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Biomolecules — NEET Biology MCQs with Solutions
Free NEET Biology Biomolecules MCQs with step-by-step solutions covering Chemical Composition & Metabolites, Proteins & Amino Acids, Carbohydrates & Nucleic Acids, Structure of Proteins & Metabolism, Enzymes. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Chemical Composition & Metabolites · easy · theory
Compounds with molecular weight less than ~1000 Da found in the acid-soluble pool are called:
A. Polymers only
B. Macromolecules
C. Micromolecules (e.g. sugars, amino acids) ✓ Correct
D. Enzymes
Solution: Micromolecules (mol. wt < 1000 Da) form the acid-soluble pool; macromolecules (> 10 kDa) are in the acid-insoluble fraction.
Q2 — Chemical Composition & Metabolites · easy · theory
Alkaloids, flavonoids, rubber and essential oils are examples of:
A. Primary metabolites
B. Secondary metabolites ✓ Correct
C. Enzymes
D. Biomacromolecules
Solution: Secondary metabolites have no obvious direct role in normal physiology but are useful (drugs, pigments, defence).
Q3 — Proteins & Amino Acids · easy · theory
The number of amino acids that commonly occur in proteins is:
A. 4
B. 10
C. 64
D. 20 ✓ Correct
Solution: Twenty standard amino acids make up proteins; each has an amino group, carboxyl group, H and an R group on the α-carbon.
Q4 — Proteins & Amino Acids · easy · theory
The bond that links two amino acids in a protein is the:
A. Hydrogen bond
B. Phosphodiester bond
C. Peptide bond ✓ Correct
D. Glycosidic bond
Solution: A peptide (amide) bond forms between the –COOH of one amino acid and the –NH₂ of the next, with loss of water.
Q5 — Carbohydrates & Nucleic Acids · easy · theory
The most abundant carbohydrate (and organic macromolecule) in nature, forming plant cell walls, is:
A. Cellulose ✓ Correct
B. Chitin
C. Starch
D. Glycogen
Solution: Cellulose (a homopolymer of glucose) is the most abundant polysaccharide; it forms plant cell walls.
Q6 — Carbohydrates & Nucleic Acids · easy · theory
The nitrogenous bases in DNA are adenine, guanine, cytosine and:
A. Thymine ✓ Correct
B. Xanthine
C. Uracil
D. Hypoxanthine
Solution: DNA contains thymine; in RNA, uracil replaces thymine.
Q7 — Structure of Proteins & Metabolism · easy · theory
The linear sequence of amino acids in a polypeptide is its ______ structure:
A. Tertiary
B. Quaternary
C. Primary ✓ Correct
D. Secondary
Solution: Primary structure = amino acid sequence; the first amino acid (N-terminal) and last (C-terminal) mark the ends.
Q8 — Structure of Proteins & Metabolism · easy · theory
The sum total of all the chemical reactions occurring in a cell/body is called:
A. Catalysis
B. Osmosis
C. Metabolism ✓ Correct
D. Diffusion
Solution: Metabolism includes anabolic (build-up) and catabolic (break-down) reactions; no metabolite exists in isolation.
Q9 — Enzymes · easy · theory
Enzymes are biological catalysts that speed up reactions by:
A. Lowering the activation energy ✓ Correct
B. Being consumed in the reaction
C. Changing the equilibrium constant
D. Raising the activation energy
Solution: Enzymes lower the activation energy of a reaction; they are not used up and do not alter the equilibrium.
Q10 — Enzymes · easy · theory
The specific region of an enzyme where the substrate binds is the:
A. Allosteric site only
B. Cofactor
C. Active site ✓ Correct
D. Backbone
Solution: The active site is a crevice/pocket shaped to fit specific substrate(s) forming an enzyme–substrate complex.
