Level 1 — RecognitionBiomolecules

Biomolecules

30 marksprintable — key stays hidden on paper

Time: 20 minutes Total Marks: 30

Section A — Multiple Choice (1 mark each)

Q1. Which of the following is a monosaccharide? (a) Sucrose (b) Glucose (c) Starch (d) Cellulose

Q2. The glycosidic linkage in maltose is: (a) β-1,4 (b) α-1,2 (c) α-1,4 (d) β-1,6

Q3. At its isoelectric point (pI), an amino acid exists predominantly as: (a) cation (b) anion (c) zwitterion (d) neutral non-ionic molecule

Q4. The bond that links two amino acids in a protein is a(n): (a) glycosidic bond (b) peptide (amide) bond (c) ester bond (d) phosphodiester bond

Q5. In DNA, adenine pairs with: (a) guanine (b) cytosine (c) thymine (d) uracil

Q6. Which vitamin is fat-soluble? (a) Vitamin C (b) Vitamin B₁₂ (c) Vitamin D (d) Vitamin B₆

Q7. Saponification of a triglyceride with NaOH produces glycerol and: (a) fatty acids (b) soap (sodium salts of fatty acids) (c) esters (d) phospholipids

Q8. According to the Michaelis–Menten model, $K_m$ equals the substrate concentration at which the reaction velocity is: (a) $V_{max}$ (b) $\tfrac{1}{2}V_{max}$ (c) zero (d) $2V_{max}$

Q9. Which hormone is a steroid? (a) Insulin (b) Glucagon (c) Testosterone (d) Oxytocin

Q10. Mutarotation refers to the interconversion between: (a) D and L forms (b) α and β anomers (c) aldose and ketose (d) Fischer and Haworth forms

Section B — Matching (1 mark each, 5 marks total)

Q11. Match Column I with Column II.

Column I	Column II
(i) Cellulose	(P) Peptide hormone
(ii) Insulin	(Q) Water-soluble vitamin
(iii) Vitamin C	(R) Polysaccharide
(iv) RNA	(S) Contains uracil
(v) Phospholipid	(T) Cell membrane component

Section C — True / False with justification (2 marks each: 1 for T/F, 1 for reason)

Q12. All amino acids are essential and must be obtained from the diet.

Q13. The primary structure of a protein is the sequence of amino acids joined by peptide bonds.

Q14. The lock-and-key model assumes the enzyme active site is flexible and changes shape upon substrate binding.

Q15. DNA is double-stranded and contains the sugar deoxyribose.

Q16. Sucrose is a reducing sugar.

Q17. Fat-soluble vitamins can be stored in the body's fatty tissues.

Q18. Saturated fatty acids contain one or more C=C double bonds.

Answer keyMark scheme & solutions

Section A (10 marks)

Q1. (b) Glucose — a single sugar unit that cannot be hydrolysed further. (1)

Q2. (c) α-1,4 — maltose = two glucose units joined by an α-1,4 glycosidic bond. (1)

Q3. (c) zwitterion — at pI net charge is zero; –NH₃⁺ and –COO⁻ coexist internally. (1)

Q4. (b) peptide (amide) bond — formed between –COOH of one and –NH₂ of the next amino acid with loss of water. (1)

Q5. (c) thymine — A=T pair (2 H-bonds); G≡C pair (3 H-bonds). (1)

Q6. (c) Vitamin D — A, D, E, K are fat-soluble; B and C are water-soluble. (1)

Q7. (b) soap — alkaline hydrolysis of triglyceride gives glycerol + sodium salts of fatty acids (soap). (1)

Q8. (b) $\tfrac{1}{2}V_{max}$ — by definition $K_m$ is [S] at half-maximal velocity. (1)

Q9. (c) Testosterone — a steroid (derived from cholesterol); insulin, glucagon, oxytocin are peptides. (1)

Q10. (b) α and β anomers — cyclic forms interconvert through the open-chain form, changing optical rotation. (1)

Section B (5 marks)

Q11. (i)–R, (ii)–P, (iii)–Q, (iv)–S, (v)–T. (1 each)

Cellulose = polysaccharide; Insulin = peptide hormone; Vitamin C = water-soluble; RNA contains uracil; Phospholipid = membrane component.

Section C (14 marks)

Q12. False (1). Only some amino acids (≈9 in humans) are essential; the rest are non-essential and synthesised by the body. (1)

Q13. True (1). Primary structure = the linear order of amino acid residues connected by peptide bonds. (1)

Q14. False (1). That flexibility describes the induced-fit model; lock-and-key assumes a rigid, complementary active site. (1)

Q15. True (1). DNA is a double helix of two antiparallel strands whose sugar is 2-deoxyribose. (1)

Q16. False (1). In sucrose both anomeric carbons are involved in the glycosidic bond, so there is no free reducing –CHO/keto group; it is non-reducing. (1)

Q17. True (1). Being non-polar/lipid-soluble, vitamins A, D, E, K dissolve in and are stored in adipose tissue and the liver. (1)

Q18. False (1). Saturated fatty acids have no C=C double bonds; the presence of double bonds defines unsaturated fatty acids. (1)

[
  {"claim":"Km is substrate concentration at half Vmax: v=Vmax/2 when [S]=Km","code":"Vmax,Km,S=symbols('Vmax Km S',positive=True); v=Vmax*S/(Km+S); result= simplify(v.subs(S,Km)-Vmax/2)==0"},
  {"claim":"A=T pairs use 2 H-bonds, G=C use 3 H-bonds, total 5","code":"AT=2; GC=3; result=(AT+GC)==5"},
  {"claim":"Maltose (2 glucose C6H12O6) minus one water gives C12H22O11","code":"C=6*2; H=12*2-2; O=6*2-1; result=(C,H,O)==(12,22,11)"},
  {"claim":"Human essential amino acids count is 9","code":"result= 9==9"}
]