Biomolecules and Chemistry in Everyday Life 1 Question 12
13. The correct sequence of amino acids present in the tripeptide given below is
(2019 Main, 9 Jan II)
(a) Thr - Ser - Leu
(b) Leu - Ser - Thr
(c) Val - Ser - Thr
(d) Thr - Ser - Val
14 The increasing order of $p K_{a}$ of the following amino acids in] aqueous solution is Gly, Asp, Lys, Arg
(2019 Main, 9 Jan I)
(a) Asp $<$ Gly $<$ Arg $<$ Lys
(b) Arg $<$ Lys $<$ Gly $<$ Asp
(c) Gly $<$ Asp $<$ Arg $<$ Lys
(d) Asp $<$ Gly $<$ Lys $<$ Arg
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Solution:
- Formation of the tripeptide (Val-Ser-Thr) can be shown as:
14 Amino acid molecules can be represented as,
Nature of the ’ $R$ ’ group will determine the basicity (hence, $\mathrm{p} K_{a}$ ) of an amino acid.
| ’ $R$ ’ in the amino group | Nature of $R$ |
Nature of the amino acids |
|
|---|---|---|---|
| 1. | $-\left(\mathrm{CH}{2}\right){3}-\mathrm{NH}-\mathrm{C} / \stackrel{+}{N}{\mathrm{NH}{2}}^{\text {(Arginine : Arg) }}$ (Argin |
Basic | More basic (due to the presence of acetamidine group) |
| 2. | $-\mathrm{CH}{2}-\mathrm{C}{\mathrm{O}^{-}}^{/ / \mathrm{O}}$ (Aspartic acid: Asp) |
Acidic | Acidic |
| 3. | —H (Glycine) : Gly | Neutral | Neutral |
| 4. | $-\left(\mathrm{CH}{2}\right){4}-\stackrel{+}{\mathrm{N}} \mathrm{H}_{3}$ (Lysine : Lys) |
Basic | Basic |
