UBC BIOL 201 REAL QUESTIONS + DETAILED ANSWERS -
LATEST VERSION - TOP RATED 2026/2027
Q1. What is the Henderson-Hasselbalch equation? ANSWER pH = pKa +
log([A⁻]/[HA])
Q2. What does pKa represent? ANSWER The pH at which half of the
ionizable group is in its protonated form and half is in its deprotonated form; it
equals −log(Ka).
Q3. When pH > pKa, what is the predominant form of a weak acid? ANSWER
The deprotonated (conjugate base, A⁻) form predominates.
Q4. When pH < pKa, what is the predominant form of a weak acid? ANSWER
The protonated (acid, HA) form predominates.
Q5. What is the pKa of a carboxylic acid group (–COOH)? ANSWER
Approximately 2–4 (typically ~2 for α-carboxyl groups on amino acids).
Q6. What is the pKa of an amino group (–NH₃⁺)? ANSWER Approximately
9–10 (typically ~9 for α-amino groups on amino acids).
Q7. What are the four main types of ionizable functional groups found in
biological molecules? ANSWER Carboxylic acids (–COOH), amines (–NH₃⁺),
phosphate groups, and thiols (–SH, e.g., in cysteine).
Q8. At physiological pH (7.4), what is the predominant form of a carboxylic
acid group (pKa ~2)? ANSWER The deprotonated form (–COO⁻).
Q9. What is a buffer? ANSWER A solution that resists changes in pH upon
addition of small amounts of acid or base; it consists of a weak acid and its
conjugate base.
Q10. What is the buffering range of a weak acid/base pair? ANSWER
Approximately pH = pKa ± 1.
Q11. Why is the phosphate buffer system important physiologically?
ANSWER It has a pKa of ~7.2, which is close to physiological pH (~7.4),
making it effective at buffering intracellular fluids.
,Q12. What is the pKa of the imidazole side chain of histidine? ANSWER
~6.0, making histidine uniquely able to act as a proton donor/acceptor near
physiological pH.
Q13. What happens to the net charge of an amino acid at its isoelectric point
(pI)? ANSWER The net charge is zero.
Q14. How is pI calculated for a simple amino acid with one α-amino and one α-
carboxyl group? ANSWER pI = (pKa1 + pKa2) / 2, where pKa1 and pKa2 are
the pKa values of the two ionizable groups.
Q15. What does "predominant species" mean in the context of ionization?
ANSWER The form of a molecule (protonated or deprotonated at each
ionizable group) that is most abundant at a given pH.
Q16. What is the Ka expression for a weak acid HA? ANSWER Ka =
[H⁺][A⁻] / [HA]
Q17. A molecule has two ionizable groups with pKa values of 4 and 9. At pH 7,
what is the predominant species? ANSWER The carboxyl group (pKa 4) is
deprotonated (–COO⁻) and the amine group (pKa 9) is protonated (–NH₃⁺); net
charge = 0.
Q18. What is the significance of water's high dielectric constant for biological
molecules? ANSWER It reduces electrostatic interactions between charged
molecules, stabilizing ions and polar solutes in aqueous solution.
Q19. What types of weak interactions stabilize biological macromolecules in
aqueous solution? ANSWER Hydrogen bonds, hydrophobic interactions, van
der Waals forces, and ionic (electrostatic) interactions.
Q20. Why do hydrophobic molecules aggregate in water? ANSWER Their
aggregation minimizes the entropy cost of organizing water molecules around
nonpolar surfaces (hydrophobic effect).
UNIT 2 ANSWER Amino Acids
Q21. What are the four groups attached to the α-carbon of a standard amino
acid? ANSWER An amino group (–NH₃⁺), a carboxyl group (–COO⁻), a
hydrogen atom, and a variable R (side chain) group.
Q22. How many standard amino acids are there? ANSWER 20.
, Q23. All standard amino acids (except glycine) are L-amino acids. What does
this mean? ANSWER Their absolute configuration matches the L-
stereoisomer based on the relationship of groups around the chiral α-carbon.
