Chapter 9: Biomolecules – MCQs
🔬 Biomolecules – MCQs
Part 1 (Q1–Q25)
Q1. Biomolecules containing C, H, and O in ~1:2:1 ratio are
A) Proteins
B) Carbohydrates ✅
C) Lipids
D) Nucleic acids
Explanation: Carbohydrates generally follow (CH₂O)ₙ empirical formula.
Q2. The building blocks of proteins are
A) Monosaccharides
B) Fatty acids
C) Amino acids ✅
D) Nucleotides
Explanation: Proteins are polymers of α-amino acids linked by peptide bonds.
Q3. The bond linking two amino acids is
A) Glycosidic bond
B) Phosphodiester bond
C) Peptide bond ✅
D) Disulfide bond
Explanation: Peptide bond forms between –COOH of one amino acid and –NH₂ of another.
Q4. The major storage polysaccharide in plants is
A) Glycogen
B) Starch ✅
C) Cellulose
D) Chitin
Explanation: Starch (amylose + amylopectin) stores glucose in plants.
Q5. The major storage polysaccharide in animals is
A) Starch
B) Cellulose
C) Glycogen ✅
D) Inulin
Explanation: Glycogen is a highly branched α-(1→4,1→6) glucose polymer.
Q6. Structural polysaccharide in plant cell walls is
A) Cellulose ✅
B) Chitin
C) Pectin
D) Hemicellulose
Explanation: Cellulose is β-(1→4) D-glucose forming microfibrils.
Q7. The test to detect reducing sugars is
A) Biuret test
B) Benedict’s test ✅
C) Sudan III test
D) Iodine test
Explanation: Benedict’s (or Fehling’s) detects reducing sugars via Cu²⁺ → Cu₂O.
Q8. The test to detect proteins is
A) Iodine test
B) Biuret test ✅
C) Molisch test
D) Ninhydrin test
Explanation: Biuret gives violet with peptide bonds (Cu²⁺ complex).
Q9. The test that gives blue-black color with starch is
A) Benedict’s
B) Iodine test ✅
C) Ninhydrin
D) Barfoed’s
Explanation: Iodine fits into amylose helix, giving blue-black color.
Q10. Lipids are insoluble in water but soluble in
A) Dilute acids
B) Organic solvents ✅
C) Alkaline water
D) Saline
Explanation: Lipids dissolve in non-polar solvents (ether, chloroform).
Q11. Saturated fatty acids have
A) No double bonds ✅
B) One double bond
C) Many double bonds
D) Triple bonds
Explanation: Saturated chains contain only C–C single bonds.
Q12. The bond linking nucleotides in DNA/RNA backbone is
A) Peptide
B) Glycosidic
C) Phosphodiester ✅
D) Disulfide
Explanation: 3′→5′ phosphodiester bonds connect sugar-phosphate backbone.
Q13. Nitrogenous base not found in RNA is
A) Uracil
B) Adenine
C) Cytosine
D) Thymine ✅
Explanation: RNA has uracil; DNA has thymine.
Q14. The sugar present in DNA is
A) Ribose
B) Deoxyribose ✅
C) Glucose
D) Fructose
Explanation: DNA contains 2-deoxyribose; RNA has ribose.
Q15. Enzymes are chemically
A) Carbohydrates
B) Proteins ✅
C) Lipids
D) Nucleic acids
Explanation: Most enzymes are proteins (some RNA enzymes are ribozymes).
Q16. The non-protein part of a conjugated enzyme is
A) Apoenzyme
B) Holoenzyme
C) Cofactor ✅
D) Zymogen
Explanation: Cofactor (metal ion or coenzyme/prosthetic group) + apoenzyme = holoenzyme.
Q17. Vitamin functioning as part of FAD is
A) Vitamin B₂ (riboflavin) ✅
B) Vitamin B₁
C) Vitamin B₆
D) Vitamin C
Explanation: Riboflavin forms FAD/FMN coenzymes for redox reactions.
Q18. The temperature at which enzyme activity is maximal is termed
A) Activation energy
B) Optimum temperature ✅
C) Denaturation point
D) Melting point
Explanation: Optimum temperature maximizes enzyme catalytic rate without denaturation.
Q19. Competitive inhibition can be overcome by
A) Lowering pH
B) Increasing substrate concentration ✅
C) Increasing inhibitor
D) Denaturing enzyme
Explanation: Competitive inhibitor competes at active site; more substrate outcompetes it.
