.

Rbse Class 12 Biology Chapter 9 Very Short Answer Questions

 

Question 1. Who proposed lock and key theory and when was it proposed.
Answer: Emil Fisher (1898). This theory explains how enzymes and substrates fit together perfectly, much like a specific key fits into a specific lock.
In simple words: Emil Fisher came up with the lock and key theory in 1898.

🎯 Exam Tip: Remember both the scientist (Emil Fisher) and the year (1898) for this foundational theory in enzymology.

 

Question 2. The protein part and non-protein part of holoenzyme are called as?
Answer: The protein part is named as apoenzyme, and the non-protein part is called as co-factor. Both parts are necessary for the enzyme to be fully active.
In simple words: The protein part is called apoenzyme, and the non-protein part is called a co-factor.

🎯 Exam Tip: Clearly define apoenzyme and co-factor and mention their combined form, holoenzyme, to show complete understanding.

 

Question 3. Name a nonprotein enzyme.
Answer: Ribozyme enzyme is made up of RNA and is the only non-proteinaceous enzyme known so far. Ribozymes show catalytic activity, similar to protein enzymes.
In simple words: A ribozyme is an enzyme that is not made of protein; it is made of RNA.

🎯 Exam Tip: While most enzymes are proteins, ribozymes are a key exception that can often be overlooked. Highlighting them shows depth of knowledge.

 

Question 4. Define the prosthetic group.
Answer: When the non-protein part of an enzyme is an organic substance and is firmly attached to the protein, it cannot be separated from it easily. This tightly bound organic part is called the prosthetic group. For example, the heme group in hemoglobin is a prosthetic group.
In simple words: A prosthetic group is an organic, non-protein part of an enzyme that is strongly attached to the protein part and cannot be removed easily.

🎯 Exam Tip: Emphasize that a prosthetic group is organic and *firmly* attached, distinguishing it from other co-factors like coenzymes which are often loosely bound.

Rbse Class 12 Biology Chapter 9 Short Answer Questions

 

Question 2. What do you understand by competitive inhibition? How this can be stopped.
Answer: Competitive inhibition happens when a chemical substance, very similar in structure to the normal substrate, tries to attach to the enzyme's active site. This substance competes with the actual substrate, which reduces the enzyme's activity. This type of inhibition can be stopped by increasing the concentration of the actual substrate molecules. More substrate means the normal reaction is more likely to occur.
In simple words: Competitive inhibition is when a fake substrate blocks the enzyme's active site. You can stop it by adding a lot more of the real substrate.

🎯 Exam Tip: Focus on the "competition" for the active site and the reversibility of this inhibition by increasing substrate concentration.

 

Question 3. Briefly explain the method of nomenclature of enzymes.
Answer: There are several ways to name enzymes:
• Most enzymes are named by adding the suffix "-ase" to the end of the name of the substrate they act upon. For example, "Maltase" acts on maltose, "Sucrase" acts on sucrose, and "Urease" acts on urea.
• Many enzymes are also named based on the type of chemical reaction they help to catalyze. For instance, "Oxidase" enzymes are involved in oxidation reactions, and "Dehydrogenase" enzymes help remove hydrogen atoms.
• In more modern naming systems, the suffix "-ase" is added after both the name of the substrate and the type of reaction. An example is "Succinate dehydrogenase," which acts on succinate and helps in a dehydrogenation reaction.
• Some older, traditional names for enzymes are still used today, such as "Pepsin," "Trypsin," and "Chymotrypsin." These names were given before systematic naming rules were established.
• The International Union of Biochemistry (IUB) has created a systematic way to name enzymes. This system assigns a unique code number to each enzyme, which includes information about the substrate, the type of reaction catalyzed, and other details. This ensures a clear and consistent way to identify enzymes globally.
In simple words: Enzymes are named in a few ways: by adding "-ase" to the substrate name (like Maltase), by the reaction type (like Oxidase), by combining both, or using old traditional names like Pepsin. The IUB also uses a special code number for each enzyme.

🎯 Exam Tip: Provide at least three distinct methods of enzyme nomenclature with specific examples to demonstrate a comprehensive understanding.

