The total number of isomeric linear dipeptides which can be synthesised from racemic alanine is

Which of the following compounds will form a zwitterion?

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

Match List-$I$ with List-$II$.

List-$I$ (Natural amino acid)	List-$II$ (Code)
$A$. Glutamic acid	$I$. $Q$
$B$. Glutamine	$II$. $W$
$C$. Tyrosine	$III$. $E$
$D$. Tryptophan	$IV$. $Y$

Which one of the following amino acids has an isoelectric pH greater than $7$?

Which bond is responsible for the secondary structure of proteins?