Chapter 1 Enzyme Properties And Importance

Question 1

1 Enzymes are primarily classified as: (a) Carbohydrates (b) Lipids (c) Proteins (d) Nucleic acids

Answer 1

Answer: (c) Explanation: While some RNA molecules (ribozymes) can act as catalysts the vast majority of enzymes are proteins.

Question 2

2 Which historical event marked the earliest recognition of enzymes? (a) Observation of meat digestion by stomach secretions in the 1700s (b) Discovery of fermentation by yeast cells in the 1800s (c) Isolation and crystallization of urease from jack bean in 1926 (d) X-ray crystallography of lysozyme structure in 1965

Answer 2

Answer: (a) Explanation: The first documented recognition of enzyme activity involved the study of meat digestion by stomach secretions in the late 1700s. This observation led to further research on biological catalysts.

Question 3

3 The specific region of an enzyme where the substrate binds is called: (a) Allosteric site (b) Active site (c) Catalytic domain (d) Binding pocket

Answer 3

Answer: (b) Explanation: The active site is a unique three-dimensional region on the enzyme molecule. It possesses a specific shape and chemical properties that allow it to interact with the substrate.

Question 4

4 Which type of enzyme-substrate interaction involves the attraction between charged groups in the active site and the substrate? (a) Hydrogen bonding (b) Electrostatic interaction (c) Non-polar interaction (d) Hydrophobic interaction

Answer 4

Answer: (b) Explanation: Electrostatic interactions involve the attraction between opposite charges. This type of interaction is crucial for substrate binding and orientation in the active site.

Question 5

5 The scientific argument that “all enzymes do not follow the Michaelis-Menten hypothesis” suggests that: (a) Some enzymes exhibit complex kinetic behavior not fully explained by the model. (b) Enzymes are not always proteins. (c) Metals play no role in enzymatic reactions. (d) Antibodies cannot act as enzymes.

Answer 5

Answer: (a) Explanation: The Michaelis-Menten hypothesis provides a fundamental model for understanding enzyme kinetics. However some enzymes deviate from this model indicating more complex mechanisms are at play.

Question 6

6 What non-protein component can be tightly or loosely bound to an enzyme influencing its activity? (a) Substrate (b) Inhibitor (c) Cofactor (d) Product

Answer 6

Answer: (c) Explanation: Cofactors are non-protein molecules or ions that are required for some enzymes to function. Organic cofactors are called coenzymes. Cofactors can be metal ions (like Fe²+ Mg²+ Zn²+) or complex organic molecules.

Question 7

7 The study of enzymes and enzyme-catalyzed reactions is known as: (a) Enzymology (b) Endocrinology (c) Cytology (d) Histology

Answer 7

Answer: (a) Explanation: Enzymology is a specialized branch of biochemistry that focuses on the structure function kinetics and regulation of enzymes.

Question 8

8 Which of the following is an example of an extracellular enzyme? (a) Enzymes involved in respiration inside the mitochondria (b) Digestive enzymes in the stomach (c) Enzymes involved in DNA replication in the nucleus (d) Enzymes involved in protein synthesis in the ribosomes

Answer 8

Answer: (b) Explanation: Extracellular enzymes are secreted outside the cell and function in external environments. Digestive enzymes like those found in the stomach break down food molecules outside of the cells lining the stomach.

Question 9

9 Which enzyme class catalyzes the joining of two molecules coupled with energy from the hydrolysis of a high-energy bond? (a) Oxidoreductases (b) Transferases (c) Hydrolases (d) Ligases

Answer 9

Answer: (d) Explanation: Ligases catalyze the formation of new bonds between molecules. These reactions are often energetically unfavorable and are coupled with the hydrolysis of high-energy bonds in molecules like ATP.