 

Question 4. How the rate of enzyme activity is accelerated.
Answer: The rate of enzyme activity can be accelerated when a factor that limits it is increased. For instance, if the substrate concentration becomes a limiting factor, increasing it will speed up the reaction. Enzymes work faster when there are enough substrates for them to act on.
In simple words: You can make enzymes work faster by increasing factors that are in short supply, like adding more of the substance they need to change (substrate).

🎯 Exam Tip: When discussing acceleration of enzyme activity, link it directly to increasing the concentration of a limiting factor, such as substrate or enzyme itself.

Rbse Class 12 Biology Chapter 9 Essay Type Questions

 

Question 1. Describe the structure of the enzyme and explain their specific characteristics.
Answer: Enzymes are complex biological molecules, mostly proteins, that act as catalysts in living organisms. Their structure and characteristics are vital for their function:
1. All enzymes are made up of proteins, but not all proteins act as enzymes. Proteins have many other roles in the body besides catalysis.
2. Many enzymes are composed solely of protein and are known as simple enzymes.
3. In some enzymes, a non-protein part is also associated with the protein part. These are called conjugated enzymes or holoenzymes.
4. The protein part of a conjugated enzyme is known as the apoenzyme.
5. The non-protein part of the conjugated enzyme is called a co-factor.
6. Co-factors can be further classified into three main types:
• Prosthetic Group: This is an organic compound that is very tightly bonded to the apoenzyme and cannot be separated easily without damaging the protein. For example, Cytochrome and Flavoprotein use prosthetic groups. These groups are essential for the enzyme's catalytic activity.
• Co-enzyme: These are also organic substances, but they are loosely attached to the apoenzyme. They often act as carriers for specific chemical groups or electrons during reactions. Examples include Co-A, NAD, NADP, and FAD.
• Activator: These are inorganic substances, usually metal ions (like K, Cu, Mn, Fe, Zn, Ca). They help form a bridge between the enzyme and the substrate molecule, aiding in the binding process and increasing enzyme activity.Note: The main protein part of the holoenzyme (conjugated enzyme) is called apoenzyme. Its size and amino acid sequence vary among different enzymes. Proteins are colloidal, giving them a large surface area. The protein part contains active sites where substrate molecules bind for enzymatic activity. In a conjugated enzyme, the enzymatic activity comes from the holoenzyme. Neither the apoenzyme alone nor the non-protein part alone can act as an enzyme.
In simple words: Enzymes are mostly proteins with a special shape. Some enzymes are just protein, while others (holoenzymes) have a protein part (apoenzyme) and a non-protein part (co-factor). Co-factors can be tightly stuck on (prosthetic group), loosely attached (co-enzyme), or simple metal helpers (activators). The whole enzyme needs both parts to work.

🎯 Exam Tip: Clearly define and differentiate between apoenzyme, co-factor (prosthetic group, coenzyme, activator), and holoenzyme, explaining how they combine for function. A simple diagram can help illustrate these parts.

 

Question 2. Describe mechanisms of enzymatic action.
Answer: Enzymes are large molecules with many specific areas on their surface called active sites. These sites are crucial for enzymatic action. The mechanism of enzyme action involves several steps:
• Formation of Enzyme-Substrate Complex (ESC): During enzymatic activity, substrate molecules bind to these active sites on the enzyme. This binding forms an unstable intermediate called the enzyme-substrate complex. This is the first step where the enzyme and substrate interact.
• Lowering of Activation Energy: The formation of the enzyme-substrate complex helps to reduce the activation energy needed for the chemical reaction. Activation energy is the minimum energy required for a reaction to start. By lowering this energy, enzymes speed up the reaction significantly. This is why reactions can occur at body temperature, whereas normally they would need very high temperatures.
• Product Formation and Release: Once the substrate binds and the reaction occurs at the active site, new chemical bonds are formed or broken, turning the substrate into product(s). The product(s) then detach from the enzyme, and the enzyme becomes free to bind with new substrate molecules, repeating the process.

There are two main models explaining how enzymes bind to substrates:
1. Lock and Key Model: Proposed by Emil Fisher, this model suggests that the enzyme's active site has a rigid, specific shape that exactly matches the shape of its substrate, like a key fitting into a specific lock.
2. Induced Fit Model Theory: Proposed by Daniel Koshland, this theory suggests that the enzyme's active site is not rigid but flexible. It can change its shape slightly to fit the substrate more precisely when the substrate binds. This is like a hand fitting into a glove, where the glove (enzyme) adjusts to the hand (substrate). This model better explains how enzymes can accommodate various but specific substrates.
The general process involves the enzyme and substrate combining to form an unstable complex, which then quickly dissociates into the product and the free enzyme, allowing the enzyme to be reused.

