Chemistry - Biomolecules Question with Solution | TestHub
Amino acids contain as —NH2 as well as —COOH group. They exist as zwitter ions.
Which explain their several characteristic properties, like decomposition on heating, solubility in water, larger dipole moment. Thus in solution, amino acids may exist as dipolar ion (neutral pH), cationic (In strongly acidic solution), or anionic (in strongly basic solution).
Amino acids undergo usual reaction of the —COOH group as well as —NH2 group
At intracellular , amino acids can be divided into four types positively charged, negatively charged, hydrophobic and hydrophilic. Which is the correct classification of the following four amino acids?
Options:
Answer:
Solution:
Question Explanation:
Classify amino acids at intracellular pH (~6–7) based on their side chain properties into positively charged, negatively charged, hydrophobic, or hydrophilic.
Concept :
This question is based on Amino acid classification, Zwitterion, Side chain properties. Solution:
C6H5–CH2–CH(NH3+)–COO- (Phenylalanine)
Side chain: non-polar benzyl group
No ionisable group in side chain at pH 6–7
Classification: Hydrophobic (neutral)
C6H5–CH(OH)–CH(NH3+)–COO- (Tyrosine)
Side chain contains phenolic –OH (polar but uncharged at pH 6–7)
Can form hydrogen bonds with water
Classification: Hydrophilic (neutral)
H3N+–(CH2)4–CH(NH3+)–COO- (Lysine)
Side chain has an extra amino group (pK ≈ 10.5)
Protonated at pH 6–7
Classification: Positively charged (basic)
-OOC–CH2–CH(NH3+ )–COO- (Aspartic acid)
Side chain contains an extra carboxyl group (pK ≈ 3.9)
Deprotonated at pH 6–7
Classification: Negatively charged (acidic)
Final answer : Option (B)
