Biomolecules (Class 12 NCERT) Revision Notes

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Biomolecules

112 Short Q&A • NCERT Class 12 Chemistry

Class 12 JEE / NEET

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112 Short Q&A for Biomolecules

Part 1: Carbohydrates (Structure and Classification)
1. Q1: Define Carbohydrates chemically.
   A: Polyhydroxy aldehydes or ketones, or compounds that produce them on hydrolysis.
2. Q2: What is the general formula of most carbohydrates?
   A: C_x(H₂O)_y (hydrates of carbon).
3. Q3: What are Saccharides?
   A: The common term for carbohydrates (from Latin saccharum = sugar).
4. Q4: How are carbohydrates classified based on hydrolysis products?
   A: Monosaccharides, Oligosaccharides, and Polysaccharides.
5. Q5: Define Monosaccharide.
   A: The simplest carbohydrate that cannot be hydrolyzed further (e.g., Glucose).
6. Q6: Define Oligosaccharide.
   A: Carbohydrates that yield 2 to 10 monosaccharide units upon hydrolysis.
7. Q7: Define Polysaccharide.
   A: Carbohydrates that yield a large number of monosaccharide units upon hydrolysis.
8. Q8: Give two examples of monosaccharides.
   A: Glucose and Fructose.
9. Q9: Give two examples of disaccharides.
   A: Sucrose and Lactose.
10. Q10: Give two examples of polysaccharides.
    A: Starch and Cellulose.
11. Q11: What are Reducing Sugars?
    A: Carbohydrates that reduce Tollen's reagent or Fehling's solution (e.g., Glucose, Fructose, Maltose).
12. Q12: Which sugar is a non-reducing sugar?
    A: Sucrose.
13. Q13: What is the functional group of Aldoses?
    A: Aldehyde (-CHO).
14. Q14: What is the functional group of Ketoses?
    A: Ketone (C=O).
15. Q15: What is the term for a monosaccharide with 6 carbons?
    A: Hexose (e.g., Glucose, Fructose).
16. Q16: What is the main structural difference between α-D-Glucose and β-D-Glucose?
    A: The configuration of the OH group at the C-1 anomeric carbon.
17. Q17: What are Anomers?
    A: Stereoisomers of cyclic carbohydrates that differ only in configuration at the C-1 (anomeric) carbon.
18. Q18: What is Mutarotation?
    A: The spontaneous change in the optical rotation of an optically active sugar solution until an equilibrium mixture of α and β forms is reached.
Part 2: Glucose and Glycosidic Linkage
19. Q19: What is the open-chain formula of Glucose?
    A: CHO(CHOH)₄CH₂OH (an aldohexose).
20. Q20: Why is the open-chain structure of glucose insufficient?
    A: It doesn't explain mutarotation, the α/β forms, or the lack of reaction with NaHSO₃.
21. Q21: What reaction confirms the presence of five OH groups in glucose?
    A: Reaction with Acetic Anhydride to form penta-acetate.
22. Q22: What is the D and L configuration in monosaccharides based on?
    A: The configuration of the OH group on the penultimate carbon (C-5 in glucose).
23. Q23: What is the ring structure of glucose commonly called?
    A: Pyranose ring (six-membered ring).
24. Q24: What is the ring structure of fructose commonly called?
    A: Furanose ring (five-membered ring).
25. Q25: What is a Glycosidic Linkage?
    A: The ether linkage (-O-) formed when two monosaccharide units condense with the loss of a water molecule.
26. Q26: What is the composition of Sucrose?
    A: α-D-Glucose and β-D-Fructose.
27. Q27: What is the composition of Maltose?
    A: Two α-D-Glucose units.
28. Q28: What is the composition of Lactose?
    A: β-D-Galactose and β-D-Glucose.
29. Q29: What is Invert Sugar?
    A: The equimolar mixture of D-Glucose and D-Fructose obtained after the hydrolysis of sucrose.
30. Q30: What is the bond type in Cellulose?
    A: β-Glycosidic linkages (C-1 of one glucose to C-4 of the next).
31. Q31: What are the two components of Starch?
    A: Amylose (linear) and Amylopectin (branched).
32. Q32: What is Glycogen?
    A: The storage polysaccharide in animals (similar to amylopectin but more highly branched).
Part 3: Proteins (Amino Acids and Structure)
33. Q33: What are Proteins?
    A: Polymers of α-Amino Acids linked by peptide bonds.
34. Q34: What two functional groups define an α-Amino Acid?
    A: Amino group (-NH₂) and Carboxyl group (-COOH).
35. Q35: Why are α-amino acids naturally preferred over β or γ?
    A: Both functional groups are attached to the same (α) carbon atom.
36. Q36: What is the simplest amino acid?
    A: Glycine (R=H).
37. Q37: Why is Glycine optically inactive?