In simple words: Enzymes are big molecules with special spots called active sites. They work by grabbing onto a substance (substrate) to form a temporary complex. This helps reactions happen much faster by lowering the energy needed to start them. After the reaction, the enzyme lets go of the new product and is ready to work again. The lock-and-key model says enzymes and substrates fit perfectly. The induced-fit model says the enzyme changes shape a little to fit better when the substrate comes near.

🎯 Exam Tip: When explaining enzyme mechanisms, include details about active sites, enzyme-substrate complex formation, reduction in activation energy, and the Lock and Key as well as the Induced Fit models.

 

Question 3. Explain in details, classficiation of enzymes.
Answer: The International Union of Biochemistry (IUB) has established a detailed system for classifying enzymes into six main categories, based on the type of reaction they catalyze:
1. Oxidoreductases: These enzymes are involved in oxidation-reduction reactions. They either remove or add hydrogen, oxygen, or electrons to a substrate, thus causing oxidation or reduction.
• Oxidases: Transfer hydrogen from the substrate to oxygen. Example: Cytochrome oxidase, Ascorbic acid oxidase.
\( \text{A.H}_2 + \frac{1}{2} \text{O}_2 \implies \text{A} + \text{H}_2\text{O} \)
\( \text{A.H}_2 + \text{O}_2 \implies \text{A} + \text{H}_2\text{O}_2 \)
(A = Substrate)
• Dehydrogenases: Remove hydrogen from the substrate molecule. Example: Lactate dehydrogenase, Alcohol dehydrogenase.
\( \text{A. H}_2 \implies \text{A} + 2\text{H}^+ \)
• Reductases: Add hydrogen or electrons to the substrate and remove oxygen.
\( \text{NO}_3 + \text{NAD H}_2 \implies \text{NO}_2 + \text{NAD}^+ + \text{H}_2\text{O} \)
2. Transferases: These enzymes move a specific functional group (like amino, phosphate, methyl, or ketone) from one molecule to another. Example: Transphosphatase, Transaminase. These are crucial for building complex molecules.
3. Hydrolases: These enzymes break down compounds by adding water (hydrolysis). They break various bonds and typically cleave large substrates into smaller molecules. Digestive enzymes belong to this group. Example: Lipase, Amylase.
4. Lyases: These enzymes catalyze the removal of a group from their substrate molecules, forming a double bond, or by adding a group to a double bond. They achieve this without involving hydrolysis or oxidation. Example: Aldolase. They often create or break double bonds.
5. Isomerases: These enzymes rearrange atoms within a single molecule, converting a substrate into its isomer (a molecule with the same chemical formula but different structure). Example: Phosphohexoisomerase. This ensures proper molecular shapes for biological processes.
6. Ligases or Synthetases: These enzymes join two molecules together, usually using energy from ATP hydrolysis, by forming new covalent bonds. Example: Pyruvate carboxylase, Citrate synthetase. They are important for synthesis reactions in the cell.
In simple words: Enzymes are grouped into six main types based on what kind of reaction they speed up. Oxidoreductases move electrons, Transferases move parts of molecules, Hydrolases break things with water, Lyases break things without water, Isomerases change a molecule's shape, and Ligases join molecules together. Each group has a special job in the body.

🎯 Exam Tip: For each enzyme class, clearly state the type of reaction it catalyzes and provide at least one specific example. Understanding the 'action' word in each class (e.g., 'oxido-reductase' for oxidation-reduction) helps recall its function.

