This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Biomolecules – Enzymes”.
1. Which of the following best describes a particular enzyme?
a) Chemical catalyst
b) Fibrous protein
c) Highly selective
d) Can be used for various reactions
Explanation: Enzymes are biological catalysts produced by living cells. They differ from other catalysts in being highly selective and specific. Almost all enzymes are globular proteins. They are very specific for a particular reaction and a particular substrate.
2. Enzymes are generally named after the ________
a) compound on which they work
b) compound which they form as product
c) medium in which they act
d) place from where they are derived
Explanation: Enzymes are generally name after the compound or class of compounds on which they work. For example, the catalyst that hydrolyses the reaction of starch (amylum) to glucose is called as amylase.
3. The enzyme which catalyses the conversion of proteins to amino acids is ______
Explanation: Proteases are enzymes that helps in protein catabolism by hydrolysis of peptide bonds. Pepsin and trypsin are the most common proteases, found in the human stomach and pancreas respectively. Both of them are major digestive enzymes.
4. Which of the following is a substrate specific enzyme?
d) Carbonic anhydrase
Explanation: Substrate specific enzymes are those which can act only on one particular compound to give a product(s). For example, maltase acts only on maltose to break the glycosidic linkage between the two glucose units.
5. Enzymes are regarded as ______
Explanation: Enzymes are biological catalysts produced by living cells which catalyse the biochemical reactions in living organisms. Chemically, enzymes are naturally occurring simple or conjugate proteins.
6. Enzymes are basically ______
d) pyrimidine bases
Explanation: Almost all enzymes are globular proteins, which are nothing but very long chains of amino acids residues (>100) and higher molecular mass, or polypeptides.
7. Cellulose is not digestible by humans due to the absence of which of the following enzymes?
Explanation: The enzyme cellulase hydrolyses cellulose into glucose and thereby digests it. However, the human stomach does not produce any enzyme capable of digesting cellulose, and hence it cannot be digested.
8. Enzymes reduce the magnitude of activation energy for a reaction.
Explanation: For example, the activation energy for acid hydrolysis of sucrose is 6.22kJ/mol, while the activation energy is only 2.15kJ/mol when it is hydrolysed in the presence of sucrase.
9. The hydrolysis of lactose can be catalysed only by the enzyme lactase. Also, lactase is only able to work on lactose and no other compound.
Explanation: Enzymes are highly specific in nature. Almost all biochemical reactions ae controlled by its own specific enzyme.
10. The prosthetic groups which get attached to the enzyme at the time of reaction are called _____
Explanation: Most active enzymes are associated with some non-protein components required for their activity. These are called prosthetic groups and they may be cofactors or coenzymes.
11. Albinism is caused by the deficiency of which enzyme?
a) Phenylalanine hydroxylase
Explanation: Deficiency of tyrosinase results in insufficient production of melanin. This causes a condition of white skin and hair called albinism. It can be prevented by including the required supply of enzyme through diet.
12. Identify the correct statement about enzymes.
a) Enzymes increase the activation energy of a reaction
b) Enzymes need to be used in excess compared to the reagent to catalyse the reaction
c) Enzymes work only at their optimum temperature and pH
d) The activity of enzymes cannot be affected by other compounds
Explanation: Enzymes decrease the activation energy of a reaction. Extremely small quantities of enzymes can increase the rate of reaction by thousands. Enzyme action can be inhibited by compounds known as enzyme inhibitors.
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