Biomolecules & Enzymes — Biology

Q.1

WBCS Prelims 2022

Fermentation ability of Yeast is due to

A. Amylase

B. Zymase

C. Invertase

D. Galactase

Explanation

Why Correct: Zymase is the enzyme complex in yeast that catalyzes alcoholic fermentation, converting glucose into ethanol and carbon dioxide.
Distractor Analysis: Amylase breaks down starch into sugars. Invertase hydrolyzes sucrose into glucose and fructose. Galactase is not a recognized enzyme; galactosidase enzymes break down galactose-containing compounds.
Takeaway: Yeast fermentation produces ethanol and CO2, not lactic acid like in muscle cells.

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Q.2

WBCS Prelims 2011

The number of amino acids occurring in nature is

A. 10

B. 20

C. 30

D. 40

Explanation

Why Correct: William Cumming Rose's 1935 research conclusively established 20 standard amino acids as the building blocks of proteins in all living organisms, encoded by the universal genetic code.
Distractor Analysis: 10 represents an incomplete subset of the standard amino acids. 30 includes some rare modified amino acids like selenocysteine and pyrrolysine that occur in specific contexts but aren't part of the universal set. 40 approximates the total count of known naturally occurring amino acids including non-proteinogenic ones like ornithine, citrulline, and beta-alanine.
Takeaway: Selenocysteine, incorporated via UGA codon recoding, functions as the 21st proteinogenic amino acid in specific enzymes like glutathione peroxidase and thioredoxin reductase.

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Q.3

WBCS Prelims 2010

Enzymes speed up biochemical reactions by

A. Increasing the activation energy of the reaction

B. Lowering the temperature of the reaction

C. Increasing the temperature of the reaction

D. Lowering the activation energy of the reaction

Explanation

Why Correct: Enzymes function as biological catalysts by providing an alternative reaction pathway with a lower activation energy barrier, allowing more reactant molecules to overcome it per unit time.
Distractor Analysis: Increasing activation energy would slow down the reaction. Lowering temperature generally decreases reaction rates by reducing molecular kinetic energy. Increasing temperature can speed up reactions but is not the mechanism of enzyme catalysis and can denature enzymes.
Takeaway: Enzymes do not alter the equilibrium constant or the free energy change (ΔG) of a reaction—they only accelerate the rate at which equilibrium is reached.

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Q.4

WBCS Prelims 2009

Which of the following vitamins forms the prosthetic group of acyl-COA dehydrogenase ?

A. Nicotinic acid

B. Pyridoxine

C. Pantothenic acid

D. Riboflavin

Explanation

Why Correct: Riboflavin (vitamin B2) forms FAD (flavin adenine dinucleotide), which serves as the prosthetic group for acyl-CoA dehydrogenase in fatty acid beta-oxidation.
Distractor Analysis: Nicotinic acid (niacin) forms NAD+/NADP+ coenzymes. Pyridoxine (vitamin B6) forms pyridoxal phosphate for transamination. Pantothenic acid forms coenzyme A, which carries acyl groups but is not the prosthetic group of acyl-CoA dehydrogenase.
Takeaway: FAD-dependent dehydrogenases include succinate dehydrogenase (Krebs cycle) and glycerol-3-phosphate dehydrogenase (electron transport shuttle).

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Q.5

WBCS Prelims 2008

The biochemical processes taking place in the body is known as

A. Anabolism

B. Catabolism

C. Metabolism

D. None of the above

Explanation

Why Correct: Metabolism encompasses all biochemical reactions in living organisms, including both anabolic (building) and catabolic (breaking down) processes that maintain life.
Distractor Analysis: Anabolism specifically refers to synthesis reactions that build complex molecules from simpler ones, catabolism describes breakdown reactions that release energy from complex molecules, and 'None of the above' is incorrect since metabolism accurately defines the complete set of biochemical processes.
Takeaway: Basal metabolic rate measures energy expenditure at complete rest, while metabolic pathways like glycolysis and Krebs cycle are specific sequences of biochemical reactions.

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Q.6

WBCS Prelims 2005

Cholesterol is a/an

A. Saturated fat

B. Unsaturated fat

C. Steroid

D. Diglyceride

Explanation

Why Correct: Cholesterol is a steroid alcohol with a characteristic four-ring hydrocarbon structure and a hydroxyl group, classified as a sterol.
Distractor Analysis: Saturated fats contain only single bonds between carbon atoms, like butter and lard. Unsaturated fats have one or more double bonds, like olive oil and fish oil. Diglycerides consist of two fatty acids attached to a glycerol backbone.
Takeaway: All steroids share the same four-ring structure, including hormones like testosterone and cortisol.

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Q.7

WBCS Prelims 2013

Which metal ion is associated with Haemoglobin?