Question 10

10 What is the optimal temperature range for most human enzymes? (a) 25-30°C (b) 35-40°C (c) 45-50°C (d) 55-60°C

Answer 10

Answer: (b) Explanation: Human enzymes generally function best at normal body temperature which is approximately 37°C. Temperatures outside this range can affect enzyme activity.

Question 11

11 The lowering of activation energy by enzymes is a key factor in: (a) Altering reaction equilibrium (b) Changing the free energy change of a reaction (c) Speeding up the rate of a reaction (d) Making endergonic reactions exergonic

Answer 11

Answer: (c) Explanation: Enzymes act as catalysts facilitating a faster reaction rate by reducing the activation energy needed for the reaction to proceed. They do not affect the overall energy change or equilibrium of the reaction.

Question 12

12 Which statement about enzyme properties is INCORRECT? (a) Enzymes are sensitive to temperature changes. (b) Enzymes are consumed in the reactions they catalyze. (c) Enzymes are proteins. (d) Enzymes are specific for their substrates.

Answer 12

Answer: (b) Explanation: Enzymes are not consumed during the reactions they catalyze. They remain unchanged and can catalyze multiple reactions.

Question 13

13 The ‘induced fit’ model of enzyme action proposes: (a) The active site remains rigid and unchanged upon substrate binding. (b) The active site undergoes conformational changes to accommodate the substrate. (c) The substrate forces the enzyme to denature. (d) Enzyme-substrate interactions are purely electrostatic.

Answer 13

Answer: (b) Explanation: The induced fit model suggests that the active site of an enzyme is not a rigid structure but rather undergoes subtle conformational changes upon substrate binding. These changes enhance the interaction between the enzyme and substrate leading to more efficient catalysis.

Question 14

14 The systematic naming of enzymes involves adding the suffix “-ase” to: (a) The scientist who discovered the enzyme (b) The organism from which the enzyme was first isolated (c) The nature of the reaction catalyzed (d) The substrate on which the enzyme acts

Answer 14

Answer: (c) Explanation: The “-ase” suffix is a standard convention in enzyme nomenclature indicating that the molecule is an enzyme and providing insight into the type of reaction it catalyzes.

Question 15

15 The Enzyme Commission (EC) number assigned to each enzyme: (a) Reflects the enzyme’s molecular weight (b) Indicates the date of the enzyme’s discovery (c) Classifies the enzyme based on the reaction it catalyzes (d) Represents the enzyme’s optimal pH

Answer 15

Answer: (c) Explanation: The EC number is a numerical classification system that categorizes enzymes based on the specific chemical reactions they catalyze. It helps researchers and scientists organize and understand the vast diversity of enzymes

Question 16

1. Enzymes are primarily classified as: (a) Carbohydrates (b) Lipids (c) Proteins (d) Nucleic acids

Answer 16

C.Explanation: While some RNA molecules (ribozymes) can act as catalysts the vast majority of enzymes are proteins.

Question 17

2. Which historical event marked the earliest recognition of enzymes? (a) Observation of meat digestion by stomach secretions in the 1700s (b) Discovery of fermentation by yeast cells in the 1800s (c) Isolation and crystallization of urease from jack bean in 1926 (d) X-ray crystallography of lysozyme structure in 1965

Answer 17

A.Explanation: The first documented recognition of enzyme activity involved the study of meat digestion by stomach secretions in the late 1700s. This observation led to further research on biological catalysts.

Question 18

3. The specific region of an enzyme where the substrate binds is called: (a) Allosteric site (b) Active site (c) Catalytic domain (d) Binding pocket

Answer 18

B.Explanation: The active site is a unique three-dimensional region on the enzyme molecule. It possesses a specific shape and chemical properties that allow it to interact with the substrate.

Question 19

4. Which type of enzyme-substrate interaction involves the attraction between charged groups in the active site and the substrate? (a) Hydrogen bonding (b) Electrostatic interaction (c) Non-polar interaction (d) Hydrophobic interaction

Answer 19

B. Explanation: Electrostatic interactions involve the attraction between opposite charges. This type of interaction is crucial for substrate binding and orientation in the active site.

