Q8 / 180 · COMEDK 2021 · Chemistry
Which of the following amino acid $\left(\mathrm{NH}_{2} \mathrm{CH} R \mathrm{COOH}\right)$ contains polar $R$ group?
- AAlanine
- BValine
- CGlycine
- Correct answerDGlutamine
Solution
The structure of an amino acid is $\mathrm{NH}_{2}CH(R)\mathrm{COOH}$. The polarity of the $R$ group depends on the presence of functional groups capable of hydrogen bonding or having a dipole moment.
Alanine has $R = -\mathrm{CH}_{3}$, which is non-polar.
Valine has $R = -\mathrm{CH}(\mathrm{CH}_{3})_{2}$, which is non-polar.
Glycine has $R = -\mathrm{H}$, which is non-polar.
Glutamine has $R = -\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{CONH}_{2}$. The amide group ($-\mathrm{CONH}_{2}$) is polar due to the electronegative oxygen and nitrogen atoms, allowing it to participate in hydrogen bonding. Therefore, the $R$ group in glutamine is polar.
Answer: Glutamine
Alanine has $R = -\mathrm{CH}_{3}$, which is non-polar.
Valine has $R = -\mathrm{CH}(\mathrm{CH}_{3})_{2}$, which is non-polar.
Glycine has $R = -\mathrm{H}$, which is non-polar.
Glutamine has $R = -\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{CONH}_{2}$. The amide group ($-\mathrm{CONH}_{2}$) is polar due to the electronegative oxygen and nitrogen atoms, allowing it to participate in hydrogen bonding. Therefore, the $R$ group in glutamine is polar.
Answer: Glutamine
Hence, the correct answer is option: 'D'.