60 free MCQs on Biomolecules with worked answers and explanations. The chemistry of life: carbohydrates, proteins, lipids, nucleic acids, enzymes, and vitamins. Understand their structures, classification, and biological functions. Highly relevant for NEET and Class 12 board exams.
Take the timed Biomolecules chapterwise test →Below are 60 practice questions on Biomolecules, sorted Easy → Hard. Tap “Show answer & explanation” under any question to check yourself. Want the full theory first? Read the Biomolecules notes.
Two amino acids join via a condensation reaction: the carboxyl -OH of one and an amine -H of the other are eliminated as water, leaving a peptide bond (-CO-NH-) linking them into a dipeptide; repeating this builds a full protein chain.
Q1.
Which biomolecule is the primary source of energy for living organisms?
Answer: A. Carbohydrates
Why: Carbohydrates (glucose) are the primary and most readily available energy source for cells.
Q2.
What is the monomer unit of proteins?
Answer: A. Amino acids
Why: Proteins are polymers of amino acids linked by peptide bonds.
Q3.
Which bond joins amino acids in proteins?
Answer: A. Peptide bond
Why: Amino acids are joined by peptide bonds (-CO-NH-) formed by condensation reactions.
Q4.
What is the monomer of starch and cellulose?
Answer: A. Glucose
Why: Both starch and cellulose are polysaccharides made up of glucose monomers.
Q5.
Which monosaccharide is found in blood as blood sugar?
Answer: B. Glucose
Why: Glucose is the blood sugar and the primary fuel for cellular respiration.
Q6.
DNA stands for:
Answer: A. Deoxyribonucleic acid
Why: DNA is deoxyribonucleic acid, the carrier of genetic information.
Q7.
Which base is present in DNA but NOT in RNA?
Answer: A. Thymine
Why: DNA contains thymine (T) while RNA has uracil (U) instead.
Q8.
Which base is present in RNA but NOT in DNA?
Answer: A. Uracil
Why: RNA contains uracil instead of thymine found in DNA.
Q9.
The double helix structure of DNA was proposed by:
Answer: A. Watson and Crick
Why: Watson and Crick proposed the double helix model of DNA in 1953.
Q10.
Which enzyme digests starch in saliva?
Answer: A. Amylase
Why: Salivary amylase begins starch digestion in the mouth.
Q11.
Fats are esters of glycerol and:
Answer: A. Fatty acids
Why: Triglycerides (fats) are formed by esterification of glycerol with three fatty acid molecules.
Q12.
Which vitamin is produced by the body when exposed to sunlight?
Answer: A. Vitamin D
Why: Vitamin D is synthesised in the skin upon UV exposure from sunlight.
Q13.
Sucrose is a disaccharide made of:
Answer: A. Glucose and fructose
Why: Sucrose (table sugar) is a disaccharide of glucose and fructose linked by a glycosidic bond.
Q14.
Which type of RNA carries amino acids to the ribosome during protein synthesis?
Answer: A. tRNA
Why: Transfer RNA (tRNA) carries specific amino acids to the ribosome where protein synthesis occurs.
Q15.
Lactose is found in:
Answer: A. Milk
Why: Lactose (milk sugar) is the disaccharide present in milk.
Q16.
Which element is present in proteins but NOT in carbohydrates or fats?
Answer: A. Nitrogen
Why: Proteins contain nitrogen (in amino groups) in addition to C, H, and O found in all three macromolecules.
Q17.
The storage form of glucose in animals is:
Answer: A. Glycogen
Why: Animals store glucose as glycogen, mainly in the liver and muscles.
Q18.
Cellulose is a structural component of:
Answer: A. Plant cell walls
Why: Cellulose provides structural rigidity to plant cell walls.
Q19.
Which of the following is NOT a monosaccharide?
Answer: A. Sucrose
Why: Sucrose is a disaccharide (glucose + fructose); the others are monosaccharides.
Q20.
Haemoglobin is a protein that contains which metal ion?
Answer: A. Iron (Fe<sup>2+</sup>)
Why: Haemoglobin contains iron (Fe<sup>2+</sup>) in its haem group, which binds oxygen.
Q21.
What is the primary structure of a protein?
Answer: A. Sequence of amino acids in the polypeptide chain
Why: Primary structure is the linear sequence of amino acids linked by peptide bonds.
Q22.