    A: It lacks a chiral α-carbon (has two H atoms attached).
38. Q38: What is a Zwitter Ion (or Dipolar Ion)?
    A: An amino acid structure that contains both a positive (-NH₃⁺) and a negative (-COO^-) charge.
39. Q39: Define Isoelectric Point (pI).
    A: The pH at which the amino acid exists as a neutral Zwitter ion and does not migrate in an electric field.
40. Q40: What is a Peptide Bond?
    A: The amide linkage (-CONH-) formed by the reaction between the -COOH group of one amino acid and the -NH₂ group of another.
41. Q41: Define a Dipeptide.
    A: A molecule formed by two amino acids joined by one peptide bond.
42. Q42: What are the two main classes of proteins based on their shape?
    A: Fibrous and Globular.
43. Q43: Give an example of a Fibrous Protein.
    A: Keratin (hair, nails) or Myosin (muscles).
44. Q44: Give an example of a Globular Protein.
    A: Insulin or Albumin (enzymes and hormones).
45. Q45: Define the Primary Structure of a protein.
    A: The specific sequence in which amino acids are linked in a polypeptide chain.
46. Q46: Define the Secondary Structure of a protein.
    A: The coiling or folding of the polypeptide chain (α-helix or β-pleated sheet).
47. Q47: What bonds stabilize the Secondary Structure?
    A: Hydrogen Bonds between the -NH and C=O groups.
48. Q48: Define Denaturation of a protein.
    A: The process where the 2°, 3°, and 4° structures are disrupted, leading to the loss of biological activity.
49. Q49: Does the Primary Structure change during denaturation?
    A: No.
50. Q50: Give two common causes of protein denaturation.
    A: Change in temperature or change in pH.
Part 4: Nucleic Acids (DNA and RNA)
51. Q51: What are the two main types of nucleic acids?
    A: Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA).
52. Q52: What is the function of DNA?
    A: Storage and transfer of genetic information; blueprint for protein synthesis.
53. Q53: What is the function of RNA?
    A: Protein synthesis (transfer, messenger, ribosomal RNA).
54. Q54: What are the three chemically distinct components of a Nucleotide?
    A: Pentose Sugar, Nitrogenous Base, and Phosphate Group.
55. Q55: What sugar is present in DNA?
    A: β-D-2-deoxyribose.
56. Q56: What sugar is present in RNA?
    A: β-D-ribose.
57. Q57: Name the two classes of nitrogenous bases.
    A: Purines (two rings) and Pyrimidines (one ring).
58. Q58: Name the four bases present in DNA.
    A: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
59. Q59: Name the four bases present in RNA.
    A: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U).
60. Q60: What is the difference between a Nucleoside and a Nucleotide?
    A: Nucleoside = Sugar + Base; Nucleotide = Sugar + Base + Phosphate.
61. Q61: What is the chemical linkage that joins the phosphate group and the sugar in a nucleic acid chain?
    A: Phosphodiester Linkage.
62. Q62: State Chargaff's Rule for DNA.
    A: The amount of Adenine equals Thymine (A=T) and Guanine equals Cytosine (G=C).
63. Q63: What are the two types of bonds that hold the two strands of the DNA double helix together?
    A: Hydrogen Bonds between complementary base pairs.
64. Q64: What base pairing occurs between A and T?
    A: Two Hydrogen Bonds.
65. Q65: What base pairing occurs between G and C?
    A: Three Hydrogen Bonds.
66. Q66: What is the main structural difference between DNA and RNA?
    A: DNA is double-stranded; RNA is mostly single-stranded.
67. Q67: What is the term for the process of DNA synthesizing its own exact copy?
    A: Replication.
Part 5: Enzymes and Hormones
68. Q68: What are Enzymes?
    A: Biological catalysts that speed up biochemical reactions in living systems.
69. Q69: What is the chemical nature of most enzymes?
    A: Globular Proteins.
70. Q70: What is the primary characteristic of enzyme action?
    A: They are highly specific to a particular substrate or reaction.
71. Q71: What model explains the specific binding of an enzyme to its substrate?
    A: Lock and Key Model.
72. Q72: What is the optimum pH for enzyme activity?
    A: Usually around pH 7 (physiological pH).
73. Q73: What is the effect of high temperature on enzyme activity?
    A: Denaturation (loss of activity).
74. Q74: What are Hormones?
    A: Chemical messengers secreted by endocrine glands directly into the bloodstream.