Q20. The primary structure of a protein refers to
A) 3D shape
B) Sequence of amino acids ✅
C) α-helix/β-sheet
D) Subunit association
Explanation: Primary structure is the linear amino acid sequence.
Q21. Disulfide bonds commonly stabilize
A) Primary structure
B) Secondary structure
C) Tertiary structure ✅
D) Phospholipids
Explanation: –S–S– bonds between cysteines stabilize tertiary (and sometimes quaternary) structure.
Q22. The lipid forming biological membranes is mainly
A) Triglyceride
B) Steroid
C) Phospholipid ✅
D) Waxes
Explanation: Phospholipid bilayer forms core of cell membranes.
Q23. Essential amino acids are those
A) Synthesized by body
B) Only in plants
C) Must be obtained from diet ✅
D) Non-proteinogenic
Explanation: Essential AAs (e.g., lysine, methionine) cannot be synthesized by humans.
Q24. The most abundant biomolecule on Earth is
A) Glycogen
B) Starch
C) Cellulose ✅
D) Chitin
Explanation: Cellulose is the most abundant organic polymer (plant biomass).
Q25. The energy currency of cell is
A) NADH
B) ATP ✅
C) FAD
D) GTP
Explanation: ATP stores/transfers energy via high-energy phosphate bonds.
🔬 Cell Structure and Function — Biomolecules
Part 2 (Q26–Q50)
Q26. The secondary structure of proteins is stabilized by
A) Disulfide bonds
B) Peptide bonds
C) Hydrogen bonds ✅
D) Ionic bonds
Explanation: α-helix and β-sheet in secondary structure are stabilized by H-bonds between peptide backbones.
Q27. The quaternary structure of a protein refers to
A) Peptide sequence
B) Folding of a single chain
C) Interaction of multiple polypeptide subunits ✅
D) α-helix and β-sheet
Explanation: Quaternary structure = association of more than one polypeptide (e.g., hemoglobin).
Q28. The most abundant protein in the human body is
A) Hemoglobin
B) Collagen ✅
C) Myosin
D) Insulin
Explanation: Collagen (connective tissue protein) is the most abundant in humans.
Q29. Enzymes that add phosphate groups are called
A) Phosphatases
B) Kinases ✅
C) Ligases
D) Oxidases
Explanation: Kinases catalyze transfer of phosphate from ATP to substrates.
Q30. Enzymes that remove phosphate groups are called
A) Phosphatases ✅
B) Kinases
C) Transferases
D) Hydrolases
Explanation: Phosphatases hydrolyze phosphate esters, removing phosphate groups.
Q31. The energy-rich bond in ATP is between
A) Ribose and adenine
B) Adenine and phosphate
C) Phosphate and phosphate (terminal bonds) ✅
D) Ribose and phosphate
Explanation: High-energy bonds in ATP are phosphoanhydride bonds between phosphates.
Q32. Enzymes lower
A) Free energy
B) Entropy
C) Activation energy ✅
D) Bond strength
Explanation: Enzymes reduce activation energy, not ΔG of the reaction.
Q33. Which one is a disaccharide?
A) Glucose
B) Maltose ✅
C) Starch
D) Cellulose
Explanation: Maltose = glucose + glucose (α-1,4 linkage).
Q34. Which is a homopolysaccharide?
A) Starch ✅
B) Glycoprotein
C) Peptidoglycan
D) Glycolipid
Explanation: Starch is a polymer of only glucose units.
Q35. Which is a heteropolysaccharide?
A) Glycogen
B) Cellulose
C) Hyaluronic acid ✅
D) Starch
Explanation: Hyaluronic acid contains alternating uronic acid and amino sugars.
Q36. The monomer of nucleic acids is
A) Amino acid
B) Monosaccharide
C) Nucleotide ✅
D) Fatty acid
Explanation: Nucleotides (sugar + base + phosphate) are building blocks of DNA/RNA.
Q37. Purines include
A) Adenine and guanine ✅
B) Cytosine and thymine
C) Uracil and cytosine
D) Thymine and uracil
Explanation: Purines = double-ring bases (adenine, guanine); pyrimidines = single-ring.
Q38. Pyrimidines include
A) Adenine, guanine
B) Cytosine, thymine, uracil ✅
C) Guanine, cytosine
D) Adenine, uracil
Explanation: Pyrimidines = single-ring bases: C, T, U.
Q39. DNA has base pairing according to
A) Meselson-Stahl rule
B) Chargaff’s rule ✅
C) Central dogma
D) Watson–Crick law
Explanation: Chargaff’s rule: A=T and G≡C (purine = pyrimidine).