 

Question 4. What is enzyme inhibition? How many types of enzyme inhibition is known? Explain how the effect of inhibitors can be stopped.
Answer: Enzyme inhibition is the process where a chemical substance (an enzyme inhibitor) reduces or completely stops the activity of an enzyme. These inhibitors are not substrate molecules themselves.
Enzyme inhibition is primarily of two types:
1. Competitive Inhibition: In this type, the inhibitor molecule has a structure very similar to the enzyme's natural substrate. It competes with the substrate to bind to the enzyme's active site. If the inhibitor binds, it blocks the substrate from binding, thus reducing enzyme activity. The effect of competitive inhibitors can be overcome by increasing the concentration of the substrate. If there are many more substrate molecules than inhibitor molecules, the substrate is more likely to bind to the active site.
2. Non-Competitive Inhibition: Here, the inhibitor does not resemble the substrate and does not bind to the active site. Instead, it binds to a different site on the enzyme, called the allosteric site. This binding causes a change in the enzyme's overall shape, including the active site. This structural change means the enzyme can no longer bind effectively with its substrate or catalyze the reaction. Such inhibitors often act as poisons, permanently blocking or destroying the active site. Examples include heavy metal ions like \( \text{Pb}^{++} \), \( \text{Hg}^{++} \), and \( \text{Ag}^{++} \). The effect of non-competitive inhibitors typically *cannot* be overcome by simply increasing the substrate concentration, because the active site itself is altered. However, the source states that the effect of some non-competitive inhibitors *can* be overcome by increasing the concentration of the enzyme. A classic example of non-competitive inhibition is cyanide poisoning, which denatures cytochrome oxidase.
In simple words: Enzyme inhibition is when something slows down or stops an enzyme from working. There are two main types: competitive, where a fake molecule blocks the enzyme's active spot (can be fixed by adding more real substance), and non-competitive, where a molecule changes the enzyme's shape from somewhere else, making it not work (harder to fix).

🎯 Exam Tip: Clearly define both competitive and non-competitive inhibition, highlighting the difference in binding site, structural impact, and reversibility by substrate concentration. Mentioning specific examples (like heavy metals for non-competitive) adds value.

Rbse Class 12 Biology Chapter 9 Multiple Choice Questions

 

Question 1. In what respect enzymes are different from catalysts?
(a) High diffusion rate
(b) Active at high temperature
(c) Protein nature
(d) Used in the reaction
Answer: (c) Protein nature
In simple words: Enzymes are special because they are made of protein, unlike general catalysts which can be other types of chemicals. This protein structure makes them very specific in what they do.

🎯 Exam Tip: Remember that while both enzymes and catalysts speed up reactions, enzymes are biological catalysts with a protein structure, making them sensitive to temperature and pH, and highly specific.

 

Question 2. The non-protein part of holoenzyme is called?
(a) Apoenzyme
(b) Co-factor
Answer: (b) Co-factor
In simple words: A holoenzyme is like a complete, working enzyme. It has two parts: a protein part called apoenzyme, and a non-protein part called a co-factor, which helps it work.

🎯 Exam Tip: Distinguish between apoenzyme (protein part), co-factor (non-protein part), and holoenzyme (the complete active enzyme). Knowing these terms is crucial for understanding enzyme function.

 

Question 3. Which of the following statement is absolutely correct?
(a) All proteins are enzymes
(b) All enzymes are proteins
(c) Most enzymes are proteins
(d) None of the options
Answer: (c) Most enzymes are proteins
In simple words: Almost all enzymes are proteins, but not all proteins are enzymes. Some special enzymes like ribozymes are not proteins.

🎯 Exam Tip: This is a common trick question. While the vast majority of enzymes are proteins, there are exceptions like catalytic RNA (ribozymes). Be precise with your understanding of biological molecules.

 

Question 4. Which enzyme was discovered first of all?
(a) Zymase
(b) Lipase
(c) Pepsin
(d) Isomerase
Answer: (a) Zymase
In simple words: The enzyme Zymase was the first one to be found. It helps in the process where sugar turns into alcohol.

🎯 Exam Tip: Knowing historical facts about discoveries can sometimes be asked. Remember that Eduard Buchner discovered zymase from yeast extracts.

 

Question 5. Enzyme activity is affected by -
(a) pH only
(b) Substrate concentration
(c) only temperature
(d) All of the options
Answer: (d) All of the options
In simple words: How well an enzyme works depends on many things, like the acid level (pH), how much substrate is available, and the temperature. All these factors play a role.

🎯 Exam Tip: Enzyme activity is sensitive to environmental conditions. Factors like pH, temperature, and substrate concentration all influence the rate of enzymatic reactions.