Q11 — Chemical Composition & Metabolites · hard · theory
When living tissue is ground with trichloroacetic acid and filtered, proteins, nucleic acids and polysaccharides are found in the:
A. Acid-soluble filtrate
B. Ash only
C. Acid-insoluble (retentate) fraction ✓ Correct
D. Gaseous phase
Solution: Macromolecules (proteins, nucleic acids, polysaccharides, lipids) form the acid-insoluble pool; micromolecules pass into the filtrate.
Q12 — Chemical Composition & Metabolites · hard · theory
Lipids, though sometimes below 800 Da, are found in the acid-INSOLUBLE (macromolecular) fraction because:
A. They have very high molecular weight
B. They dissolve in acid
C. They form part of membranes and come down as vesicles, not truly free molecules ✓ Correct
D. They are true polymers
Solution: Membrane lipids sediment as vesicular structures with the macromolecular fraction, an exception to the size rule.
Q13 — Proteins & Amino Acids · hard · theory
A zwitterion form of an amino acid exists at physiological pH because:
A. Both groups are neutral
B. The R group is always charged
C. It has no charge at any pH
D. The amino group is protonated (+) and the carboxyl group is ionised (−) simultaneously ✓ Correct
Solution: At neutral pH amino acids bear both a positive (–NH₃⁺) and a negative (–COO⁻) charge — the zwitterion (dipolar) form.
Q14 — Proteins & Amino Acids · hard · theory
The average molecular mass of an amino acid residue in a protein (~110 Da) is less than the free amino acid because:
A. Amino acids gain mass on polymerising
B. The R group is removed
C. A molecule of water is lost during each peptide bond formation ✓ Correct
D. Proteins contain no water
Solution: Peptide bond formation is a condensation (dehydration), so each residue is lighter than the free amino acid by ~18 Da.
Q15 — Carbohydrates & Nucleic Acids · hard · theory
Purines and pyrimidines differ structurally in that purines (adenine, guanine) are:
A. Both contain phosphate
B. Both single-ringed
C. Single-ringed, pyrimidines double-ringed
D. Double-ringed, while pyrimidines are single-ringed ✓ Correct
Solution: Purines (A, G) have a fused double-ring; pyrimidines (C, T, U) have a single six-membered ring.
Q16 — Carbohydrates & Nucleic Acids · hard · theory
The linkage between the two strands of DNA is by ______ bonds between complementary bases (A=T, G≡C):
A. Hydrogen ✓ Correct
B. Phosphodiester
C. Peptide
D. Glycosidic
Solution: The two antiparallel strands are held by hydrogen bonds (2 between A–T, 3 between G–C); the backbone is joined by phosphodiester bonds.
Q17 — Structure of Proteins & Metabolism · hard · theory
The "living state" (metabolism) is a NON-equilibrium steady state because:
A. Metabolism ceases at steady state
B. A cell is at chemical equilibrium
C. Reactions stop in living cells
D. A living cell is a system at steady state, kept away from equilibrium by constant energy input ✓ Correct
Solution: Reaching equilibrium means death; living systems maintain a steady state far from equilibrium via continuous energy flow.
Q18 — Structure of Proteins & Metabolism · hard · theory
Which best describes the "dynamic state of body constituents"?
A. Only carbohydrates turn over
B. Metabolism has no direction
C. Biomolecules are continuously being made and broken down (turnover) ✓ Correct
D. Biomolecules never change once formed
Solution: Body constituents undergo constant turnover (synthesis and degradation) — the dynamic (not static) state of metabolism.
Q19 — Enzymes · hard · theory
A competitive inhibitor decreases enzyme activity because it:
A. Resembles the substrate and competes for the active site ✓ Correct
B. Denatures the enzyme permanently
C. Binds the allosteric site only
D. Increases substrate concentration
Solution: Competitive inhibitors (e.g. malonate for succinic dehydrogenase) resemble the substrate and can be overcome by more substrate.
