amino acids 9/12

Question 1

what is the usual pattern of amino acid charge difference with amino acids with 2 P_k’s

Answer 1

+1 –> zwitterion –> -1

Question 2

what amino acids have unique charge difference patterns and a P_kR

Answer 2

cysteine, tyrosine, lysine, arginine, histidine, aspartate, glutamate

Question 3

how is the isoelectric pH determined

Answer 3

pK₁ + pK₂/2 (two pK’s in middle of zwitterion)

Question 4

as pH goes from low to high what happens to the charge of the amino acid

Answer 4

positive to negative

Question 5

what should the pH of the elution buffer be for cation exchange chromatography

Answer 5

above pKa of stationary phase and close to the pKa of samples

Question 6

You are doing cation exchange chromatography. The samples take a long time to elute and then all come out together. How do you fix this?

Answer 6

raise pH of elution buffer

Question 7

what pKa’s do you look at for cation and anion chromatography?

Answer 7

cation: pK₂ and pK_R
anion: pK₁

Question 8

in both a cation and anion column what pKa will cause slower movement?

Answer 8

cation: high pKa slowest
anion: low pKa slowest