75. Q75: Give two examples of protein-based hormones.
    A: Insulin and Glucagon.
76. Q76: Give two examples of steroid-based hormones.
    A: Estrogen and Testosterone.
77. Q77: What is the function of Insulin?
    A: Regulates blood sugar levels (lowers glucose concentration).
78. Q78: What is the primary cause of Diabetes Mellitus?
    A: Insulin deficiency or resistance.
Part 6: Vitamins
79. Q79: What are Vitamins?
    A: Organic compounds required in the diet in small amounts to perform specific biological functions for growth and health.
80. Q80: How are vitamins classified based on solubility?
    A: Fat-soluble and Water-soluble.
81. Q81: Name the four Fat-Soluble vitamins.
    A: A, D, E, K.
82. Q82: Name two Water-Soluble vitamins.
    A: B-group vitamins and Vitamin C.
83. Q83: What is the chemical name for Vitamin A?
    A: Retinol.
84. Q84: What deficiency disease is caused by a lack of Vitamin A?
    A: Night Blindness (Xerophthalmia).
85. Q85: What is the chemical name for Vitamin C?
    A: Ascorbic Acid.
86. Q86: What deficiency disease is caused by a lack of Vitamin C?
    A: Scurvy.
87. Q87: What is the chemical name for Vitamin D?
    A: Calciferol.
88. Q88: What deficiency disease is caused by a lack of Vitamin D?
    A: Rickets (in children) or Osteomalacia (in adults).
89. Q89: What is the chemical name for Vitamin E?
    A: Tocopherol.
90. Q90: What is the function of Vitamin K?
    A: Essential for blood clotting (Coagulation).
91. Q91: What is the deficiency disease caused by a lack of Vitamin B₁?
    A: Beri-beri.
92. Q92: Why must water-soluble vitamins be supplied regularly in the diet?
    A: They are excreted in the urine and cannot be stored in the body.
Part 7: Miscellaneous Concepts
93. Q93: What is the term for the storage of excess glucose in the liver and muscles?
    A: Glycogenesis (forming Glycogen).
94. Q94: What is the linkage between the two monosaccharides in Sucrose?
    A: α,β-glycosidic linkage (between C-1 of α-glucose and C-2 of β-fructose).
95. Q95: What is the type of linkage that connects C-1 to C-4 in Amylose?
    A: α-Glycosidic linkage.
96. Q96: What are the two types of H-bonds in the α-helix structure of proteins?
    A: Intrachain H-bonds (within the same chain).
97. Q97: What is the primary use of RNA interference (RNAi)?
    A: Gene silencing (switching off specific genes).
98. Q98: Why are all amino acids (except glycine) optically active?
    A: They have a chiral α-carbon (four different groups attached).
99. Q99: What is the essential difference between the sugar in a DNA and an RNA nucleotide?
    A: DNA sugar lacks an OH group at the C-2 position.
100. Q100: What is the primary role of Cholesterol in the human body?
     A: Precursor for the synthesis of steroid hormones and Vitamin D.
101. Q101: What is the product of the hydrolysis of proteins?
     A: α-Amino Acids.
102. Q102: What is the product of the hydrolysis of Starch?
     A: D-Glucose.
103. Q103: What is the relationship between the pI and the net charge of an amino acid at pH<pI?
     A: The amino acid has a net positive charge (NH₃⁺ dominates).
104. Q104: What is the relationship between the pI and the net charge of an amino acid at pH>pI?
     A: The amino acid has a net negative charge (COO^- dominates).
105. Q105: What is a Chromoprotein?
     A: A protein that contains a colored prosthetic group (e.g., Hemoglobin).
106. Q106: What is the full form of ATP?
     A: Adenosine Triphosphate (the energy currency of the cell).
107. Q107: What is the bond that releases a large amount of energy upon hydrolysis in ATP?
     A: Phosphate anhydride bond (high-energy bond).
108. Q108: What is the term for the sequence of three bases on tRNA that pairs with the codon on mRNA?
     A: Anticodon.
109. Q109: What is the term for the three-dimensional structure of a single polypeptide chain stabilized by various bonds?
     A: Tertiary Structure.
110. Q110: What is the main structural feature of the β-pleated sheet?
     A: Lateral H-bonding between adjacent polypeptide chains.
111. Q111: Why is the DNA molecule acidic?
     A: Due to the presence of Phosphate Groups (H₃PO₄ backbone).
112. Q112: What is the name of the bond that links the base to the sugar in a nucleoside?
     A: N-glycosidic linkage (C-1 of sugar to N-1 or N-9 of base).

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