Q20 — Enzymes · hard · theory
In the six IUB classes of enzymes, an enzyme catalysing the transfer of a phosphate group between substrates is a:
A. Hydrolase
B. Oxidoreductase
C. Transferase ✓ Correct
D. Lyase
Solution: Transferases move a group (e.g. phosphate) between molecules; oxidoreductases handle redox, hydrolases hydrolyse bonds, lyases add/remove groups forming double bonds.
Q21 — Chemical Composition & Metabolites · medium · theory
Amino acids, glucose, nucleotides and fatty acids are examples of:
A. Non-biological molecules
B. Only macromolecules
C. Secondary metabolites
D. Primary metabolites ✓ Correct
Solution: Primary metabolites have identifiable functions in normal physiological processes.
Q22 — Chemical Composition & Metabolites · medium · theory
The most abundant chemical in a living cell (and the medium of biochemical reactions) is:
A. Water ✓ Correct
B. Protein
C. Carbohydrate
D. Lipid
Solution: Water constitutes ~70–90% of cell mass and is the most abundant molecule; proteins are the most abundant macromolecule.
Q23 — Proteins & Amino Acids · medium · theory
The nature of an amino acid (acidic, basic or neutral) is decided by its:
A. Amino group
B. Carboxyl group
C. R group (side chain) ✓ Correct
D. Alpha carbon
Solution: The R group determines the chemical/functional character of the amino acid (e.g. glutamic acid = acidic, lysine = basic).
Q24 — Proteins & Amino Acids · medium · theory
Amino acids that cannot be synthesised by the human body and must be taken in the diet are called:
A. Essential amino acids ✓ Correct
B. Semi-essential amino acids
C. Non-essential amino acids
D. Secondary metabolites
Solution: Essential amino acids must be obtained from food; the body can synthesise non-essential ones.
Q25 — Carbohydrates & Nucleic Acids · medium · theory
The bond joining monosaccharide units in a polysaccharide is a ______ bond:
A. Peptide
B. Phosphodiester
C. Glycosidic ✓ Correct
D. Ester
Solution: Glycosidic bonds link sugar residues; nucleotides are joined by phosphodiester bonds and amino acids by peptide bonds.
Q26 — Carbohydrates & Nucleic Acids · medium · theory
A nucleotide consists of a nitrogenous base + a ______ sugar + a phosphate group:
A. Tetrose
B. Hexose
C. Triose
D. Pentose ✓ Correct
Solution: Nucleotides contain a pentose (ribose in RNA, deoxyribose in DNA); base + sugar (without phosphate) is a nucleoside.
Q27 — Structure of Proteins & Metabolism · medium · theory
The three-dimensional folding of a polypeptide into a hollow woolen-ball-like form is its ______ structure:
A. Primary
B. Tertiary ✓ Correct
C. Quaternary
D. Secondary
Solution: Tertiary structure is the overall 3-D shape essential for biological function; quaternary is the arrangement of multiple subunits.
Q28 — Structure of Proteins & Metabolism · medium · theory
Haemoglobin, made of four subunits, illustrates the ______ structure of proteins:
A. Secondary
B. Primary
C. Quaternary ✓ Correct
D. Tertiary
Solution: Quaternary structure describes the spatial arrangement of two or more polypeptide chains (e.g. 4 subunits of Hb).
Q29 — Enzymes · medium · theory
The non-protein component required by some enzymes for activity is a ______; if it is a tightly bound organic molecule it is a ______:
A. Substrate; product
B. Coenzyme; substrate
C. Cofactor; prosthetic group ✓ Correct
D. Inhibitor; activator
Solution: Cofactors may be prosthetic groups (tightly bound), coenzymes (loosely bound organic, e.g. NAD) or metal ions.
Q30 — Enzymes · medium · theory
Enzyme activity typically shows an optimum with respect to temperature and pH because beyond the optimum the enzyme:
A. Denatures / loses its active conformation ✓ Correct
B. Becomes a substrate
C. Gains a cofactor
D. Increases activity indefinitely
Solution: Enzymes work best at an optimum T and pH; high temperature/extreme pH denatures the protein, abolishing activity.