What Are the Types and Functions of Enzymes in Biochemistry?
Practising MCQs on enzymes is essential for mastering biology, especially for Class 11, competitive exams, and foundational biochemistry knowledge. These questions help students reinforce key concepts about enzyme structure, function, inhibition, and classification. Engaging with well-structured multiple choice questions also improves speed, accuracy, and readiness for exams that assess conceptual clarity in topics like restriction enzymes, protein chemistry, and cellular processes.
Overview: Enzymes and Their Biological Role
Enzymes are biological catalysts, mostly proteins, that accelerate biochemical reactions by lowering the activation energy required. Without enzymes, most cellular processes would occur dangerously slowly for life to exist. While most enzymes are proteins, ribozymes (catalytic RNA) are a notable exception. Enzymes are highly specific, reusable, and play vital roles in digestion, metabolism, DNA replication, and environmental systems.
- Enzymes do not get consumed during reactions.
- They do not alter the final equilibrium of reactions.
- Many enzymes require cofactors (metal ions or coenzymes) for activity.
- Enzymes work best within specific temperature and pH ranges.
For a deeper dive into related biomolecules, see What are Biomolecules, and to understand differences with hormones, visit Enzymes vs Hormones.
Practice MCQs on Enzymes (with Answers & Explanations)
This section presents the most important MCQs on enzymes for Class 11, NEET, and foundational biochemistry. Each question is followed by the correct answer and a brief explanation, helping students grasp concepts crucial for board and entrance exams, as well as for a solid understanding of molecular biology.
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The main action of enzymes is to:
A) Reduce activation energy
B) Increase activation energy
C) Decrease pH
D) Increase pH
Answer: A) Reduce activation energy
Explanation: Enzymes accelerate reactions by lowering the energy barrier, helping processes like digestion and cellular respiration proceed efficiently. -
Which of the following is usually a coenzyme?
A) Metal ion
B) Protein
C) Vitamin
D) Inorganic compound
Answer: C) Vitamin
Explanation: Most coenzymes are derived from vitamins or organic molecules, necessary for enzymatic activity. -
The enzyme complex that catalyzes alcoholic fermentation is:
A) Zymase
B) Amylase
C) Lipase
D) Invertase
Answer: A) Zymase
Explanation: Zymase in yeast catalyzes conversion of glucose to ethanol and CO₂, a process crucial to brewing and baking industries. -
Which is the protein portion of an enzyme, absent of its coenzyme?
A) Apoenzyme
B) Holoenzyme
C) Prosthetic group
D) Substrate
Answer: A) Apoenzyme
Explanation: The apoenzyme alone is inactive; activity requires binding of the appropriate cofactor or coenzyme. -
Competitive inhibition of an enzyme means:
A) Inhibitor resembles substrate and blocks active site
B) Inhibitor changes enzyme’s shape
C) Enzyme is consumed
D) Product inhibits enzyme
Answer: A) Inhibitor resembles substrate and blocks active site
Explanation: Molecules like malonic acid can competitively inhibit enzymes (e.g., succinate dehydrogenase) by occupying the active site. For details, see Competitive Inhibition. -
The optimal temperature for enzyme action in the human body is:
A) 15°C
B) 20°C
C) 25°C
D) 37°C
Answer: D) 37°C
Explanation: Enzymes in human physiology work best at normal body temperature, around 37°C, losing efficiency outside this range. -
Which enzyme catalyses the breakdown of starch to maltose?
A) Protease
B) Amylase
C) Lactase
D) Maltase
Answer: B) Amylase
Explanation: Amylase is present in saliva and pancreas, crucial for starch digestion into smaller sugars. -
Which of these statements about enzymes is true?
A) They lower activation energy
B) They are proteins with unique 3D structure
C) They do not alter the overall free energy change
D) All of these
Answer: D) All of these
Explanation: Enzymes have unique shapes, facilitate reactions, and remain unaltered after catalysis. -
Optimum pH value for the enzyme pepsin is:
A) 1.4
B) 2.0
C) 3.5
D) 5.0
Answer: A) 1.4
Explanation: Pepsin is active in the highly acidic environment of the stomach, around pH 1.4–1.6. -
Which is NOT an attribute of enzymes?
A) Specificity
B) Protein within chemistry
C) Consumed in reactions
D) Increased reaction rate
Answer: C) Consumed in reactions
Explanation: Enzymes act as catalysts and are not consumed during biochemical reactions.
For more on enzyme questions for competitive exams, including Class 11 sample MCQs, explore related concepts like cell theory and metabolism.
Types of Enzyme Inhibition: MCQs & Examples
Understanding enzyme inhibition is vital in biochemistry, pharmacology, and medicine. Below are important MCQs on enzyme inhibition, including restriction enzymes used in genetic engineering:
- Competitive Inhibition: Inhibitor competes for active site (e.g., malonic acid for succinate dehydrogenase).
- Non-Competitive Inhibition: Inhibitor binds elsewhere, changing enzyme structure.
- Feedback Inhibition: End-product of a pathway inhibits an upstream enzyme.
- Allosteric Inhibition: Effector molecule binds at a non-active site, altering enzyme conformation.
For detailed differences between restriction endonucleases and exonucleases, see Restriction Endonuclease vs Exonuclease. Application of restriction enzymes is crucial in recombinant DNA technology and genetic research.
