CUET UG Chemistry Booster Test – 3 Enzymes and Vitamins

Enzymes are biocatalysts that accelerate biochemical reactions by lowering the activation energy required for the reaction. This allows metabolic processes such as digestion, respiration and biosynthesis to occur efficiently at normal body temperature and physiological pH. Without enzymes, these reactions would be too slow to sustain life. Therefore, option B is the correct answer.

Statement 2 is correct because most enzymes are naturally occurring globular proteins composed of folded polypeptide chains. Statement 4 is also correct because these polypeptide chains fold into a compact three-dimensional spherical structure, making enzymes water-soluble and functionally active. Statement 1 is incorrect because enzymes are proteins rather than carbohydrates. Statement 3 is incorrect because enzymes are highly efficient catalysts and are required only in small amounts.

Enzyme specificity means that each enzyme acts only on a particular substrate; for example, maltase hydrolyses only maltose. Most enzymes are globular proteins, making them soluble in water. As biocatalysts, enzymes lower the activation energy of reactions, thereby increasing the reaction rate. Because of this reduced activation energy, biochemical reactions occur efficiently at normal body temperature and physiological conditions. Therefore, the correct matching is 1-b, 2-a, 3-d and 4-c.

A reaction without any catalyst requires the maximum activation energy because there is no mechanism to lower the energy barrier. Acid catalysts reduce the activation energy, making the reaction proceed faster than the uncatalysed reaction. Enzymes are highly efficient biological catalysts that lower the activation energy even more effectively than ordinary acid catalysts. Therefore, the decreasing order of activation energy is (C) > (A) > (B).

Activation energy is the minimum amount of energy required for reactant molecules to form the activated complex and proceed to products. Since it represents energy per mole of reactants, it is expressed in kilojoules per mole (kJ mol⁻¹). Therefore, the reduction in activation energy brought about by sucrase is measured in kJ mol⁻¹, making option C correct.

Enzymes accelerate biochemical reactions by lowering the activation energy required to reach the transition state. They provide an alternative reaction pathway that requires less energy, allowing reactions to proceed rapidly under physiological conditions. Enzymes do not alter the equilibrium of the reaction, nor are they permanently changed during catalysis. Therefore, option B is correct.

Most enzymes are named by adding the suffix "-ase" to the name of the substrate on which they act. Since the substrate is xylulose, the enzyme would be named Xylulase. The other options include unnecessary reaction classifications or do not follow the standard naming convention. Therefore, option C is correct.

Oxidoreductases catalyse oxidation-reduction (redox) reactions in which one substance loses electrons (oxidation) while another gains electrons (reduction). Since electron transfer always involves both oxidation and reduction occurring simultaneously, option B is correct.

The original term "Vitamine" was coined because the first discovered vitamins were believed to contain amino (amine) groups. However, further research established that most vitamins do not possess amino groups in their chemical structure. Since the presence of an amine group is not a common feature of all vitamins, the letter "e" was dropped, and the term "vitamin" became the accepted name. Therefore, option B is correct.

The passage states that although vitamins are generally required in the diet, certain bacteria present in the human gut synthesize some of the vitamins required by the body, such as vitamin K and certain B-complex vitamins. This means that the statement claiming all vitamins must come exclusively from external dietary sources is not entirely correct. Hence, Option B is the correct answer.

Fat-soluble vitamins (A, D, E and K) dissolve in fats and are stored in the liver and adipose tissues instead of being rapidly excreted. Continuous excessive intake can lead to their accumulation in the body, resulting in toxicity known as hypervitaminosis. Water-soluble vitamins, on the other hand, are generally excreted through urine, making toxicity less common. Therefore, option C is correct.

B-complex vitamins and Vitamin C are water-soluble and are generally not stored in the body (except Vitamin B12). Since excess amounts are readily excreted through urine, they must be supplied regularly through a balanced diet to maintain normal physiological functions. Therefore, option C is correct.

Statement 2 is correct because Vitamin K is essential for the synthesis of blood-clotting factors, and its deficiency increases blood clotting time. Statement 3 is correct because the skin synthesizes Vitamin D when exposed to sunlight. Statement 4 is correct because Vitamin A deficiency causes night blindness due to impaired vision in dim light. Statement 1 is incorrect because Vitamin E is a fat-soluble vitamin, not a water-soluble vitamin. Therefore, the correct combination is 2, 3 and 4.

Fat-soluble vitamins (A, D, E and K) are insoluble in water but readily dissolve in fats and oils. Because of this property, they accumulate in lipid-rich tissues such as adipose tissue and the liver, allowing them to be stored for long periods. Therefore, option B is correct.

Vitamin B12 (Cobalamin) is essential for normal red blood cell formation and DNA synthesis. Deficiency of Vitamin B12 leads to pernicious anaemia, characterized by impaired production of healthy red blood cells. Therefore, option D is correct.

Ascorbic acid (Vitamin C) is a water-soluble vitamin that cannot be stored in the body for long periods. Excess amounts are readily excreted through urine, making regular dietary intake necessary. This property distinguishes it from fat-soluble vitamins, which are stored in the liver and adipose tissues. Therefore, option B is correct.

Vitamin E acts as an antioxidant that protects red blood cell membranes; its deficiency increases RBC fragility. Vitamin B1 (Thiamine) deficiency causes beri beri, characterized by retarded growth, weakness and loss of appetite. Vitamin D deficiency impairs bone mineralization, leading to bone deformities such as rickets in children. Vitamin C deficiency causes scurvy, a characteristic symptom of which is bleeding gums due to defective collagen synthesis. Therefore, the correct matching is 1-d, 2-a, 3-c and 4-b.

Statement 1 is correct because Riboflavin (Vitamin B2) deficiency causes cheilosis, characterized by fissuring at the corners of the mouth. Statement 2 is correct because xerophthalmia, caused by Vitamin A deficiency, involves drying and hardening of the cornea. Statement 3 is correct because Vitamin B6 (Pyridoxine) deficiency can lead to neurological symptoms such as convulsions. Statement 4 is incorrect because pernicious anaemia results from Vitamin B12 deficiency and is characterized by defective red blood cell formation, not excess haemoglobin. Therefore, the correct answer is Option B.

Citrus fruits and amla are excellent sources of Vitamin C. Vitamin D is synthesized in the skin upon exposure to sunlight and is also present in egg yolk. Vegetable oils, especially wheat germ oil, are rich in Vitamin E. Green leafy vegetables are the major dietary source of Vitamin K. Therefore, the correct matching is 1-d, 2-c, 3-b and 4-a.

Human cells lack the metabolic pathways to synthesize most vitamins. Plants, however, are capable of synthesizing almost all vitamins and therefore serve as the primary natural source of these essential nutrients. Consequently, humans depend largely on plant foods, either directly or indirectly through animals, to obtain adequate vitamins. Therefore, Option B is correct.