Question 20

5. The scientific argument that “all enzymes do not follow the Michaelis-Menten hypothesis” suggests that: (a) Some enzymes exhibit complex kinetic behavior not fully explained by the model. (b) Enzymes are not always proteins. (c) Metals play no role in enzymatic reactions. (d) Antibodies cannot act as enzymes.

Answer 20

A. Explanation: The Michaelis-Menten hypothesis provides a fundamental model for understanding enzyme kinetics. However some enzymes deviate from this model indicating more complex mechanisms are at play.

Question 21

6. What non-protein component can be tightly or loosely bound to an enzyme influencing its activity? (a) Substrate (b) Inhibitor (c) Cofactor (d) Product

Answer 21

C.Explanation: Cofactors are non-protein molecules or ions that are required for some enzymes to function. Organic cofactors are called coenzymes. Cofactors can be metal ions (like Fe²+

Question 22

7. The study of enzymes and enzyme-catalyzed reactions is known as: (a) Enzymology (b) Endocrinology (c) Cytology (d) Histology

Answer 22

Answer: AExplanation: Enzymology is a specialized branch of biochemistry that focuses on the structure function kinetics and regulation of enzymes.

Question 23

8. Which of the following is an example of an extracellular enzyme? (a) Enzymes involved in respiration inside the mitochondria (b) Digestive enzymes in the stomach (c) Enzymes involved in DNA replication in the nucleus (d) Enzymes involved in protein synthesis in the ribosomes

Answer 23

Answer: B Explanation: Extracellular enzymes are secreted outside the cell and function in external environments. Digestive enzymes like those found in the stomach break down food molecules outside of the cells lining the stomach.

Question 24

9. Which enzyme class catalyzes the joining of two molecules coupled with energy from the hydrolysis of a high-energy bond? (a) Oxidoreductases (b) Transferases (c) Hydrolases (d) Ligases

Answer 24

Answer: D Explanation: Ligases catalyze the formation of new bonds between molecules. These reactions are often energetically unfavorable and are coupled with the hydrolysis of high-energy bonds in molecules like ATP.

Question 25

10. What is the optimal temperature range for most human enzymes? (a) 25-30°C (b) 35-40°C (c) 45-50°C (d) 55-60°C

Answer 25

Answer: B Explanation: Human enzymes generally function best at normal body temperature which is approximately 37°C. Temperatures outside this range can affect enzyme activity.

Question 26

11. The lowering of activation energy by enzymes is a key factor in: (a) Altering reaction equilibrium (b) Changing the free energy change of a reaction (c) Speeding up the rate of a reaction (d) Making endergonic reactions exergonic

Answer 26

Answer: C Explanation: Enzymes act as catalysts facilitating a faster reaction rate by reducing the activation energy needed for the reaction to proceed. They do not affect the overall energy change or equilibrium of the reaction.

Question 27

12. Which statement about enzyme properties is INCORRECT? (a) Enzymes are sensitive to temperature changes. (b) Enzymes are consumed in the reactions they catalyze. (c) Enzymes are proteins. (d) Enzymes are specific for their substrates.

Answer 27

Answer: B Explanation: Enzymes are not consumed during the reactions they catalyze. They remain unchanged and can catalyze multiple reactions.

Question 28

13. The ‘induced fit’ model of enzyme action proposes: (a) The active site remains rigid and unchanged upon substrate binding. (b) The active site undergoes conformational changes to accommodate the substrate. (c) The substrate forces the enzyme to denature. (d) Enzyme-substrate interactions are purely electrostatic.

Answer 28

Answer: B Explanation: The induced fit model suggests that the active site of an enzyme is not a rigid structure but rather undergoes subtle conformational changes upon substrate binding. These changes enhance the interaction between the enzyme and substrate leading to more efficient catalysis.

