Biomolecules

34 solved questions from Class 12 Chemistry, each with the full working. Tap any question to see the step-by-step solution.

• 1 What is the primary chemical reaction or bonding mechanism highlighted in 'Biomolecules' (Class 12)? medium MCQ Reaction Mechanism & Bonding
• 2 What factor affects the rate or equilibrium constant of reactions in 'Biomolecules'? medium MCQ Chemical Kinetics & Factors
• 3 Which functional group or IUPAC nomenclature rule applies to compounds in 'Biomolecules'? medium MCQ IUPAC Nomenclature & Structure
• 4 What is the major product obtained in the characteristic reaction of 'Biomolecules'? medium MCQ Reaction Products & Selectivity
• 5 At 0 °C, glycine (NH₂CH₂COOH) is treated with excess nitrous acid (HNO₂). What gas is evolved? easy MCQ 3 marks Primary amine oxidation to N₂ gas
• 6 During DNA replication, a DNA polymerase synthesises a complementary strand. If the template strand contains 30 nucleotides, how many phosphodiester bonds are formed in the new strand? medium 4 marks Phosphodiester bond formation in nucleic acids
• 7 A 200 g sample of soybean oil contains 20 % triglycerides. When it is heated at 200 °C for 2 h, 15 % of the triglycerides hydrolyze to free fatty acids. How many grams of free fatty acids are formed? medium 4 marks Triglyceride hydrolysis to free fatty acids
• 8 Insulin is a polypeptide hormone consisting of two chains A and B linked by two inter‑chain disulfide bonds and one intra‑chain bond in the A chain. Explain how reduction of these disulfide bonds affects insulin’s ability to bind to its receptor. Include a brief description of the structural consequence and the functional outcome. hard 5 marks Disulfide bridges stabilize protein folding
• 9 A short DNA segment has the template strand sequence 5'-ATGCCGTA-3'. How many hydrogen bonds are formed between this template strand and its newly synthesized complementary strand? medium 2 marks Base‑pair hydrogen bonding
• 10 Which of the following monosaccharides will give a positive result with Benedict's test (formation of a brick‑red precipitate) at neutral pH? easy MCQ 1 mark Reducing sugars
• 11 A 5.00 g sample of a pure triglyceride (molecular formula C₅₅H₁₀₄O₆) is completely saponified with excess NaOH. The reaction consumes 0.250 mol of NaOH. Calculate the saponification value of the fat in mg KOH g⁻¹. medium 2 marks Saponification value calculation
• 12 Explain how heating the enzyme amylase to 80 °C denatures it and affects its catalytic activity. In your answer, describe (i) the type of structural changes that occur in the protein, (ii) the effect on the geometry of the active site, and (iii) the resulting change in the rate of starch hydrolysis, providing a brief mechanistic rationale. hard 4 marks Protein denaturation and enzyme activity
• 13 A polypeptide chain contains 12 amino acids. If the average molecular weight of an amino acid residue is 110 Da, what is the approximate molecular weight of the chain? medium 2 marks Molecular weight of polypeptide
• 14 In a PCR reaction, primers of 20 bases anneal to the template strand. If 10 of the primer bases are A or T and the remaining 10 are G or C, how many hydrogen bonds are formed between primer and template during annealing? hard MCQ 4 marks Hydrogen bonding in DNA primers
• 15 Which monosaccharide gives a positive Benedict’s test (brick‑red precipitate) at neutral pH? easy MCQ 1 mark Reducing sugars in Benedict’s test
• 16 A 10.0 g sample of triglyceride C_57H_104O_6 is completely saponified with excess NaOH; the reaction consumes 0.375 mol of NaOH. Calculate the saponification value (mg KOH g⁻¹). hard 4 marks Saponification value calculation
• 17 A 4.00 g sample of triglyceride C_55H_104O_6 is completely saponified with excess NaOH. The reaction consumes 0.300 mol of NaOH. Calculate the saponification value (mg KOH g⁻¹). medium 4 marks Calculating saponification value of a fat
• 18 Explain how the reduction of disulfide bonds in insulin affects its three‑dimensional structure and its ability to bind to the insulin receptor, describing the structural changes and functional outcome. hard 5 marks Effect of disulfide bond reduction on protein structure
• 19 A sample of a monosaccharide gives a brick‑red precipitate in Benedict test at neutral pH. Which of the following is the most likely structure of the sugar? easy MCQ 3 marks Identifying reducing sugars at neutral pH
• 20 A 200 g sample of soybean oil contains 25 % triglycerides. When it is heated at 200 °C for 3 h, 18 % of the triglycerides hydrolyze to free fatty acids. How many grams of free fatty acids are formed? medium 4 marks Hydrolysis of triglycerides into free fatty acids
• 21 A primer of 25 bases contains 8 adenine/thyminine (A/T) bases and 17 guanine/cytosine (G/C) bases. How many hydrogen bonds are formed between the primer and its template strand during annealing? easy MCQ 1 mark Base‑pair hydrogen bonding in nucleic acids
• 22 A 2.00 g sample of a triglyceride with molecular formula C55H104O6 is completely saponified with excess NaOH. The amount of KOH equivalent required to neutralise the liberated fatty acids is 0.00680 mol. Calculate the saponification value in mg KOH per gram of fat. medium 3 marks Saponification value of a fat
• 23 Lysozyme contains several intra‑chain disulfide bonds that stabilize its three‑dimensional structure. Explain how reduction of these disulfide bonds by a reducing agent such as dithiothreitol (DTT) affects lysozyme’s structure and its ability to hydrolyse bacterial cell‑wall peptidoglycan. hard 5 marks Disulfide bond reduction and protein activity
• 24 Which of the following monosaccharides will give a brick‑red precipitate in Benedict’s test when the test is performed in alkaline medium? easy MCQ 1 mark Reducing sugars in carbohydrate tests
• 25 A DNA segment has the sequence 5'-G A A T T C G C-3'. When it pairs with its complementary strand, how many hydrogen bonds are formed in total between the two strands? medium 2 marks Hydrogen bonding in DNA base pairing
• 26 Explain how the reduction of disulfide bonds in insulin affects its three‑dimensional structure and its ability to bind to the insulin receptor, describing the structural changes and functional outcome. hard 3 marks Effect of disulfide reduction on protein function
• 27 A primer of 15 bases contains 5 adenine/thyminine (A/T) bases and 10 guanine/cytosine (G/C) bases. How many hydrogen bonds are formed between the primer and its template strand during annealing? medium 1 mark DNA base pairing hydrogen bonds
• 28 Which of the following monosaccharides will give a brick‑red precipitate in Benedict’s test when the test is performed in alkaline medium? (a) D-fructose (b) D-sorbitol (c) D-mannose (d) D-glucitol medium MCQ 1 mark Benedict’s test for reducing sugars
• 29 A 3.00 g sample of a triglyceride with molecular formula C_52H_98O_6 is completely saponified with excess NaOH; the reaction consumes 0.180 mol of NaOH. Calculate the saponification value in mg KOH per gram of fat. easy 2 marks Saponification value calculation
• 30 Which of the following is not a lipid? easy MCQ 1 mark Classification of biomolecules
• 31 Explain how a change in pH from the physiological pH 7.4 to pH 3.0 can affect the tertiary structure of the enzyme amylase and consequently its catalytic activity. In your answer discuss (i) the nature of ionic interactions in the protein, (ii) the impact on the active‑site geometry, and (iii) the overall effect on the reaction rate. hard 3 marks Effect of pH on protein tertiary structure
• 32 A double‑stranded DNA fragment has the sequence 5'-AGCTTAGG-3' on one strand. hard 3 marks Molecular weight & H‑bonding in nucleic acids
• 33 A 0.500 g sample of a polysaccharide is completely hydrolysed with acid to give 0.00012 mol of glucose. Calculate the average degree of polymerisation (DP) of the polysaccharide. medium 2 marks Degree of polymerisation
• 34 Which of the following is not a carbohydrate? (a) Glucose (b) Cellulose (c) Sucrose (d) Lysozyme easy MCQ 3 marks Classification of biomolecules