Q24. Which amino acid has no chiral center? ANSWER Glycine (its R group
is –H, so both substituents on the α-carbon are the same).
Q25. Name the nonpolar, aliphatic amino acids. ANSWER Glycine (Gly),
Alanine (Ala), Valine (Val), Leucine (Leu), Isoleucine (Ile), Proline (Pro),
Methionine (Met).
Q26. Name the aromatic amino acids. ANSWER Phenylalanine (Phe),
Tyrosine (Tyr), Tryptophan (Trp).
Q27. Which aromatic amino acids absorb UV light at 280 nm? ANSWER
Tyrosine and Tryptophan (Phenylalanine absorbs weakly at 257 nm).
Q28. Name the polar, uncharged amino acids at pH 7. ANSWER Serine (Ser),
Threonine (Thr), Cysteine (Cys), Asparagine (Asn), Glutamine (Gln), Tyrosine
(Tyr).
Q29. Name the negatively charged (acidic) amino acids at pH 7. ANSWER
Aspartate (Asp) and Glutamate (Glu).
Q30. Name the positively charged (basic) amino acids at pH 7. ANSWER
Lysine (Lys), Arginine (Arg), Histidine (His).
Q31. Which amino acid has a side chain that can form disulfide bonds?
ANSWER Cysteine (–SH groups from two cysteines oxidize to form –S–S–).
Q32. Which amino acid's side chain pKa (~6.0) allows it to function as an
acid/base catalyst at physiological pH? ANSWER Histidine.
Q33. What is special about proline's structure? ANSWER Its side chain forms
a ring back to the nitrogen, making it a secondary amine (imino acid); it
introduces rigidity and kinks in polypeptide chains.
Q34. What are the one-letter and three-letter codes for tryptophan? ANSWER
W; Trp.
Q35. What type of bond connects amino acids in a polypeptide? ANSWER A
peptide (amide) bond, formed between the α-carboxyl group of one amino acid
and the α-amino group of the next, with loss of water.
Q36. What is the N-terminus of a polypeptide? ANSWER The end with a free
α-amino group (–NH₃⁺); it is written on the left by convention.
LATEST VERSION - TOP RATED 2026/2027
Q1. What is the Henderson-Hasselbalch equation? ANSWER pH = pKa +
log([A⁻]/[HA])
Q2. What does pKa represent? ANSWER The pH at which half of the
ionizable group is in its protonated form and half is in its deprotonated form; it
equals −log(Ka).
Q3. When pH > pKa, what is the predominant form of a weak acid? ANSWER
The deprotonated (conjugate base, A⁻) form predominates.
Q4. When pH < pKa, what is the predominant form of a weak acid? ANSWER
The protonated (acid, HA) form predominates.
Q5. What is the pKa of a carboxylic acid group (–COOH)? ANSWER
Approximately 2–4 (typically ~2 for α-carboxyl groups on amino acids).
Q6. What is the pKa of an amino group (–NH₃⁺)? ANSWER Approximately
9–10 (typically ~9 for α-amino groups on amino acids).
Q7. What are the four main types of ionizable functional groups found in
biological molecules? ANSWER Carboxylic acids (–COOH), amines (–NH₃⁺),
phosphate groups, and thiols (–SH, e.g., in cysteine).
Q8. At physiological pH (7.4), what is the predominant form of a carboxylic
acid group (pKa ~2)? ANSWER The deprotonated form (–COO⁻).
Q9. What is a buffer? ANSWER A solution that resists changes in pH upon
addition of small amounts of acid or base; it consists of a weak acid and its
conjugate base.
Q10. What is the buffering range of a weak acid/base pair? ANSWER
Approximately pH = pKa ± 1.
Q11. Why is the phosphate buffer system important physiologically?
ANSWER It has a pKa of ~7.2, which is close to physiological pH (~7.4),
making it effective at buffering intracellular fluids.
,Q12. What is the pKa of the imidazole side chain of histidine? ANSWER
~6.0, making histidine uniquely able to act as a proton donor/acceptor near
physiological pH.
Q13. What happens to the net charge of an amino acid at its isoelectric point
(pI)? ANSWER The net charge is zero.
Q14. How is pI calculated for a simple amino acid with one α-amino and one α-
carboxyl group? ANSWER pI = (pKa1 + pKa2) / 2, where pKa1 and pKa2 are
the pKa values of the two ionizable groups.
Q15. What does "predominant species" mean in the context of ionization?
ANSWER The form of a molecule (protonated or deprotonated at each
ionizable group) that is most abundant at a given pH.
Q16. What is the Ka expression for a weak acid HA? ANSWER Ka =
[H⁺][A⁻] / [HA]
Q17. A molecule has two ionizable groups with pKa values of 4 and 9. At pH 7,
what is the predominant species? ANSWER The carboxyl group (pKa 4) is
deprotonated (–COO⁻) and the amine group (pKa 9) is protonated (–NH₃⁺); net
charge = 0.
Q18. What is the significance of water's high dielectric constant for biological
molecules? ANSWER It reduces electrostatic interactions between charged
molecules, stabilizing ions and polar solutes in aqueous solution.
Q19. What types of weak interactions stabilize biological macromolecules in
aqueous solution? ANSWER Hydrogen bonds, hydrophobic interactions, van
der Waals forces, and ionic (electrostatic) interactions.
Q20. Why do hydrophobic molecules aggregate in water? ANSWER Their
aggregation minimizes the entropy cost of organizing water molecules around
nonpolar surfaces (hydrophobic effect).
UNIT 2 ANSWER Amino Acids
Q21. What are the four groups attached to the α-carbon of a standard amino
acid? ANSWER An amino group (–NH₃⁺), a carboxyl group (–COO⁻), a
hydrogen atom, and a variable R (side chain) group.
Q22. How many standard amino acids are there? ANSWER 20.
, Q23. All standard amino acids (except glycine) are L-amino acids. What does
this mean? ANSWER Their absolute configuration matches the L-
stereoisomer based on the relationship of groups around the chiral α-carbon.
Q24. Which amino acid has no chiral center? ANSWER Glycine (its R group
is –H, so both substituents on the α-carbon are the same).
Q25. Name the nonpolar, aliphatic amino acids. ANSWER Glycine (Gly),
Alanine (Ala), Valine (Val), Leucine (Leu), Isoleucine (Ile), Proline (Pro),
Methionine (Met).
Q26. Name the aromatic amino acids. ANSWER Phenylalanine (Phe),
Tyrosine (Tyr), Tryptophan (Trp).
Q27. Which aromatic amino acids absorb UV light at 280 nm? ANSWER
Tyrosine and Tryptophan (Phenylalanine absorbs weakly at 257 nm).
Q28. Name the polar, uncharged amino acids at pH 7. ANSWER Serine (Ser),
Threonine (Thr), Cysteine (Cys), Asparagine (Asn), Glutamine (Gln), Tyrosine
(Tyr).
Q29. Name the negatively charged (acidic) amino acids at pH 7. ANSWER
Aspartate (Asp) and Glutamate (Glu).
Q30. Name the positively charged (basic) amino acids at pH 7. ANSWER
Lysine (Lys), Arginine (Arg), Histidine (His).
Q31. Which amino acid has a side chain that can form disulfide bonds?
ANSWER Cysteine (–SH groups from two cysteines oxidize to form –S–S–).
Q32. Which amino acid's side chain pKa (~6.0) allows it to function as an
acid/base catalyst at physiological pH? ANSWER Histidine.
Q33. What is special about proline's structure? ANSWER Its side chain forms
a ring back to the nitrogen, making it a secondary amine (imino acid); it
introduces rigidity and kinks in polypeptide chains.
Q34. What are the one-letter and three-letter codes for tryptophan? ANSWER
W; Trp.
Q35. What type of bond connects amino acids in a polypeptide? ANSWER A
peptide (amide) bond, formed between the α-carboxyl group of one amino acid
and the α-amino group of the next, with loss of water.
Q36. What is the N-terminus of a polypeptide? ANSWER The end with a free
α-amino group (–NH₃⁺); it is written on the left by convention.
