Structure of Proteins & Metabolism — NEET Biology MCQs with Solutions

Solution: Primary structure = amino acid sequence; the first amino acid (N-terminal) and last (C-terminal) mark the ends.

Solution: Metabolism includes anabolic (build-up) and catabolic (break-down) reactions; no metabolite exists in isolation.

Solution: Tertiary structure is the overall 3-D shape essential for biological function; quaternary is the arrangement of multiple subunits.

Solution: Quaternary structure describes the spatial arrangement of two or more polypeptide chains (e.g. 4 subunits of Hb).

Solution: Reaching equilibrium means death; living systems maintain a steady state far from equilibrium via continuous energy flow.

Solution: Body constituents undergo constant turnover (synthesis and degradation) — the dynamic (not static) state of metabolism.

Solution: Secondary structure refers to regular patterns such as the α-helix and β-pleated sheet formed by the polypeptide backbone.

Solution: By convention the first amino acid, bearing the free –NH₂ group, is the N-terminal (left) end; the last is the C-terminal end.

Solution: The functional properties of a protein depend on its overall three-dimensional (tertiary) folding, which creates the active shape.

Solution: Metabolites are converted into one another through chains of enzyme-catalysed steps known as metabolic pathways.

Solution: Haemoglobin has quaternary structure built from four subunits, two α-globin and two β-globin chains, each with a haem group.

Solution: Tertiary folding results from various side-chain (R-group) interactions — hydrophobic, ionic, hydrogen and disulphide bonds — not from the peptide bonds themselves.

Solution: The primary structure is defined by peptide bonds and the amino acid sequence, not by hydrogen bonds between R-groups; that statement is incorrect.

Solution: Catabolic reactions degrade complex molecules to simpler ones and release energy; anabolic reactions build complex molecules and consume energy.

Solution: Secondary structures (α-helix, β-sheet) are indeed stabilised by backbone hydrogen bonding, so R correctly explains A.

Solution: Primary = sequence, secondary = local helix/sheet, tertiary = overall three-dimensional folding, quaternary = arrangement of multiple subunits.

Solution: The assertion is correct, but the assembly of multiple polypeptide subunits is the quaternary structure, not the secondary structure, so the reason is false.

Solution: Both statements are incorrect. The left end (N-terminal) represents the first amino acid and the right end (C-terminal) the last amino acid. A protein thread is not an extended rigid rod — it folds and coils (secondary/tertiary structure).

Solution: Both statements are correct. The tertiary structure gives the 3-D shape essential for biological activity, and (as stated in NCERT) the glycosidic bond forms between carbon atoms of two adjacent monosaccharide units.

Solution: Both statements are correct. Energy released in catabolic (breakdown) reactions is trapped and stored as chemical bond energy in ATP, and living organisms work continuously and hence cannot afford to reach equilibrium.

Solution: Positional information (sequence) is the primary structure (i); the hollow woollen ball appearance is the tertiary-looking fold described as secondary structure (ii); subunits together form the quaternary structure (iv); the folding that forms the active site is the tertiary structure (iii). Hence a-i, b-ii, c-iv, d-iii.

Solution: In the primary structure, a protein is a linear polypeptide chain in which successive amino acids are joined together by peptide bonds; hence primary proteins are called polypeptides.

Solution: The Ramachandran plot (phi vs psi dihedral angles) is used to validate and confirm the allowed conformations of the polypeptide backbone, i.e. the structure of proteins.

Solution: In the primary structure (linear sequence) of a protein, the first amino acid is the N-terminal (amino end) and the last is the C-terminal (carboxyl end), giving two ends.

Solution: The statement reverses the facts: collagen is the most abundant protein in the animal world, while RuBisCO is the most abundant protein in the whole biosphere.

Solution: At the isoelectric point the positive and negative charges balance, so the protein carries no net charge.

Solution: Alpha helices and beta-pleated sheets are regular folding patterns of the polypeptide backbone and represent the secondary structure of proteins.

Solution: Quaternary structure arises from the assembly of two or more polypeptide chains (subunits) into a functional protein.

Solution: Protein tertiary structure is stabilized by hydrophobic interactions, hydrogen bonds, electrostatic (ionic) interactions and disulfide bonds. Ester bonds are not typical stabilizing interactions in protein folding.

Solution: Lipids are not true polymers/macromolecules; proteins, polysaccharides and nucleic acids are polymeric biomacromolecules.