Biomolecules (Class 12 NCERT) Revision Notes

 short question-and-answer pairs covering the essential concepts from the NCERT Class 12 Chemistry Chapter

Short Q&A for Biomolecules (Class 12 NCERT)

Part 1: Carbohydrates (Structure and Classification)

Q. No.	Question	Answer
1	Define Carbohydrates chemically.	Polyhydroxy aldehydes or ketones, or compounds that produce them on hydrolysis.
2	What is the general formula of most carbohydrates?	Cx​(H2​O)y​ (hydrates of carbon).
3	What are Saccharides?	The common term for carbohydrates (from Latin saccharum = sugar).
4	How are carbohydrates classified based on hydrolysis products?	Monosaccharides, Oligosaccharides, and Polysaccharides.
5	Define Monosaccharide.	The simplest carbohydrate that cannot be hydrolyzed further (e.g., Glucose).
6	Define Oligosaccharide.	Carbohydrates that yield 2 to 10 monosaccharide units upon hydrolysis.
7	Define Polysaccharide.	Carbohydrates that yield a large number of monosaccharide units upon hydrolysis.
8	Give two examples of monosaccharides.	Glucose and Fructose.
9	Give two examples of disaccharides.	Sucrose and Lactose.
10	Give two examples of polysaccharides.	Starch and Cellulose.
11	What are Reducing Sugars?	Carbohydrates that reduce Tollen's reagent or Fehling's solution (e.g., Glucose, Fructose, Maltose).
12	Which sugar is a non-reducing sugar?	Sucrose.
13	What is the functional group of Aldoses?	Aldehyde (-CHO).
14	What is the functional group of Ketoses?	Ketone (C=O).
15	What is the term for a monosaccharide with 6 carbons?	Hexose (e.g., Glucose, Fructose).
16	What is the main structural difference between α-D-Glucose and β-D-Glucose?	The configuration of the OH group at the C−1 anomeric carbon.
17	What are Anomers?	Stereoisomers of cyclic carbohydrates that differ only in configuration at the C−1 (anomeric) carbon.
18	What is Mutarotation?	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

Q. No.	Question	Answer
19	What is the open-chain formula of Glucose?	CHO(CHOH)4​CH2​OH (an aldohexose).
20	Why is the open-chain structure of glucose insufficient?	It doesn't explain mutarotation, the α/β forms, or the lack of reaction with NaHSO3​.
21	What reaction confirms the presence of five OH groups in glucose?	Reaction with Acetic Anhydride to form penta-acetate.
22	What is the D and L configuration in monosaccharides based on?	The configuration of the OH group on the penultimate carbon (C−5 in glucose).
23	What is the ring structure of glucose commonly called?	Pyranose ring (six-membered ring).
24	What is the ring structure of fructose commonly called?	Furanose ring (five-membered ring).
25	What is a Glycosidic Linkage?	The ether linkage (-O-) formed when two monosaccharide units condense with the loss of a water molecule.
26	What is the composition of Sucrose?	α-D-Glucose and β-D-Fructose.
27	What is the composition of Maltose?	Two α-D-Glucose units.
28	What is the composition of Lactose?	β-D-Galactose and β-D-Glucose.
29	What is Invert Sugar?	The equimolar mixture of D-Glucose and D-Fructose obtained after the hydrolysis of sucrose.
30	What is the bond type in Cellulose?	β-Glycosidic linkages (C−1 of one glucose to C−4 of the next).
31	What are the two components of Starch?	Amylose (linear) and Amylopectin (branched).
32	What is Glycogen?	The storage polysaccharide in animals (similar to amylopectin but more highly branched).