 

Question 6. Non-Competitive inhibitors are the substances which?
(a) Combine to the active sites of the enzyme
(b) Decrease the active sites of the enzyme
(c) Change the structural organisation of the enzyme
(d) Change in the properties of an enzyme
Answer: (c) Change the structural organisation of the enzyme
In simple words: Non-competitive inhibitors attach to an enzyme at a different spot than the active site. This changes the enzyme's shape, making it unable to work properly.

🎯 Exam Tip: Differentiate between competitive and non-competitive inhibitors. Competitive inhibitors bind to the active site, while non-competitive inhibitors bind elsewhere, causing a conformational change.

 

Question 7. Which enzyme was obtained in a crystalline form first of all?
(a) Urease
(b) Catalase
(c) Amylase
(d) Aldolase
Answer: (a) Urease
In simple words: Urease was the first enzyme to be crystallized, which means it was purified into a solid, ordered form. This was a big step in studying enzymes.

🎯 Exam Tip: Remember James B. Sumner's work on urease in 1926, which proved that enzymes are proteins and could be crystallized. This was a landmark discovery in biochemistry.

 

Rbse Class 12 Biology Chapter 9 Very Short Answer Questions

 

Question 1. Who proposed lock and key theory and when was it proposed.
Answer: The lock and key theory was proposed by Emil Fisher in 1898. This theory suggests that an enzyme and its substrate fit together perfectly, like a specific key fits into a specific lock.
In simple words: Emil Fisher came up with the lock and key idea in 1898. It explains that enzymes and the chemicals they work on fit together perfectly, just like a key in a lock.

🎯 Exam Tip: For theories, always mention the scientist and the year of proposal. This adds precision to your answer.

 

Question 2. The protein part and non-protein part of holoenzyme are called as?
Answer: The protein part of a holoenzyme is called an apoenzyme, and its non-protein part is known as a co-factor. Both parts are necessary for the enzyme to be fully active.
In simple words: The protein part of an enzyme is an apoenzyme. The non-protein part that helps it work is a co-factor.

🎯 Exam Tip: Clearly define apoenzyme and co-factor, and then state how they combine to form a functional holoenzyme. This shows a complete understanding.

 

Question 3. Name a nonprotein enzyme.
Answer: Ribozyme is an example of a non-protein enzyme. It is made up of RNA and is the only known enzyme that is not protein-based. Ribozymes show catalytic activity like protein enzymes.
In simple words: A ribozyme is an enzyme that is not a protein. It is made of RNA and can help speed up reactions.

🎯 Exam Tip: While most enzymes are proteins, remember the exception: ribozymes are RNA molecules with catalytic activity. This is an important detail.

 

Question 4. Define the prosthetic group.
Answer: A prosthetic group is an organic, non-protein part of an enzyme that is very tightly bound to the protein part (apoenzyme). It is so strongly attached that it cannot be easily removed without damaging the protein itself. These groups are vital for the enzyme's function.
In simple words: A prosthetic group is a special helper molecule, not a protein, that is strongly stuck to an enzyme. It is needed for the enzyme to work right.

🎯 Exam Tip: Emphasize "organic substance" and "firmly attached" when defining a prosthetic group, as these are its key distinguishing features from other co-factors.

 

Rbse Class 12 Biology Chapter 9 Short Answer Questions

 

Question 2. What do you understand by competitive inhibition? How this can be stopped.
Answer: Competitive inhibition happens when a chemical substance, very similar in shape to the original substrate molecule, competes to bind to the enzyme's active site. This reduces how effectively the enzyme can work. This type of inhibition can be reduced or stopped by increasing the amount of the original substrate molecules. By adding more substrate, the inhibitor has a lower chance of binding to the active site.
In simple words: Competitive inhibition is when a fake chemical blocks an enzyme's active spot, stopping the enzyme from working. You can fix this by adding more of the real chemical so it has a better chance to bind.

🎯 Exam Tip: Focus on the "competition" aspect and the structural similarity between the inhibitor and substrate. Also, mention that it's reversible by increasing substrate concentration.

