The one that does not stabilize $2^{\circ}$ and $3^{\circ}$ structures of proteins is

What is the monomer of a polypeptide?

The correct match between Item $I$ and Item $II$ is

Item $I$	Item $II$
$A$. Ester test	$P$. Tyr
$B$. Carbylamine test	$Q$. Asp
$C$. Phthalein dye test	$R$. Ser
	$S$. Lys

Consider the following sequence for aspartic acid:
$H_3N^+-CH(COOH)-CH_2COOH \leftrightarrow{pK_1=1.88} H_3N^+-CH(COO^-)-CH_2COOH \leftrightarrow{pK_R=3.65} H_3N^+-CH(COO^-)-CH_2COO^- \leftrightarrow{pK_2=9.60} H_2N-CH(COO^-)-CH_2COO^-$
The $pI$ (isoelectric point) of aspartic acid is:

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

Which of the following is a Zwitter ion?