Biomolecules MCQs

Which of the following statements regarding the building blocks of nucleic acids are correct?

I. A nucleotide consists of three chemically distinct components: a heterocyclic nitrogen base, a monosaccharide pentose sugar, and phosphoric acid.
II. Adenine and Guanine are substituted pyrimidines, whereas Cytosine, Uracil, and Thymine are substituted purines.
III. Nucleosides lack phosphate groups and consist of a nitrogenous base attached to a sugar (e.g., Adenosine, Uridine).
IV. DNA contains 2'-deoxyribose sugar, while RNA contains ribose sugar.

Which of the above statements are correct?

Which of the following statements regarding quaternary protein architecture and human haemoglobin are correct?

I. Quaternary structure represents the architectural arrangement of proteins composed of more than one polypeptide subunit.
II. Adult human haemoglobin consists of four subunits: two identical α-type subunits and two identical β-type subunits.
III. Individual subunits in a quaternary structure are arranged with respect to each other as a linear string of spheres or plates.
IV. Haemoglobin exhibits tertiary structure only, as all four polypeptide chains are fused into a single continuous peptide chain.

Which of the above statements are correct?

Which of the following statements regarding enzyme nature, active sites, and thermal stability are correct?

I. Almost all enzymes are proteins, but catalytic nucleic acids called ribozymes also exist.
II. An active site of an enzyme is a pocket or crevice created in its tertiary structure into which the substrate fits.
III. Inorganic catalysts work efficiently at high temperatures, whereas most enzymes get damaged above 40°C.
IV. Thermal stability is absent in thermophilic organisms, causing their enzymes to denature at 50°C.

Which of the above statements are correct?

Which of the following statements regarding the rate of enzymatic reactions and carbonic anhydrase acceleration are correct?

I. Rate of a physical or chemical process refers to the amount of product formed per unit time (δP/δt).
II. A general rule of thumb is that reaction rate doubles or decreases by half for every 10°C change in either direction.
III. Uncatalysed formation of carbonic acid (H2CO3) from CO2 and H2O produces about 200 molecules per hour.
IV. Carbonic anhydrase accelerates reaction rate by 10 million times, producing about 600,000 molecules per minute.

Which of the above statements are correct?

Which of the following statements regarding the transition state concept and activation energy are correct?

I. Substrate binding to the active site forms a transient enzyme-substrate (ES) complex.
II. During ES complex formation, the substrate structure is transformed into a high-energy transition state structure.
III. Activation energy is the difference in average energy content of substrate (S) from that of the transition state.
IV. Enzymes accelerate reaction rates by increasing the activation energy barrier between substrate and transition state.

Which of the above statements are correct?

Which of the following statements regarding potential energy profiles in reactions are correct?

I. If product (P) is at a lower potential energy level than substrate (S), the reaction is exothermic and spontaneous.
II. Endothermic reactions require energy input because S has to pass through a transition state, whereas exothermic reactions bypass the transition state entirely.
III. Both exothermic and endothermic reactions must proceed through a higher potential energy transition state.
IV. Intermediate structural states between substrate and product are unstable.

Which of the above statements are correct?

Which of the following statements regarding the catalytic cycle steps of enzyme action are correct?

I. Substrate binding to the active site induces the enzyme to alter its shape, fitting more tightly around the substrate.
II. The active site in close proximity breaks or forms chemical bonds, producing an enzyme-product (EP) complex.
III. The EP complex dissociates into free enzyme and product, allowing the enzyme to enter another catalytic cycle.
IV. During substrate binding, the enzyme undergoes permanent decomposition, requiring new synthesis for each reaction turn.

Which of the above statements are correct?

Which of the following statements regarding the factors affecting enzyme activity and substrate saturation are correct?

I. Enzymes show maximum activity at a specific optimum temperature and optimum pH, with activity declining both above and below these values.
II. Low temperature preserves enzymes in a temporarily inactive state, whereas high temperature destroys activity via protein denaturation.
III. Increasing substrate concentration continuously increases reaction velocity without limit.
IV. Substrate saturation occurs when all enzyme active sites are occupied, reaching maximum velocity (Vmax).

Which of the above statements are correct?

Which of the following statements regarding competitive inhibition and its applications are correct?

I. A competitive inhibitor closely resembles the substrate in molecular structure and competes for the active site binding pocket.
II. Inhibition of succinic dehydrogenase by malonate is a classic example of competitive inhibition.
III. Competitive inhibitors permanently alter the primary sequence of enzymes to double Vmax.
IV. Competitive inhibitors are used in controlling bacterial pathogens.

Which of the above statements are correct?

Which of the following statements regarding enzyme classification classes (EC 1 to EC 4) are correct?

I. Enzymes are divided into six classes, each with 4–13 subclasses, designated by a four-digit number.
II. Oxidoreductases (dehydrogenases) catalyze oxidation-reduction reactions between two substrates.
III. Hydrolases catalyze group transfer reactions (other than hydrogen) between a pair of substrates.
IV. Lyases catalyze removal of groups from substrates by mechanisms other than hydrolysis, leaving double bonds.

Which of the above statements are correct?