Charge of peptides and proteins

Question 1

Isoelectric point

Answer 1

pI is the pH at which the molecule carries no electric charge
pI=1/2(pKai +pKaj)
Kai and Kaj are the pKas of the two ionisations
Glycine= pKa1 pKa2
Aspartic and glutamic acids= pKa1 pKaR
Arginine, histidine, lysine = pKaR pKa2

Question 2

Buffers

Answer 2

The higher the concentration of a buffer the more OH- ( or H+) is required to change the pH in the range of the buffer.

Question 3

Charge on proteins

Answer 3

Help bind to other proteins or molecules
Different charges can be used to separate and purify them by electrophoresis
Different charges on proteins can be used to separate and purify them by ion exchange chromatography