Part 3: Proteins (Amino Acids and Structure)

Q. No.	Question	Answer
33	What are Proteins?	Polymers of α-Amino Acids linked by peptide bonds.
34	What two functional groups define an α-Amino Acid?	Amino group (-NH2​) and Carboxyl group (-COOH).
35	Why are α-amino acids naturally preferred over β or γ?	Both functional groups are attached to the same (α) carbon atom.
36	What is the simplest amino acid?	Glycine (R=H).
37	Why is Glycine optically inactive?	It lacks a chiral α-carbon (has two H atoms attached).
38	What is a Zwitter Ion (or Dipolar Ion)?	An amino acid structure that contains both a positive (-NH3+​) and a negative (-COO−) charge.
39	Define Isoelectric Point (pI).	The pH at which the amino acid exists as a neutral Zwitter ion and does not migrate in an electric field.
40	What is a Peptide Bond?	The amide linkage (-CONH-) formed by the reaction between the -COOH group of one amino acid and the -NH2​ group of another.
41	Define a Dipeptide.	A molecule formed by two amino acids joined by one peptide bond.
42	What are the two main classes of proteins based on their shape?	Fibrous and Globular.
43	Give an example of a Fibrous Protein.	Keratin (hair, nails) or Myosin (muscles).
44	Give an example of a Globular Protein.	Insulin or Albumin (enzymes and hormones).
45	Define the Primary Structure of a protein.	The specific sequence in which amino acids are linked in a polypeptide chain.
46	Define the Secondary Structure of a protein.	The coiling or folding of the polypeptide chain (α-helix or β-pleated sheet).
47	What bonds stabilize the Secondary Structure?	Hydrogen Bonds between the -NH and C=O groups.
48	Define Denaturation of a protein.	The process where the 2∘,3∘, and 4∘ structures are disrupted, leading to the loss of biological activity.
49	Does the Primary Structure change during denaturation?	No.
50	Give two common causes of protein denaturation.	Change in temperature or change in pH.

Part 4: Nucleic Acids (DNA and RNA)

Q. No.	Question	Answer
51	What are the two main types of nucleic acids?	Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA).
52	What is the function of DNA?	Storage and transfer of genetic information; blueprint for protein synthesis.
53	What is the function of RNA?	Protein synthesis (transfer, messenger, ribosomal RNA).
54	What are the three chemically distinct components of a Nucleotide?	Pentose Sugar, Nitrogenous Base, and Phosphate Group.
55	What sugar is present in DNA?	β-D-2-deoxyribose.
56	What sugar is present in RNA?	β-D-ribose.
57	Name the two classes of nitrogenous bases.	Purines (two rings) and Pyrimidines (one ring).
58	Name the four bases present in DNA.	Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
59	Name the four bases present in RNA.	Adenine (A), Guanine (G), Cytosine (C), and Uracil (U).
60	What is the difference between a Nucleoside and a Nucleotide?	Nucleoside = Sugar + Base; Nucleotide = Sugar + Base + Phosphate.
61	What is the chemical linkage that joins the phosphate group and the sugar in a nucleic acid chain?	Phosphodiester Linkage.
62	State Chargaff's Rule for DNA.	The amount of Adenine equals Thymine (A=T) and Guanine equals Cytosine (G=C).
63	What are the two types of bonds that hold the two strands of the DNA double helix together?	Hydrogen Bonds between complementary base pairs.
64	What base pairing occurs between A and T?	Two Hydrogen Bonds.
65	What base pairing occurs between G and C?	Three Hydrogen Bonds.
66	What is the main structural difference between DNA and RNA?	DNA is double-stranded; RNA is mostly single-stranded.
67	What is the term for the process of DNA synthesizing its own exact copy?	Replication.

Part 5: Enzymes and Hormones

Q. No.	Question	Answer
68	What are Enzymes?	Biological catalysts that speed up biochemical reactions in living systems.
69	What is the chemical nature of most enzymes?	Globular Proteins.
70	What is the primary characteristic of enzyme action?	They are highly specific to a particular substrate or reaction.
71	What model explains the specific binding of an enzyme to its substrate?	Lock and Key Model.
72	What is the optimum pH for enzyme activity?	Usually around pH 7 (physiological pH).
73	What is the effect of high temperature on enzyme activity?	Denaturation (loss of activity).
74	What are Hormones?	Chemical messengers secreted by endocrine glands directly into the bloodstream.
75	Give two examples of protein-based hormones.	Insulin and Glucagon.
76	Give two examples of steroid-based hormones.	Estrogen and Testosterone.
77	What is the function of Insulin?	Regulates blood sugar levels (lowers glucose concentration).
78	What is the primary cause of Diabetes Mellitus?	Insulin deficiency or resistance.

