The correct representation of a nucleotide is:

Which is an optically inactive amino acid?

Among the $\alpha$-amino acids - threonine,tyrosine,methionine,arginine and tryptophan,those which contain an aromatic group in their side chain are

$1.$ Glycylglycine
$2.$ Alanylalanine
$3.$ Glycylalanine
$4.$ Alanylglycine
The dipeptides which may be obtained from the amino acids glycine and alanine are

Column-$I$	Column-$II$
$A$. Tyrosine	$P$. Essential amino acid
$B$. Serine	$Q$. Ceric Ammonium Nitrate
$C$. Tryptophan	$R$. Neutral $FeCl_{3}$
$D$. Proline	$S$. Carbylamine Test - Negative

Select the correct set of answer :

In an amino acid,the carboxylic group ionises at $pH = 2.56$ $(pK_{a_1})$ and the ammonium ion ionises at $pH = 9.38$ $(pK_{a_2})$. The isoelectric point of the amino acid is at: