Macromolecules MCQs set 2 for ETEA / KMU MDCAT (KPK) Chemistry — 20 solved questions.
Q1. A researcher synthesizes a linear polypeptide consisting of 50 amino acid residues. How many peptide bonds are formed in this specific macromolecule?
Answer: 49 bonds
Explanation: A polypeptide chain contains (n-1) peptide bonds; 50 amino acids minus 1 equals 49. Option D fails by assuming bonds equal the number of monomers.
Q2. During the synthesis of sucrose from glucose and fructose (C6H12O6 each), one molecule of water is eliminated. What is the resulting molecular mass of sucrose?
Answer: 342 amu
Explanation: The formula for a disaccharide is 2(C6H12O6) minus H2O, resulting in 342 amu. Option A is the weight of two separate hexoses without dehydration.
Q3. A sample of Polyvinyl Chloride (PVC) has an average molecular mass of 62,500 amu. Calculate the degree of polymerization for this polymer sample.
Answer: 1000
Explanation: Degree of polymerization is calculated by dividing polymer mass (62,500) by vinyl chloride monomer mass (62.5). Option B incorrectly uses the ethylene mass.
Q4. A chemist performs the saponification of 1 mole of glyceryl tristearate (a triglyceride). How many moles of potassium hydroxide (KOH) are required for complete hydrolysis?
Answer: 3 moles
Explanation: One mole of triglyceride requires three moles of KOH for complete saponification. Option A reflects a 1:1 ratio, which only applies to simple carboxylic acids.
Q5. A plant cell produces a linear starch chain by condensing 100 glucose molecules. How many molecules of water are released during this polymerization process?
Answer: 99 molecules
Explanation: In a linear polysaccharide of 100 units, 99 water molecules are released (n-1). Option B incorrectly assumes one water molecule per glucose unit.
Q6. Analysis of a double-stranded DNA sample shows that Adenine makes up 20% of the nitrogenous bases. What is the percentage of Guanine in this sample?
Answer: 30%
Explanation: According to Chargaff's rule, A=T (20%) and G=C. Since A+T=40%, G+C must be 60%, making G equal to 30%. Option B is the percentage of Thymine.
Q7. An artificial sweetener is a pentapeptide synthesized in a lab. How many water molecules were eliminated to form the peptide linkages in this molecule?
Answer: 4 water molecules
Explanation: A pentapeptide contains five amino acids linked by four peptide bonds. Option C is tempting but describes the number of amino acids, not the bonds.
Q8. In the fermentation of 180g of glucose by yeast enzymes, what is the total mass of carbon dioxide gas evolved at STP?
Answer: 88 g
Explanation: Fermentation of 1 mole (180g) of glucose produces 2 moles of CO2 (88g). Option A is the mass of only one mole of carbon dioxide.
Q9. A nutritionist calculates the protein content of a food sample based on its nitrogen mass. What is the average percentage of nitrogen in proteins?
Answer: 16%
Explanation: Proteins typically contain approximately 16% nitrogen by mass. Option B is a common distractor but represents the percentage of other elements like hydrogen.
Q10. An organic chemist examines the open-chain structural formula of D-glucose. How many asymmetric (chiral) carbon atoms are present in this single molecule?
Answer: 4
Explanation: Glucose (C6H12O6) has 4 chiral centers in its open-chain form. Option D refers to the cyclic alpha/beta forms which have 5 chiral centers.
Q11. Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene). If a rubber molecule has a mass of 68,000 amu, how many isoprene units are present?
Answer: 1000
Explanation: Isoprene (C5H8) has a mass of 68. Dividing 68,000 by 68 gives 1000 units. Option A incorrectly uses the mass of a saturated pentane unit.
Q12. A lipid molecule of tripalmitin undergoes complete enzymatic hydrolysis in the small intestine. How many molecules of glycerol are produced per molecule of tripalmitin?
Answer: 1 molecule
Explanation: Triglycerides consist of one glycerol molecule and three fatty acids. Option B is incorrect because glycerol is a triol, not a triple molecule.
Q13. In the industrial production of Nylon-6,6, what is the required molar ratio of adipic acid to hexamethylenediamine to ensure a high molecular weight polymer?
Answer: 1:1
Explanation: Nylon-6,6 is formed from adipic acid and hexamethylenediamine in a 1:1 molar ratio. Option D is incorrect as it implies a different polymer type.
Q14. Amylose is a linear polysaccharide. If a specific amylose chain consists of 50 glucose residues, how many alpha-1,4-glycosidic linkages are present in the molecule?
Answer: 49
Explanation: A linear chain of 50 glucose units contains 49 glycosidic linkages (n-1). Option A fails by including the terminal hydroxyls as linkages.
Q15. What is the molecular mass of Glycine, the simplest amino acid, given its formula H2N-CH2-COOH and the atomic masses C=12, O=16, N=14, H=1?
Answer: 75 amu
Explanation: Glycine (H2N-CH2-COOH) has a molecular weight of 75. Option B is the mass of Alanine, which has an extra methyl group.
Q16. An unknown amino acid has a molecular mass of 117 amu. If the general backbone (H2N-CH-COOH) mass is 74 amu, what is the mass of the R-group?
Answer: 43 amu
Explanation: The mass of the R-group is Total Mass (117) minus the constant amino acid backbone mass (74). Option B incorrectly subtracts only the glycine residue.
Q17. Triolein is a triglyceride containing three oleic acid residues, each with one double bond. How many moles of I2 will react with 1 mole of triolein?
Answer: 3 moles
Explanation: Iodine value measures unsaturation; 1 mole of triolein (3 double bonds) reacts with 3 moles of I2 (6 atoms). Option B ignores the three fatty acid chains.
Q18. During the laboratory synthesis of a tripeptide from three distinct amino acids, how many molecules of water are produced as by-products?
Answer: 2
Explanation: A tripeptide is formed by three amino acids and two peptide bonds. Option A incorrectly counts the amino acids as the bonds.
Q19. Carbonic anhydrase converts 600,000 molecules of CO2 per minute. Calculate the turnover number (molecules per second) for this macromolecular catalyst.
Answer: 10,000
Explanation: Turnover number is molecules converted per second (600,000 / 60 = 10,000). Option A is the per-minute rate given in the question.
Q20. A laboratory technician heats an egg white solution, causing it to coagulate and become insoluble. Which process describes this irreversible structural change?
Answer: Denaturation
Explanation: Proteins denature when heat disrupts hydrogen bonds and hydrophobic interactions. Renaturation is tempting but rarely occurs for highly complex structures.