 

Question 3. Briefly explain the method of nomenclature of enzymes.
Answer: Enzymes are named using several methods to make them easy to identify. These methods include:

• Most enzymes are named by adding "-ase" to the end of the name of the substance they act upon (substrate). For example, "Maltase" acts on maltose.
• Some enzymes are named based on the type of reaction they help to catalyze. For instance, "Oxidase" enzymes help in oxidation reactions.
• A more modern naming method adds "-ase" after both the substrate's name and the type of reaction. An example is "Succinate dehydrogenase."
• Traditional names, like "Pepsin" and "Trypsin," are still used for some well-known enzymes.
• The International Union of Biochemistry (IUB) has a systematic way of naming enzymes using a specific code number. This system includes details about the substrate, reaction type, and other information, providing a universal naming standard.

In simple words: Enzymes are named in a few ways. Some are named after what they act on (like Maltase from maltose), some by what they do (like Oxidase for oxidation), and some have older, common names like Pepsin. There is also a formal numbering system for scientific use.

🎯 Exam Tip: When explaining enzyme nomenclature, provide clear examples for each method. Mentioning the IUB system shows comprehensive knowledge.

 

Question 4. How the rate of enzyme activity is accelerated.
Answer: The rate of enzyme activity can be significantly accelerated by ensuring optimal conditions and sufficient substrate. If the substrate concentration becomes a limiting factor, meaning there isn't enough substrate for all the available enzymes to work on, the reaction rate will slow down. In such cases, the reaction rate can be increased by providing more substrate, allowing more enzyme active sites to be occupied and catalyze reactions. Enzymes effectively speed up reactions by lowering the activation energy needed for the reaction to occur.
In simple words: Enzymes work faster when there's enough of the material they act on (substrate). If there's too little substrate, the enzyme works slowly. Adding more substrate helps speed up the reaction because the enzymes have more to do.

🎯 Exam Tip: Discussing the effect of substrate concentration and the concept of a limiting factor is essential here. You can also briefly mention optimal temperature and pH as factors influencing enzyme activity.

 

Rbse Class 12 Biology Chapter 9 Essay Type Questions

 

Question 1. Describe the structure of the enzyme and explain their specific characteristics.
Answer: Enzymes are biological catalysts, mostly made of proteins, that speed up biochemical reactions without being consumed themselves. Their structure and specific characteristics are crucial to their function:

1. Almost all enzymes are proteins, but it's important to remember that not all proteins function as enzymes.
2. Many enzymes consist solely of protein molecules and are known as simple enzymes.
3. However, some enzymes include a non-protein part in addition to their protein component, and these are called conjugated enzymes or holoenzymes.
4. The protein part of a conjugated enzyme is specifically termed an apoenzyme.
5. The non-protein part of a conjugated enzyme is known as a co-factor, which helps the enzyme function.
6. These co-factors can be further categorized into three main types: prosthetic groups, co-enzymes, and activators.

A conjugated enzyme, or holoenzyme, is essentially the apoenzyme combined with its co-factor (Holoenzyme = Apoenzyme + Co-factor).

**1. Prosthetic Group:** This is an organic, non-protein compound that is very tightly bound to the apoenzyme. It cannot be easily separated without causing damage to the protein itself. For example, Cytochrome and Flavoprotein contain prosthetic groups.

**2. Co-enzyme:** These are also organic, non-protein molecules that are loosely attached to the apoenzyme. They often act as carriers of atoms or groups of atoms during the reaction. Examples include Co-A, NAD, NADP, and FAD.

**3. Activator:** These are inorganic substances, usually metal ions, that help to link the enzyme to its substrate molecule. They prepare the enzyme for its catalytic role. Examples include ions like \( K^+ \), \( Cu^{++} \), \( Mn^{++} \), \( Fe^{++} \), \( Zn^{++} \), and \( Ca^{++} \).

The main part of a holoenzyme, or conjugated enzyme, is protein and is called the apoenzyme. The size and amino acid sequence of protein molecules can vary greatly among different enzymes. Enzymes have very specific three-dimensional structures.

• Since proteins are colloidal, they have a large surface area for their reactions.
• The protein part of the enzyme has one or more specific regions called active sites, where substrate molecules attach during the enzymatic reaction.
• In a conjugated enzyme, the overall enzyme activity is carried out by the holoenzyme (the complete active form).
• Neither the apoenzyme nor the non-protein part can function alone as an enzyme. They need each other to work.