Q40. Which is a pentose sugar?
A) Glucose
B) Ribose ✅
C) Fructose
D) Galactose
Explanation: Ribose (RNA) and deoxyribose (DNA) are pentose sugars.
Q41. Cholesterol is chemically a
A) Protein
B) Steroid ✅
C) Fatty acid
D) Polysaccharide
Explanation: Cholesterol is a steroid lipid regulating membrane fluidity.
Q42. Which vitamin is fat-soluble?
A) Vitamin B
B) Vitamin C
C) Vitamin D ✅
D) Vitamin B₁₂
Explanation: Vitamins A, D, E, K are fat-soluble.
Q43. Which vitamin is water-soluble?
A) Vitamin A
B) Vitamin K
C) Vitamin B-complex ✅
D) Vitamin D
Explanation: B-complex and C are water-soluble vitamins.
Q44. The coenzyme NAD⁺ is derived from
A) Vitamin B₆
B) Niacin (Vitamin B₃) ✅
C) Riboflavin
D) Vitamin C
Explanation: Niacin forms NAD⁺/NADP⁺, important in redox reactions.
Q45. The coenzyme FAD is derived from
A) Vitamin C
B) Vitamin B₂ (riboflavin) ✅
C) Vitamin K
D) Vitamin B₁₂
Explanation: Riboflavin forms FAD/FMN coenzymes for dehydrogenases.
Q46. The structural polysaccharide in exoskeleton of insects is
A) Cellulose
B) Chitin ✅
C) Pectin
D) Hemicellulose
Explanation: Chitin (N-acetylglucosamine) forms insect and crustacean exoskeleton.
Q47. DNA replication follows
A) Conservative model
B) Semiconservative model ✅
C) Dispersive model
D) Rolling circle
Explanation: Meselson & Stahl proved DNA replication is semiconservative.
Q48. The melting temperature (Tm) of DNA depends on
A) A–T content
B) G–C content ✅
C) DNA length only
D) Protein content
Explanation: G≡C bonds (3 H-bonds) raise DNA melting temperature.
Q49. Which is not a component of a nucleotide?
A) Nitrogenous base
B) Pentose sugar
C) Phosphate
D) Amino acid ✅
Explanation: Nucleotide = base + sugar + phosphate (no amino acid).
Q50. Enzymes are specific due to
A) Cofactors
B) Active site ✅
C) Coenzymes
D) Substrate
Explanation: Enzyme specificity arises from the 3D structure of the active site.
🔬 Cell Structure and Function — Biomolecules
Part 3 (Q51–Q75)
Q51. DNA is made up of
A) Deoxyribose sugar, phosphate, and nitrogenous bases ✅
B) Ribose sugar, phosphate, bases
C) Amino acids and nucleotides
D) Fatty acids and bases
Explanation: DNA = deoxyribose sugar + phosphate backbone + nitrogen bases (A, T, G, C).
Q52. RNA differs from DNA in having
A) Adenine
B) Ribose sugar ✅
C) Guanine
D) Phosphate
Explanation: RNA contains ribose sugar and uracil instead of thymine.
Q53. In DNA, A always pairs with
A) G
B) C
C) T ✅
D) U
Explanation: According to Chargaff’s rule, A=T (2 H-bonds), G≡C (3 H-bonds).
Q54. In RNA, A pairs with
A) T
B) U ✅
C) C
D) G
Explanation: RNA lacks thymine, so adenine pairs with uracil.
Q55. The double-helix model of DNA was proposed by
A) Watson and Crick ✅
B) Franklin and Wilkins
C) Meselson and Stahl
D) Hershey and Chase
Explanation: Watson & Crick (1953) proposed the double-helix model of DNA.
Q56. Which of the following is a storage lipid?
A) Triglycerides ✅
B) Phospholipids
C) Steroids
D) Glycolipids
Explanation: Triglycerides (fats) store energy in animals.
Q57. Which lipid regulates membrane fluidity?
A) Triglyceride
B) Cholesterol ✅
C) Glycolipid
D) Waxes
Explanation: Cholesterol maintains membrane fluidity and stability.
Q58. The enzyme which joins Okazaki fragments is
A) DNA polymerase
B) DNA ligase ✅
C) RNA polymerase
D) Helicase
Explanation: DNA ligase seals nicks and joins Okazaki fragments in lagging strand.
Q59. The repeating unit of a polypeptide chain is
A) Amino acid ✅
B) Nucleotide
C) Fatty acid
D) Monosaccharide
Explanation: Proteins are polymers of amino acids.