A. Mg++

B. Fe++

C. Al+++

D. Mn++

Explanation

Why Correct: Haemoglobin contains iron(II) ions (Fe2+) at the center of each heme group, which bind oxygen molecules for transport in red blood cells.
Distractor Analysis: Magnesium ions (Mg2+) are essential for chlorophyll in plants and many enzyme cofactors. Aluminum ions (Al3+) are not biologically significant in human physiology and are toxic in excess. Manganese ions (Mn2+) serve as cofactors for some enzymes like superoxide dismutase but are not part of haemoglobin.
Takeaway: Chlorophyll contains magnesium, while vitamin B12 contains cobalt—both are common exam contrasts with haemoglobin's iron.

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Q.8

WBCS Prelims 2012

Proteins are detected by

A. Molish’s test

B. Biuret test

C. DNP test

D. Benedict’s test

Explanation

Why Correct: Biuret test uses alkaline copper sulfate to form violet complex with peptide bonds, specifically detecting proteins and peptides with at least two peptide bonds.
Distractor Analysis: Molish's test identifies carbohydrates via alpha-naphthol reaction, DNP test detects amino groups in amino acids, and Benedict's test reduces copper(II) to copper(I) oxide for reducing sugars.
Takeaway: Ninhydrin test detects amino acids and proteins with free amino groups, producing purple color, while xanthoproteic test identifies aromatic amino acids through nitration.

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Q.9

WBPSC Miscellaneous Prelims 2012

Haemoglobin is

A. a copper compound

B. a cobalt compound

C. a magnesium compound

D. an iron compound

Explanation

Why Correct: Haemoglobin is a metalloprotein containing iron (Fe2+) at the centre of each heme group, enabling oxygen binding and transport.
Distractor Analysis: Copper is found in haemocyanin (in some arthropods and molluscs), not in human haemoglobin. Cobalt is central to vitamin B12 (cobalamin), not haemoglobin. Magnesium is a key component of chlorophyll in plants, not haemoglobin.
Takeaway: The metal in haemoglobin is iron; in chlorophyll it is magnesium; in haemocyanin it is copper. This comparison is frequently tested in exams.

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Q.10

WBPSC Miscellaneous Prelims 2012

Enzymes are organic compounds of protein category which

A. act as catalysts in life processes

B. help in the mechanism of supply of oxygen in blood

C. help to regulate the manner and rate of use of glucose in body

D. help in heredity maintenance

Explanation

Why Correct: Enzymes are biological catalysts, primarily proteins, that accelerate chemical reactions in living organisms without being consumed. They lower activation energy for metabolic processes.
Distractor Analysis: Option B describes hemoglobin's role in oxygen transport, not an enzyme function. Option C involves insulin regulation of glucose metabolism, which is hormonal, not enzymatic. Option D refers to DNA and hereditary molecules, which are nucleic acids, not enzymes.
Takeaway: The defining function of enzymes is catalysis. Every biology student should know that enzymes are protein catalysts (though some RNA enzymes exist, the classic definition focuses on proteins).

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Q.11

WBPSC Miscellaneous Prelims 2009

Which of the following is not a Pyrimidine base?

A. Thymine

B. Uracil

C. Guanine

D. Cytosine

Explanation

Why Correct: Pyrimidine bases are single-ring structures: cytosine, thymine (DNA), and uracil (RNA). Guanine is a purine base with a double-ring structure, not a pyrimidine.
Distractor Analysis: Thymine, uracil, and cytosine are all pyrimidines. Thymine is found in DNA, uracil replaces thymine in RNA. Guanine pairs with cytosine via three hydrogen bonds but belongs to the purine group alongside adenine.
Takeaway: Purines: Adenine (A) and Guanine (G). Pyrimidines: Cytosine (C), Thymine (T), Uracil (U). Mnemonic: Pure As Gold (Purines: A, G); Pyrimidines: CUT (C, U, T).

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Q.12

WBCS prelims 2024

The most abundant enzyme in the living world is

A. Lipase

B. DNase

C. Zymase

D. Rubisco

Explanation

Why Correct: Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the first major step of carbon fixation in the Calvin cycle, attaching CO2 to RuBP. Because it occurs in all photosynthetic plants, algae, and many bacteria, its total mass exceeds that of any other enzyme.
Distractor Analysis: Lipase breaks down fats into glycerol and fatty acids; it is not globally abundant. DNase degrades DNA molecules; it is not the most abundant. Zymase is a complex of enzymes in yeast that ferments sugars into ethanol and CO2; it is not the most abundant.
Takeaway: Rubisco is also one of the slowest enzymes, fixing only about 3-10 molecules of CO2 per second, which is why plants must produce it in such large quantities.

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