Which forces stabilise the alpha-helix secondary structure of proteins?
Answer: A. Hydrogen bonds between NH and C=O groups
Why: The alpha-helix is stabilised by intramolecular hydrogen bonds between the backbone NH and C=O.
Q23.
The Chargaff rule states that in DNA:
Answer: A. [A]=[T] and [G]=[C]
Why: Chargaff's rule: adenine pairs with thymine and guanine pairs with cytosine; so [A]=[T] and [G]=[C].
Q24.
What type of bond connects nucleotides in a DNA strand?
Answer: A. Phosphodiester bond
Why: Nucleotides in a polynucleotide chain are linked by phosphodiester bonds (3'-5' linkage).
Q25.
Which sugar is present in RNA?
Answer: A. Ribose
Why: RNA contains ribose sugar; DNA contains deoxyribose (lacking the 2'-OH group).
Q26.
Enzymes are biological catalysts that are primarily:
Answer: A. Proteins
Why: Most enzymes are proteins; some RNA molecules with catalytic activity are called ribozymes.
Q27.
The region of an enzyme where substrate binds is called the:
Answer: A. Active site
Why: The active site is the specific region of an enzyme that binds the substrate and catalyses the reaction.
Q28.
Reducing sugars give a positive test with:
Answer: A. Fehling's solution
Why: Reducing sugars (those with free aldehyde or keto groups) reduce Fehling's solution to Cu<sub>2</sub>O (brick-red).
Q29.
Which test is used to detect proteins?
Answer: A. Biuret test
Why: The Biuret test detects peptide bonds; proteins give a violet/purple colour with Cu<sup>2+</sup> in alkaline solution.
Q30.
Starch gives a blue-black colour with:
Answer: A. Iodine solution
Why: Iodine gets trapped in the helical structure of amylose in starch, giving the characteristic blue-black colour.
Q31.
Glycine is the simplest amino acid because:
Answer: A. Its R group is just a hydrogen atom
Why: Glycine has H as its side chain (R group), making it the smallest and simplest amino acid.
Q32.
Which amino acids form disulfide bridges in proteins?
Answer: A. Two cysteine residues
Why: Disulfide bonds (S-S) form between the -SH groups of two cysteine residues and stabilise tertiary structure.
Q33.
Denaturation of a protein involves:
Answer: A. Loss of 3D structure while primary structure remains intact
Why: Denaturation disrupts secondary, tertiary, and quaternary structures without breaking peptide bonds.
Q34.
Maltose is a disaccharide formed by:
Answer: A. Two glucose units linked by alpha 1,4-glycosidic bond
Why: Maltose is formed from two glucose units joined by an alpha-1,4 glycosidic bond.
Q35.
Which vitamin is involved in blood clotting?
Answer: A. Vitamin K
Why: Vitamin K is essential for the synthesis of clotting factors (e.g., prothrombin).
Q36.
What is the role of NAD+ in metabolism?
Answer: A. Electron/hydrogen carrier in oxidation-reduction reactions
Why: NAD+ (nicotinamide adenine dinucleotide) accepts electrons/hydrogen in metabolic oxidation reactions.
Q37.
Which part of the amino acid determines its properties?
Answer: A. R group (side chain)
Why: The R group (side chain) is unique to each amino acid and determines its chemical and physical properties.
Q38.
Lipids are not polymers because:
Answer: A. They are joined by ester bonds not polymerised like polysaccharides; no repeating monomer units
Why: Fats are triesters of glycerol and fatty acids, not true polymers made of repeating identical monomers.
Q39.
The Haworth projection represents:
Answer: A. Cyclic form of carbohydrates
Why: Haworth projections show the ring (cyclic hemiacetal) forms of monosaccharides like glucose.
Q40.
Insulin is a hormone that is chemically a:
Answer: A. Protein (polypeptide)
Why: Insulin is a peptide hormone made of two polypeptide chains linked by disulfide bonds.
Q41.
Which of the following is an essential amino acid?
Answer: A. Lysine
Why: Essential amino acids cannot be synthesised by the human body and must be obtained from diet. Lysine is one of the nine essential amino acids.
Q42.
The anomeric carbon in glucose is:
Answer: A. C-1 (the aldehyde carbon in the open chain)
Why: The anomeric carbon (C-1 in aldoses) is the one that forms the new chiral centre when the ring closes.