Q60. Glycosidic bonds are found in
A) Proteins
B) Nucleic acids
C) Carbohydrates ✅
D) Lipids
Explanation: Glycosidic bonds link monosaccharides in disaccharides & polysaccharides.
Q61. The bond between base and sugar in a nucleotide is
A) Glycosidic bond ✅
B) Phosphodiester bond
C) Peptide bond
D) Hydrogen bond
Explanation: Base + sugar = nucleoside (glycosidic bond); nucleoside + phosphate = nucleotide.
Q62. A nucleotide without phosphate group is called
A) Nucleoside ✅
B) Amino acid
C) Monosaccharide
D) Base
Explanation: Nucleoside = base + sugar; addition of phosphate gives nucleotide.
Q63. The process of RNA formation from DNA is
A) Translation
B) Transcription ✅
C) Replication
D) Mutation
Explanation: Transcription = synthesis of RNA from DNA template.
Q64. The process of protein synthesis from mRNA is
A) Replication
B) Transcription
C) Translation ✅
D) Mutation
Explanation: Translation occurs at ribosomes, decoding mRNA into protein.
Q65. Which is a storage polysaccharide in animals?
A) Starch
B) Glycogen ✅
C) Cellulose
D) Inulin
Explanation: Glycogen stores glucose in animals & fungi.
Q66. Which is a storage polysaccharide in plants?
A) Glycogen
B) Starch ✅
C) Chitin
D) Cellulose
Explanation: Starch (amylose + amylopectin) is plant glucose storage.
Q67. The RNA carrying amino acids to ribosomes is
A) mRNA
B) tRNA ✅
C) rRNA
D) snRNA
Explanation: tRNA delivers specific amino acids during translation.
Q68. The RNA forming ribosomes is
A) mRNA
B) rRNA ✅
C) tRNA
D) snRNA
Explanation: rRNA + proteins form ribosomal subunits.
Q69. Which RNA carries genetic information from DNA?
A) rRNA
B) mRNA ✅
C) tRNA
D) snRNA
Explanation: mRNA carries coding sequences from DNA → protein synthesis.
Q70. The start codon in mRNA is
A) UAA
B) UGA
C) AUG ✅
D) UAG
Explanation: AUG codes for methionine, the universal start codon.
Q71. Stop codons are
A) UAA, UAG, UGA ✅
B) AUG, GUG
C) UAC, UGC, UGG
D) AAA, AUA
Explanation: UAA, UAG, UGA are nonsense codons (stop translation).
Q72. A polymer of fructose units is
A) Cellulose
B) Inulin ✅
C) Glycogen
D) Amylose
Explanation: Inulin is a fructose-storage polysaccharide in plants (e.g., Dahlia).
Q73. Lactose is composed of
A) Glucose + Glucose
B) Glucose + Galactose ✅
C) Glucose + Fructose
D) Galactose + Fructose
Explanation: Lactose = glucose + galactose (β-1,4 linkage).
Q74. Sucrose is composed of
A) Glucose + Glucose
B) Glucose + Galactose
C) Glucose + Fructose ✅
D) Galactose + Fructose
Explanation: Sucrose = glucose + fructose (α-1,2 linkage).
Q75. Which polysaccharide is indigestible to humans?
A) Starch
B) Cellulose ✅
C) Glycogen
D) Maltose
Explanation: Humans lack cellulase enzyme, so cellulose is indigestible.
🔬 Cell Structure and Function — Biomolecules
Part 4 (Q76–Q100)
Q76. The enzyme DNA polymerase catalyzes
A) Protein synthesis
B) DNA replication ✅
C) RNA synthesis
D) ATP hydrolysis
Explanation: DNA polymerase synthesizes new DNA strands during replication.
Q77. The enzyme RNA polymerase catalyzes
A) Translation
B) Transcription ✅
C) Replication
D) DNA repair
Explanation: RNA polymerase synthesizes RNA from a DNA template.
Q78. Which of the following is a ribozyme?
A) tRNA
B) rRNA ✅
C) DNA
D) Protein enzyme
Explanation: rRNA can act as an enzyme in ribosome (peptidyl transferase activity).
Q79. Hemoglobin is a
A) Monomer
B) Tetramer ✅
C) Dimer
D) Trimer
Explanation: Hemoglobin has 4 polypeptide subunits (2α, 2β).
