Nitrogen is an essential constituent of all

The $\alpha-$helix and $\beta-$pleated sheet structures of protein are associated with its:

Which of the following amino acids is achiral?

The substituents $R_1$ and $R_2$ for nine peptides are listed in the table given below. How many of these peptides are positively charged at $pH = 7.0$?

Peptide	$R_1$	$R_2$
$I$	$H$	$H$
$II$	$H$	$CH_3$
$III$	$CH_2COOH$	$H$
$IV$	$CH_2CONH_2$	$(CH_2)_4NH_2$
$V$	$CH_2CONH_2$	$CH_2CONH_2$
$VI$	$(CH_2)_4NH_2$	$(CH_2)_4NH_2$
$VII$	$CH_2COOH$	$CH_2CONH_2$
$VIII$	$CH_2OH$	$(CH_2)_4NH_2$
$IX$	$(CH_2)_4NH_2$	$CH_3$

In an alkaline medium,glycine predominantly exists as/in a/an

Identify the amino acids obtained by hydrolysis of the following compound: $NH_2-CH(CH_3)-CO-NH-CH_2-COOH$