Q.70 Match List I with List II
| LIST I | LIST II |
|---|---|
| A. Leucine B. Serine C. Glutamate D. Tryptophan | I. Phosphorylated by kinase II. Negatively charged R group III. Non-polar, Aliphatic R group IV. Aromatic R group |
Choose the correct answer from the options given below:
- (A)–(III); (B)–(I); (C)–(IV); (D)–(II)
- (A)–(I); (B)–(II); (C)–(III); (D)–(IV)
- (A)–(III); (B)–(II); (C)–(IV); (D)–(I)
- (A)–(III); (B)–(I); (C)–(II); (D)–(IV)
Leucine has a non-polar aliphatic R group, serine is phosphorylated by kinase, glutamate has a negatively charged R group, and tryptophan has an aromatic R group. The correct option is (D): (A)–(III); (B)–(I); (C)–(II); (D)–(IV).
Question Breakdown
This matching question assesses amino acid classification by R-group properties, a core topic in biochemistry for exams like NEET/GATE Life Sciences.
Individual Matches
A. Leucine → III. Non-polar, Aliphatic R group
Leucine’s R group is -CH₂-CH(CH₃)₂, a branched hydrocarbon chain—hydrophobic and aliphatic.
B. Serine → I. Phosphorylated by kinase
Serine’s -CH₂OH side chain contains a hydroxyl group, a prime target for phosphorylation in signaling pathways.
C. Glutamate → II. Negatively charged R group
Glutamate’s R group is -CH₂-CH₂-COO⁻, acidic and negatively charged at physiological pH.
D. Tryptophan → IV. Aromatic R group
Tryptophan’s indole ring makes its R group aromatic and hydrophobic.Option Evaluation
Option A-Leu B-Ser C-Glu D-Trp Validity Reason First III I IV II False C (Glu ≠ Aromatic); D (Trp ≠ Negative). Second I II III IV False A (Leu ≠ Phosphorylated); B (Ser ≠ Negative). Third III II IV I False B (Ser ≠ Negative); C (Glu ≠ Aromatic). Fourth III I II IV True All matches align with R-group chemistry. Amino acid R group properties like non-polar aliphatic (leucine), phosphorylated by kinase (serine), negatively charged (glutamate), and aromatic (tryptophan) are essential for protein structure questions in competitive exams.
R Group Properties Table
Amino Acid R Group Structure Key Property Biological Role Leucine (A) -CH₂-CH(CH₃)₂ Non-polar, Aliphatic Hydrophobic core in proteins Serine (B) -CH₂OH Phosphorylated by kinase Phosphorylation sites Glutamate (C) -CH₂-CH₂-COO⁻ Negatively charged Acidic, metal binding Tryptophan (D) Indole ring Aromatic UV absorbance, stacking Exam Tips
Focus on side chain chemistry: aliphatic = hydrocarbon chains; aromatic = rings; charged = ionizable groups; phosphorylatable = -OH/-Ser/Thr/Tyr. Common trap: Confusing polar uncharged serine with charged glutamate.
