Chemical foundations of cell biology – basic reactions and types MCQs With Answer provides B.Pharm students a concise, focused review of essential chemical principles that drive cellular processes. This introduction covers biomolecules, enzyme-catalyzed reactions, thermodynamics, acid–base and buffer chemistry, redox and phosphorylation, noncovalent interactions, and reaction classifications such as hydrolysis, condensation, isomerization and ligation. Emphasis on keywords like enzymes, metabolism, ATP hydrolysis, Henderson–Hasselbalch, pKa, Km, coenzymes (NAD+, FAD), and buffer systems prepares you for applied pharmaceutical contexts. Clear mechanistic concepts and problem-style MCQs sharpen analytical skills needed for drug action and formulation. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which bond formation occurs during peptide synthesis between amino acids?
- Glycosidic bond
- Peptide (amide) bond
- Phosphodiester bond
- Disulfide bond
Correct Answer: Peptide (amide) bond
Q2. The Henderson–Hasselbalch equation is used to relate pH to which pair of quantities?
- ΔG° and Keq
- pKa and ratio of conjugate base to acid
- Km and Vmax
- Redox potential and electron number
Correct Answer: pKa and ratio of conjugate base to acid
Q3. Which interaction primarily drives protein folding by excluding water from nonpolar surfaces?
- Hydrogen bonding
- Ionic bonds
- Hydrophobic effect
- Disulfide bonding
Correct Answer: Hydrophobic effect
Q4. In Michaelis–Menten kinetics, what does a low Km value indicate about an enzyme-substrate interaction?
- Low catalytic efficiency
- High substrate affinity
- High Vmax
- Competitive inhibition
Correct Answer: High substrate affinity
Q5. Which coenzyme commonly accepts hydride ions in cellular oxidation reactions?
- Coenzyme A (CoA)
- NAD+
- Biotin
- ATP
Correct Answer: NAD+
Q6. Hydrolysis of ATP to ADP + Pi under standard cellular conditions is best described as:
- Endergonic and nonspontaneous
- Exergonic and releases free energy
- At equilibrium with ΔG = 0
- An oxidation reaction only
Correct Answer: Exergonic and releases free energy
Q7. Which type of reaction converts a monosaccharide into its structural isomer (e.g., glucose to fructose)?
- Oxidation–reduction
- Isomerization
- Hydrolysis
- Condensation
Correct Answer: Isomerization
Q8. For a buffer composed of a weak acid (HA) and its conjugate base (A-), maximal buffering capacity occurs when:
- pH = pKa of HA
- pH is far below pKa
- pH is far above pKa
- pH = 7.0 only
Correct Answer: pH = pKa of HA
Q9. Which statement is true about noncompetitive enzyme inhibitors?
- They increase Km but do not change Vmax
- They bind only to the active site
- They decrease Vmax without changing Km
- They are always reversible by substrate excess
Correct Answer: They decrease Vmax without changing Km
Q10. The standard free energy change ΔG° is related to the equilibrium constant Keq by which expression?
- ΔG° = RT ln(Vmax)
- ΔG° = -RT ln Keq
- ΔG° = Km / Vmax
- ΔG° = pH × pKa
Correct Answer: ΔG° = -RT ln Keq
Q11. Which bond is formed between nucleotides in RNA and DNA backbones?
- Glycosidic bond
- Peptide bond
- Phosphodiester bond
- Hydrogen bond
Correct Answer: Phosphodiester bond
Q12. A reaction with a negative ΔG under cellular conditions is best described as:
- Endergonic
- Nonspontaneous
- Spontaneous and thermodynamically favorable
- At equilibrium
Correct Answer: Spontaneous and thermodynamically favorable
Q13. Which type of chemical reaction connects two molecules with the loss of water?
- Hydrolysis
- Condensation (dehydration synthesis)
- Oxidation
- Isomerization
Correct Answer: Condensation (dehydration synthesis)
Q14. The isoelectric point (pI) of a protein is defined as the pH at which:
- The net charge of the protein is zero
- The protein is maximally soluble
- The protein has the most negative charge
- All acidic side chains are fully deprotonated
Correct Answer: The net charge of the protein is zero
Q15. Which interaction is primarily responsible for base pairing specificity in DNA?