Classification of Enzymes (CBSE Class 11 Syllabus 2025-26)
According to the CBSE Class 11 and biochemistry curriculum, enzymes are classified based on the nature of the biochemical reaction they catalyse. This classification is useful for answering MCQs on enzymes class 11 with confidence.
| Enzyme Class | Type of Reaction Catalysed | Example |
|---|---|---|
| Oxidoreductases | Oxidation-Reduction | Dehydrogenases |
| Transferases | Transfer of functional groups | Transaminase |
| Hydrolases | Hydrolytic cleavage (uses water) | Amylase |
| Lyases | Breaking bonds by means other than hydrolysis and oxidation | Aldolase |
| Isomerases | Isomerisation of molecules | Isomerase |
| Ligases | Joining two molecules with input of energy (usually ATP) | DNA Ligase |
This table helps quickly recall enzyme categories, essential for MCQs on enzymes biochemistry and class 11 exams.
Tips to Ace MCQs on Enzymes Class 11
Here are proven strategies to excel at MCQs on enzymes class 11 with answers:
- Thoroughly revise key enzyme properties, such as specificity, the lock-and-key vs induced-fit models, and cofactor types.
- Practice sample questions and previous year MCQs on enzymes biochemistry to build reasoning speed.
- Understand real-world enzyme applications—like restriction enzymes in biotechnology and medicine.
- Study limiting factors affecting enzyme activity: temperature, pH, substrate concentration, and inhibitors.
For extra support in understanding nutrition and digestive enzymes, visit Nutrients and Our Body and Teeth and Digestion. Vedantu offers expert online guidance to streamline your biology revision.
Why Practising Enzyme MCQs Matters
Mastering MCQs on enzymes improves analytical skills, conceptual clarity, and exam confidence. It prepares students for complex biological challenges and applications in medical, environmental, and industrial fields. As enzymes underpin key science and health sectors, solidifying this understanding is valuable beyond the classroom.
For further learning in related fields, explore areas like endocrinology, food science, and biological science at Vedantu.
In conclusion, regular practice of MCQs on enzymes ensures a solid base in life sciences, helps in examinations, and opens doors to understanding advanced biological systems and innovations.
FAQs on MCQs on Enzymes with Answers for Class 11 Biology
1. What are enzymes?
Enzymes are biological catalysts that speed up chemical reactions in living organisms.
- They are mostly proteins, with a few RNA-based enzymes known as ribozymes.
- Enzymes lower the activation energy required for biochemical reactions.
- They are highly specific to their substrates and function under optimal temperature and pH conditions.
2. What is the mode of action of enzymes?
The mode of action of enzymes involves binding to specific substrates to form an enzyme-substrate complex, facilitating a chemical change and releasing products.
- Enzyme-substrate complex formation is central to catalysis.
- Enzymes operate via the lock-and-key or induced fit models.
- This process increases the reaction rate without being consumed.
3. How are enzymes classified?
Enzymes are classified into six main categories based on the type of reaction they catalyse:
- Oxidoreductases: Catalyse oxidation-reduction reactions.
- Transferases: Transfer functional groups.
- Hydrolases: Break bonds with water addition (hydrolysis).
- Lyases: Add or remove groups to form double bonds.
- Isomerases: Catalyse isomerisation changes within a molecule.
- Ligases: Join two molecules using ATP.
4. What is the optimum temperature and pH for enzyme activity?
Optimum temperature and pH are specific conditions where enzyme activity is at its maximum.
- Most human enzymes work best at about 37°C (body temperature).
- The optimum pH varies with each enzyme, e.g., pepsin works best at pH 2, while amylase functions best near pH 7.
5. What factors affect enzymatic activity?
Key factors affecting enzyme activity include:
- Temperature: Enzyme activity increases with temperature up to a limit, then decreases due to denaturation.
- pH: Each enzyme has an optimal pH range.
- Substrate concentration: Activity rises with more substrate, then levels off at saturation.
- Enzyme concentration: Higher enzyme levels increase reaction rates, if substrates are sufficient.
- Presence of inhibitors or activators: Can decrease or enhance enzyme function.
6. What is enzyme inhibition? Name the types.
Enzyme inhibition means decreasing or stopping enzyme activity by inhibitors.
- Competitive inhibition: Inhibitor resembles substrate and competes for the active site.
- Non-competitive inhibition: Inhibitor binds elsewhere, altering enzyme shape and activity.
- Uncompetitive inhibition: Inhibitor binds only to enzyme-substrate complex.
7. Write any two characteristics of enzymes.
Enzymes have important characteristics such as:
- Specificity: Each enzyme acts only on specific substrates.
- Catalytic efficiency: Enzymes increase reaction speed without being used up.
8. What is the difference between cofactor and coenzyme?
Cofactors and coenzymes assist enzymes in catalysis but differ in structure.
- Cofactors: Non-protein, may be inorganic (like Mg²⁺, Zn²⁺).
- Coenzymes: Organic molecules, often derived from vitamins (like NAD⁺, FAD).
- Both are essential for proper enzyme function.
9. What are active site and allosteric site?
Active site is the region of the enzyme where the substrate binds, while the allosteric site is a separate site where molecules can regulate enzyme activity.
- Active site: Specific to substrate, responsible for catalysis.
- Allosteric site: Binding here can increase or decrease enzyme activity by changing enzyme shape.
10. What is the significance of enzymes in living organisms?
Enzymes are essential for sustaining life by controlling all biochemical reactions.
- Enable metabolic reactions like digestion, respiration, and DNA replication.
- Ensure reactions occur at a speed necessary for life processes.
- Allow cellular regulation and adaptation to environmental changes.
11. What is Michaelis-Menten constant (Km)?
Michaelis-Menten constant (Km) is the substrate concentration at which enzyme achieves half its maximum velocity (Vmax).
- A low Km means high substrate affinity.
- It is an important parameter in enzyme kinetics studies.
12. Explain the lock and key model of enzyme action.
The lock and key model suggests that the enzyme's active site (lock) is exactly shaped to fit the substrate (key).
- Only specific substrates fit the active site, leading to reaction.
- This model highlights enzyme specificity.