Q43.
Alpha-D-glucose and beta-D-glucose are:
Answer: A. Anomers (differ at the anomeric carbon)
Why: Alpha and beta glucose differ only in the configuration at C-1 (anomeric carbon) and are called anomers.
Q44.
In the beta-pleated sheet, adjacent polypeptide chains are held by:
Answer: A. Intermolecular hydrogen bonds between backbone groups
Why: Beta-sheets are stabilised by hydrogen bonds between NH and C=O groups on adjacent parallel or antiparallel chains.
Q45.
Mutation in DNA results from:
Answer: A. Change in base sequence
Why: A mutation is a permanent change in the nucleotide sequence of DNA, which can alter the protein encoded.
Q46.
Which enzyme catalyses the formation of peptide bonds during translation?
Answer: A. Peptidyl transferase (part of the ribosome)
Why: Peptidyl transferase, a ribozyme activity of the ribosomal RNA, catalyses peptide bond formation during translation.
Q47.
What is the isoelectric point (pI) of an amino acid?
Answer: A. The pH at which the amino acid has no net charge (zwitterion)
Why: At the isoelectric point, the amino acid exists as a neutral zwitterion with equal positive and negative charges.
Q48.
Nucleoside differs from nucleotide in that nucleoside:
Answer: A. Lacks the phosphate group
Why: A nucleoside = base + sugar; a nucleotide = base + sugar + phosphate.
Q49.
Which type of RNA has the shortest lifespan?
Answer: A. mRNA
Why: mRNA is highly unstable and has a short lifespan as it encodes transient instructions for protein synthesis.
Q50.
The glycosidic bond in cellulose is:
Answer: A. Beta-1,4 glycosidic bond
Why: Cellulose is formed from beta-D-glucose units linked by beta-1,4 glycosidic bonds, creating rigid linear chains.
Q51.
Which lipoprotein carries cholesterol from tissues back to the liver?
Answer: A. HDL
Why: HDL (high-density lipoprotein) is the 'good' cholesterol carrier that transports cholesterol to the liver for processing.
Q52.
Competitive inhibitors of enzymes:
Answer: A. Bind to the active site and compete with substrate
Why: Competitive inhibitors resemble the substrate and compete for the active site; they increase apparent Km but not Vmax.
Q53.
Zwitterion formation in amino acids occurs because:
Answer: A. The amino group accepts a proton from the carboxyl group intramolecularly
Why: In a zwitterion, the -COOH donates a proton to the -NH<sub>2</sub> group, giving -COO- and -NH<sub>3</sub><sup>+</sup>.
Q54.
Which of the following correctly describes the B-form of DNA?
Answer: A. Right-handed double helix, 10 base pairs per turn, major and minor grooves
Why: The B-form (Watson-Crick form) of DNA is a right-handed helix with 10 base pairs per turn and distinct major and minor grooves.
Q55.
Enzyme activity is maximum at the optimum temperature because:
Answer: A. Activation energy is minimum and protein structure is intact
Why: At the optimum temperature, enough thermal energy exists for reactions but the enzyme is not yet denatured.
Q56.
Which purine base pairs with thymine in DNA?
Answer: A. Adenine
Why: Adenine (a purine) pairs with thymine via two hydrogen bonds; guanine pairs with cytosine via three hydrogen bonds.
Q57.
Which level of protein structure is disrupted by reducing agents (breaking S-S bonds)?
Answer: A. Quaternary/Tertiary (disulfide bonds in tertiary structure)
Why: Disulfide bonds (covalent S-S) contribute to tertiary and quaternary structure; reducing agents cleave them.
Q58.
The lock-and-key model of enzyme action proposes:
Answer: A. Substrate shape exactly fits the rigid active site
Why: Lock-and-key model (Fischer): the enzyme has a rigid complementary shape to the substrate, like a lock and key.
Q59.
Which amino acid is responsible for the UV absorption of proteins at 280 nm?
Answer: A. Tryptophan (and tyrosine)
Why: Aromatic amino acids tryptophan and tyrosine absorb UV light at ~280 nm due to their pi electron systems.
Q60.
In gel electrophoresis of DNA, smaller fragments migrate:
Answer: A. Faster toward the positive electrode
Why: DNA is negatively charged and migrates toward the positive pole; smaller fragments migrate faster through the gel matrix.