Part 6: Vitamins

Q. No.	Question	Answer
79	What are Vitamins?	Organic compounds required in the diet in small amounts to perform specific biological functions for growth and health.
80	How are vitamins classified based on solubility?	Fat-soluble and Water-soluble.
81	Name the four Fat-Soluble vitamins.	A, D, E, K.
82	Name two Water-Soluble vitamins.	B-group vitamins and Vitamin C.
83	What is the chemical name for Vitamin A?	Retinol.
84	What deficiency disease is caused by a lack of Vitamin A?	Night Blindness (Xerophthalmia).
85	What is the chemical name for Vitamin C?	Ascorbic Acid.
86	What deficiency disease is caused by a lack of Vitamin C?	Scurvy.
87	What is the chemical name for Vitamin D?	Calciferol.
88	What deficiency disease is caused by a lack of Vitamin D?	Rickets (in children) or Osteomalacia (in adults).
89	What is the chemical name for Vitamin E?	Tocopherol.
90	What is the function of Vitamin K?	Essential for blood clotting (Coagulation).
91	What is the deficiency disease caused by a lack of Vitamin B1​?	Beri-beri.
92	Why must water-soluble vitamins be supplied regularly in the diet?	They are excreted in the urine and cannot be stored in the body.

Part 7: Miscellaneous Concepts

Q. No.	Question	Answer
93	What is the term for the storage of excess glucose in the liver and muscles?	Glycogenesis (forming Glycogen).
94	What is the linkage between the two monosaccharides in Sucrose?	α,β-glycosidic linkage (between C−1 of α-glucose and C−2 of β-fructose).
95	What is the type of linkage that connects C−1 to C−4 in Amylose?	α-Glycosidic linkage.
96	What are the two types of H-bonds in the α-helix structure of proteins?	Intrachain H-bonds (within the same chain).
97	What is the primary use of RNA interference (RNAi)?	Gene silencing (switching off specific genes).
98	Why are all amino acids (except glycine) optically active?	They have a chiral α-carbon (four different groups attached).
99	What is the essential difference between the sugar in a DNA and an RNA nucleotide?	DNA sugar lacks an OH group at the C−2 position.
100	What is the primary role of Cholesterol in the human body?	Precursor for the synthesis of steroid hormones and Vitamin D.
101	What is the product of the hydrolysis of proteins?	α-Amino Acids.
102	What is the product of the hydrolysis of Starch?	D-Glucose.
103	What is the relationship between the pI and the net charge of an amino acid at pH<pI?	The amino acid has a net positive charge (NH3+​ dominates).
104	What is the relationship between the pI and the net charge of an amino acid at pH>pI?	The amino acid has a net negative charge (COO− dominates).
105	What is a Chromoprotein?	A protein that contains a colored prosthetic group (e.g., Hemoglobin).
106	What is the full form of ATP?	Adenosine Triphosphate (the energy currency of the cell).
107	What is the bond that releases a large amount of energy upon hydrolysis in ATP?	Phosphate anhydride bond (high-energy bond).
108	What is the term for the sequence of three bases on tRNA that pairs with the codon on mRNA?	Anticodon.
109	What is the term for the three-dimensional structure of a single polypeptide chain stabilized by various bonds?	Tertiary Structure.
110	What is the main structural feature of the β-pleated sheet?	Lateral H-bonding between adjacent polypeptide chains.
111	Why is the DNA molecule acidic?	Due to the presence of Phosphate Groups (H3​PO4​ backbone).
112	What is the name of the bond that links the base to the sugar in a nucleoside?	N-glycosidic linkage (C−1 of sugar to N−1 or N−9 of base).

Quiz Revision Notes Downloads

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