The test used for identifying peptide linkage in proteins is

Which amino acid does not contain a chiral center?

How many tripeptides can be prepared by linking the amino acids glycine,alanine and phenylalanine?

The $pK_a$ values for the three ionizable groups $X, Y$ and $Z$ of glutamic acid are $4.3, 9.7$ and $2.2$ respectively. The structure is $HO_2C-CH_2-CH_2-CH(NH_3^+)-CO_2H$. The isoelectric point $(pI)$ for this amino acid is:

Proteins are polymers of $\alpha$-amino acids,which are linked by peptide bonds. Chemically,proteins are:

Structures of alanine at $pH = 2$ and $pH = 10$ are respectively