Proteins can be separated from small molecules and ions through a semipermeable membrane by __________________.

In the Edman procedure for peptide sequence, phenyl isothiocyanate is used to selectively remove the __________________ residue as a PTH-derivative.

Polypeptides can be fragmented into smaller peptides by cleavage with trypsin, which hydrolyzes the peptide bond at the C-terminal side of __________________ residues.