In simple words: Enzymes are mostly proteins, but some also have a non-protein part called a co-factor. Together, they form a complete enzyme (holoenzyme). Co-factors can be tightly bound (prosthetic groups), loosely bound (co-enzymes), or metal ions (activators). Enzymes have specific active sites where other molecules attach, and they need all their parts to work.

🎯 Exam Tip: Structure your answer clearly by first defining enzymes, then breaking down holoenzyme into its components (apoenzyme and co-factor), and finally detailing the types of co-factors with examples. Include key characteristics like active sites and specificity.

 

Question 2. Describe mechanisms of enzymatic action.
Answer: All enzymes are large molecules with many specific areas on their surface known as active sites. The way an enzyme works depends on both its own nature and the substrate molecule it acts upon. The main steps involved in enzymatic action are:

**1. Formation of Enzyme-Substrate Complex (ESC):**
In enzyme-catalyzed reactions, the enzyme and the substrate temporarily join together to create an unstable structure called the enzyme-substrate complex (ESC). This complex quickly breaks down to form the product and release the enzyme, ready to catalyze another reaction.
\( \text{Enzyme} + \text{Substrate} \rightarrow \text{Enzyme substrate complex} \)
\( \text{Enzyme substrate complex} \rightarrow \text{Enzyme} + \text{Product(s)} \)


On the surface of each enzyme, specific areas called active sites are found. Substrate molecules attach to these active sites. When the substrate molecules bind at the active sites, they react with each other to form the product. The product then detaches from the enzyme, and the enzyme becomes free to bind with new substrate molecules, repeating the cycle.

**2. Lowering of Activation Energy:**
All chemical reactions need a certain amount of energy, called activation energy, to start. Enzymes significantly reduce the activation energy required for a molecule to react. This means that in the presence of an enzyme, reactants are converted into products with much less energy input. On average, enzymes can lower the activation energy by about 65%. This reduction allows reactions that normally need high temperatures outside the cell to occur at the body's atmospheric temperature inside the cell, making life possible.


There are two main theories that explain how the enzyme-substrate complex is formed and the specificity of enzymes:

**1. Lock and Key Model:** This theory, proposed by Emil Fisher, suggests that the enzyme's active site has a rigid, fixed shape, perfectly complementary to the substrate, much like a lock and its specific key. Only the correct substrate (key) can fit into the active site (lock). After the reaction, the product is released, and the enzyme remains unchanged.


**2. Induced Fit Model Theory:** Daniel Koshland proposed this theory in 1966. It suggests that an enzyme's active site is not rigid but flexible. It is not perfectly complementary to the substrate initially. Instead, when a specific substrate molecule gets close to the enzyme, it causes a small change in the active site's shape, making it fit the substrate perfectly. This induced change allows the enzyme and substrate to bind effectively, forming the enzyme-substrate complex. This mechanism helps explain how enzymes can accommodate slightly different substrates or bind more tightly during catalysis.


In simple words: Enzymes work by binding to specific molecules called substrates at a place called the active site, forming a temporary enzyme-substrate complex. This binding helps lower the energy needed for the reaction to happen, speeding it up. The "lock and key" idea says they fit perfectly, while the "induced fit" idea says the enzyme changes shape slightly to fit the substrate better. After the reaction, the enzyme releases the new products and is ready for more.

🎯 Exam Tip: When describing enzyme mechanisms, clearly explain both the Enzyme-Substrate Complex formation and the lowering of activation energy. Illustrating with diagrams or mentioning the Lock and Key and Induced Fit models will earn you extra points.

 

Question 3. Explain in details, classficiation of enzymes.
Answer: The International Union of Biochemistry (IUB) has established a detailed classification system for enzymes based on the types of reactions they catalyze. All enzymes are divided into six main categories:

**1. Oxidoreductases:** These enzymes facilitate oxidation-reduction reactions. They either remove or add hydrogen, oxygen, or electrons to a substrate, thereby causing oxidation or reduction. These can be further divided into:

• **(a) Oxidases:** Transfer hydrogen from the substrate to oxygen, causing oxidation. Example: Cytochrome oxidase.
  \( \text{A.H}_2 + \frac{1}{2} \text{O}_2 \rightarrow \text{A} + \text{H}_2\text{O} \)
  \( \text{A.H}_2 + \text{O}_2 \rightarrow \text{A} + \text{H}_2\text{O}_2 \) (where A = Substrate)
• **(b) Dehydrogenases:** Remove hydrogen from a substrate molecule, leading to its oxidation. Example: Lactate dehydrogenase.
  \( \text{A.H}_2 \rightarrow \text{A} + 2\text{H}^+ \)
• **(c) Reductases:** Add hydrogen or electrons to a substrate and remove oxygen.
  \( \text{NO}_3 + \text{NAD H}_2 \rightarrow \text{NO}_2 + \text{NAD} + \text{H}_2\text{O} \)

**2. Transferases:** These enzymes move a specific group (like an amino, phosphate, methyl, or ketone group) from one molecule to another. Example: Transphosphatase.

**3. Hydrolases:** Hydrolases catalyze reactions where water is added or removed, breaking down various compounds. This group includes many digestive enzymes that break large molecules into smaller ones. Example: Lipase.

**4. Lyases:** These enzymes remove groups from their substrate molecules, forming double bonds or adding groups to double bonds, without using hydrolysis. Example: Aldolase.

**5. Isomerases:** Isomerases reorganize atoms within a single substrate molecule, converting it into an isomer. Example: Phosphohexoisomerase.

**6. Ligases or Synthetases:** These enzymes join two compounds together, often using energy from ATP, by forming new covalent bonds. Example: Pyruvate carboxylase.

Each class plays a vital role in metabolism, ensuring all necessary chemical transformations occur efficiently.
In simple words: Enzymes are put into six main groups based on the kind of job they do. Some (oxidoreductases) help with give-and-take reactions of electrons. Others (transferases) move parts from one molecule to another. Hydrolases break things down using water, while lyases remove groups without water. Isomerases change a molecule's shape, and ligases stick two molecules together.

🎯 Exam Tip: List all six classes of enzymes and provide a concise definition and a relevant example for each. Understanding the reaction type each class catalyzes is key.

 

Question 4. What is enzyme inhibition? How many types of enzyme inhibition is known? Explain how the effect of inhibitors can be stopped.
Answer: Enzyme inhibition is the process where a chemical substance, other than the usual substrate, reduces or completely stops the activity of an enzyme. These substances are called enzyme inhibitors. Inhibition is a crucial regulatory mechanism in biological systems.
Enzyme inhibition is generally known to be of two main types:
**1. Competitive Inhibition:** In this type, the inhibitor molecule looks very similar to the enzyme's natural substrate. It competes directly with the substrate to bind to the enzyme's active site. If the inhibitor binds, it blocks the substrate from binding, thus slowing down or stopping the reaction. This type of inhibition can often be overcome by increasing the concentration of the substrate, giving the natural substrate a higher chance to bind to the active site.
**2. Non-Competitive Inhibition:** Here, the inhibitor does not resemble the substrate and does not bind to the enzyme's active site. Instead, it binds to a different site on the enzyme. This binding causes a change in the enzyme's overall shape, including the active site, making it less effective or completely inactive. These inhibitors can permanently block or destroy the active site and are sometimes called enzyme poisons. Examples include heavy metal ions like lead (\( Pb^{++} \)), mercury (\( Hg^{++} \)), and silver (\( Ag^{++} \)). Cyanide is a well-known non-competitive inhibitor that denatures cytochrome oxidase, an enzyme vital for respiration. The effect of non-competitive inhibitors is generally not reversed by increasing substrate concentration, but can sometimes be mitigated by increasing the concentration of the enzyme itself, if new enzyme molecules are introduced.
The ability to stop inhibition depends on the type. Competitive inhibition is often reversible, while non-competitive inhibition can be much harder to reverse.
In simple words: Enzyme inhibition is when certain chemicals slow down or stop enzymes from working. There are two main kinds: competitive, where a fake molecule blocks the enzyme's active spot, which can be fixed by adding more of the real molecule; and non-competitive, where a chemical changes the enzyme's shape from a different spot, which is harder to fix.

🎯 Exam Tip: Clearly define enzyme inhibition and then distinguish between competitive and non-competitive types. For each type, explain the binding site, the effect on the enzyme, and how (or if) the inhibition can be reversed, providing examples.