Q80. Insulin is a
A) Monosaccharide
B) Protein hormone ✅
C) Steroid hormone
D) Vitamin
Explanation: Insulin is a peptide hormone regulating blood glucose.
Q81. Testosterone is chemically a
A) Protein
B) Steroid ✅
C) Peptide
D) Vitamin
Explanation: Testosterone is a steroid hormone derived from cholesterol.
Q82. The sugar present in ATP is
A) Glucose
B) Ribose ✅
C) Deoxyribose
D) Fructose
Explanation: ATP contains ribose sugar with adenine and three phosphate groups.
Q83. The enzyme which unwinds DNA during replication is
A) Ligase
B) Helicase ✅
C) Polymerase
D) Primase
Explanation: Helicase unwinds DNA strands by breaking hydrogen bonds.
Q84. The enzyme that synthesizes RNA primer is
A) DNA polymerase
B) Primase ✅
C) Ligase
D) Helicase
Explanation: Primase synthesizes RNA primers to initiate DNA replication.
Q85. The enzyme that proofreads DNA replication is
A) RNA polymerase
B) DNA polymerase I ✅
C) DNA ligase
D) Topoisomerase
Explanation: DNA polymerase I removes RNA primers and proofreads new DNA strands.
Q86. The hereditary material in most viruses is
A) DNA or RNA ✅
B) Protein
C) Carbohydrate
D) Lipid
Explanation: Viruses may have DNA (e.g., bacteriophages) or RNA (e.g., HIV) genomes.
Q87. The most abundant RNA in cells is
A) mRNA
B) tRNA
C) rRNA ✅
D) snRNA
Explanation: rRNA forms ribosomes and is the most abundant RNA (~80%).
Q88. The smallest RNA in cells is
A) rRNA
B) mRNA
C) tRNA ✅
D) hnRNA
Explanation: tRNA is the smallest (~70–90 nucleotides).
Q89. The first amino acid in eukaryotic protein synthesis is
A) Glycine
B) Methionine ✅
C) Alanine
D) Valine
Explanation: The start codon AUG codes for methionine in eukaryotes.
Q90. The first amino acid in prokaryotic protein synthesis is
A) Methionine
B) Formyl-methionine (fMet) ✅
C) Glycine
D) Alanine
Explanation: Prokaryotes initiate protein synthesis with fMet-tRNA.
Q91. The bond between DNA strands is
A) Ionic
B) Hydrogen ✅
C) Covalent
D) Peptide
Explanation: Complementary DNA strands are held by H-bonds (A=T, G≡C).
Q92. Histones are rich in
A) Acidic amino acids
B) Basic amino acids (lysine, arginine) ✅
C) Sulfur-containing amino acids
D) Aromatic amino acids
Explanation: Histones bind DNA (negatively charged) due to their basic residues.
Q93. The enzyme reverse transcriptase synthesizes
A) Protein
B) DNA from RNA ✅
C) RNA from DNA
D) DNA from DNA
Explanation: Reverse transcriptase converts viral RNA → complementary DNA.
Q94. Which element is most abundant in living matter?
A) Nitrogen
B) Oxygen ✅
C) Calcium
D) Phosphorus
Explanation: Oxygen is most abundant (~65%) in living organisms.
Q95. Which element is known as the “backbone of biomolecules”?
A) Hydrogen
B) Nitrogen
C) Carbon ✅
D) Phosphorus
Explanation: Carbon forms stable covalent bonds, making it the backbone of life.
Q96. The bond between nucleotides in DNA/RNA backbone is
A) Peptide
B) Phosphodiester ✅
C) Hydrogen
D) Disulfide
Explanation: Phosphodiester bonds link sugar-phosphate groups of nucleotides.
Q97. Which carbohydrate is used for energy storage in animals?
A) Cellulose
B) Glycogen ✅
C) Inulin
D) Pectin
Explanation: Glycogen is the main storage form of glucose in animals.
Q98. The vitamin required for vision is
A) Vitamin C
B) Vitamin D
C) Vitamin A ✅
D) Vitamin K
Explanation: Vitamin A (retinol) is required for synthesis of rhodopsin in the retina.
Q99. The vitamin required for blood clotting is
A) Vitamin A
B) Vitamin K ✅
C) Vitamin D
D) Vitamin E
Explanation: Vitamin K is essential for prothrombin synthesis in clotting.
Q100. Which biomolecule directly carries genetic information?
A) Protein
B) DNA ✅
C) Lipid
D) Carbohydrate
Explanation: DNA is the genetic material in most organisms (except some RNA viruses).
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