Question 29

14. The systematic naming of enzymes involves adding the suffix “-ase” to: (a) The scientist who discovered the enzyme (b) The organism from which the enzyme was first isolated (c) The nature of the reaction catalyzed (d) The substrate on which the enzyme acts

Answer 29

Answer: C Explanation: The “-ase” suffix is a standard convention in enzyme nomenclature indicating that the molecule is an enzyme and providing insight into the type of reaction it catalyzes.

Question 30

15. The Enzyme Commission (EC) number assigned to each enzyme: (a) Reflects the enzyme’s molecular weight (b) Indicates the date of the enzyme’s discovery (c) Classifies the enzyme based on the reaction it catalyzes (d) Represents the enzyme’s optimal pH

Answer 30

Answer: C Explanation: The EC number is a numerical classification system that categorizes enzymes based on the specific chemical reactions they catalyze. It helps researchers and scientists organize and understand the vast diversity of enzymes.

Question 31

16. Which of the following is NOT a factor affecting enzyme action? (a) Temperature (b) pH (c) Enzyme color (d) Substrate concentration

Answer 31

Answer: C Explanation: Enzyme activity is influenced by temperature pH and substrate concentration but color plays no role in their catalytic function.

Question 32

17. The effect of a significant pH change on enzyme activity is primarily due to:(a) Increased substrate concentration(b) Disruption of hydrogen bonds and active site shape (c) Enhanced enzyme-substrate collisions (d) Activation of allosteric sites

Answer 32

Answer: B Explanation: Changes in pH can alter the ionization states of amino acid residues within the enzyme’s active site affecting hydrogen bonding patterns and ultimately distorting the shape of the active site. This can lead to decreased enzyme activity or complete inactivation.

Question 33

18. The role of enzymes in living things includes: (a) Catalyzing metabolic reactions (b) Regulating metabolic pathways (c) Determining cell activity (d) All of the above

Answer 33

Answer: D Explanation: Enzymes are crucial for regulating and controlling virtually all metabolic processes in living organisms from the breakdown of nutrients to the synthesis of complex biomolecules. They play a vital role in maintaining cellular homeostasis.

Question 34

19. The use of biological materials in manufacturing or treatment procedures for commercial or scientific purposes is called: (a) Genetic engineering (b) Bioprocessing (c) Fermentation (d) Cloning

Answer 34

Answer: B Explanation: Bioprocessing encompasses a wide range of biotechnological techniques that utilize biological systems including enzymes for various industrial applications.

Question 35

20. Which example highlights the industrial application of enzymes in food production? (a) Production of fructose from glucose (b) Production of biofuels from algae (c) Synthesis of pharmaceuticals (d) Treatment of wastewater

Answer 35

Answer: A Explanation: The conversion of glucose to fructose using enzymes like glucose isomerase is a common practice in the food industry. Fructose is sweeter than glucose and is often used as a sweetener in various food products.

Question 36

21. Enzyme activity is typically highest at a specific temperature called the: (a) Denaturation temperature (b) Optimum temperature (c) Activation temperature (d) Equilibrium temperature

Answer 36

Answer: B Explanation: The optimum temperature represents the temperature at which an enzyme exhibits its maximum catalytic activity.

Question 37

22. Substances that slow down or inhibit enzyme activity are known as: (a) Activators (b) Inhibitors (c) Cofactors (d) Substrates

Answer 37

Answer: B Explanation: Inhibitors can bind to enzymes either reversibly or irreversibly and reduce or completely block their catalytic activity.

Question 38

23. A holoenzyme refers to: (a) An enzyme without its cofactor (b) A denatured enzyme (c) An enzyme with its cofactor bound (d) An inactive precursor of an enzyme

Answer 38

Answer: C Explanation: A holoenzyme is a complete and catalytically active enzyme consisting of the protein portion (apoenzyme) and any necessary cofactors.