- Ionic bonds between phosphates
- Covalent glycosidic bonds
- Hydrogen bonds between bases
- Hydrophobic interactions among sugars
Correct Answer: Hydrogen bonds between bases
Q16. In an oxidation–reduction (redox) reaction, the species that loses electrons is:
- Reduced
- Oxidized
- Always a coenzyme
- Unchanged
Correct Answer: Oxidized
Q17. Which physiological buffer system is most important for short-term regulation of blood pH?
- Hemoglobin buffer
- Bicarbonate (HCO3-/CO2) buffer
- Phosphate buffer only
- Protein denaturation
Correct Answer: Bicarbonate (HCO3-/CO2) buffer
Q18. A catalyst accelerates a chemical reaction primarily by:
- Lowering the activation energy of the reaction
- Changing ΔG° of the reaction
- Increasing the equilibrium constant
- Converting reactants into different products
Correct Answer: Lowering the activation energy of the reaction
Q19. Which amino acid side chain can form covalent disulfide bonds stabilizing tertiary structure?
- Methionine
- Cysteine
- Serine
- Alanine
Correct Answer: Cysteine
Q20. Which quantity describes how much product is formed per unit time by an enzyme at saturating substrate?
- Km
- Vmax
- kcat (turnover number)
- ΔG
Correct Answer: Vmax
Q21. In acid–base titration of a weak acid, the midpoint of the titration (half-neutralization) corresponds to:
- pH = 7.0 always
- pH = pKa of the acid
- Maximum slope of the titration curve
- Complete neutralization
Correct Answer: pH = pKa of the acid
Q22. Which type of reaction transfers a phosphoryl group between molecules?
- Ligation
- Phosphorylation (transferase-catalyzed)
- Reductive amination
- Hydrolysis only
Correct Answer: Phosphorylation (transferase-catalyzed)
Q23. The term “activation energy” refers to:
- The energy difference between products and reactants at equilibrium
- The energy barrier that must be overcome for reactants to form products
- The total thermal energy of the solution
- The energy released by ATP hydrolysis
Correct Answer: The energy barrier that must be overcome for reactants to form products
Q24. Which property of water most strongly contributes to its role as a universal solvent in cells?
- High viscosity
- High dielectric constant and polarity
- Low specific heat
- Nonpolarity
Correct Answer: High dielectric constant and polarity
Q25. In a redox pair, the compound with the higher (more positive) reduction potential is more likely to:
- Donate electrons (be oxidized)
- Accept electrons (be reduced)
- Be inert
- Act as a buffer
Correct Answer: Accept electrons (be reduced)
Q26. Which reaction type is catalyzed by proteases in the digestion of proteins?
- Condensation
- Hydrolysis of peptide bonds
- Oxidative phosphorylation
- Isomerization
Correct Answer: Hydrolysis of peptide bonds
Q27. The Michaelis constant Km approximates which concentration in simple enzyme mechanisms?
- Substrate concentration at which reaction rate is half of Vmax
- Maximum rate of reaction
- Inhibitor concentration for half-maximal inhibition
- Product concentration at equilibrium
Correct Answer: Substrate concentration at which reaction rate is half of Vmax
Q28. Which noncovalent force is strongest under physiological conditions and often directs salt bridge formation?
- Van der Waals forces
- Ionic (electrostatic) interactions
- London dispersion only
- Pi stacking exclusively
Correct Answer: Ionic (electrostatic) interactions
Q29. Coupling an endergonic biosynthetic reaction to ATP hydrolysis is effective because ATP hydrolysis:
- Is endergonic and drives equilibrium toward reactants
- Provides a large negative ΔG to drive the coupled reaction
- Always increases pH of the medium
- Inhibits enzymes noncompetitively
Correct Answer: Provides a large negative ΔG to drive the coupled reaction
Q30. Which statement best characterizes the hydrophobic effect in membranes and protein cores?
- Hydrophobic molecules form strong covalent bonds with water
- Ordering of water around nonpolar groups is entropically unfavorable, so nonpolar groups aggregate to release water
- Hydrophobic effect is identical to ionic bonding
- It refers to attraction between charged residues only
Correct Answer: Ordering of water around nonpolar groups is entropically unfavorable, so nonpolar groups aggregate to release water
