Which of the following is an example of a sulphur-containing amino acid?

The structure of a peptide is given below. If the absolute values of the net charge of the peptide at $pH = 2$,$pH = 6$,and $pH = 11$ are $|z_1|$,$|z_2|$,and $|z_3|$,respectively,then what is $|z_1| + |z_2| + |z_3|$?

What is the relationship between the isoelectric point and the solubility of amino acids?

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:

Which of the following is manufactured from molecular nitrogen by bacteria?

The correct sequence of amino acids present in the tripeptide given below is