In: Chemistry
Calculate to 3 decimal places the charge on a-melanotropin at pH values of 11, 5, and 1
please do not use titration curve explanation - i dont understand it and it wont help - i have the answers - i do not understand how to get them however - which values have negative and positive charges? and at what pHs? thats what confuses me.
TIA
Charges on proteins result from simple acid/base chemistry. Acidic and basic groups on the proteins lose/gain protons depending on the pH of the solution. The loss or gain of the proton will alter the charge of the protein. We should know which amino acids are acidic/basic and their pKa values (the pH at which they become protonated/deprotonated. Aspartate, glutamate, and cysteine are acidic and have a negative charge at high pH and a neutral charge at low pH (serine and threonine can also be considered in this group although they have a fairly high pKas). Lysine, arginine, and histinde are basic and have a neutral at high pH and have positive charge at low pH. You also need to take into account the effects of the amino group on the N-terminus of the peptide and the carboxyl group at the C-terminus of the peptide.
The charge on α-melanotropin at pH value of 11 is - 1.827
The charge on α-melanotropin at pH value of 5 is 2.104
The charge on α-melanotropin at pH value of 1 is 3.998