AA's Acid base chemistry

Question 1

pKa of a group

Answer 1

the pH at which on average 1/2 of the molecules of that species are deprotonated

pH at which [HA] =[A-]

Question 2

pH < pKa

pKa is greater than the pH

Answer 2

a majority of the species will be protonated

Question 3

pH> pKa

pH is greater than the pH

Answer 3

a majority of the species will be deprotonated

Question 4

minimum how many groups in AA can be deprotonated

Answer 4

2, hence 2 pKa values

Question 5

pKa of carbonyl group

Answer 5

~2

Question 6

pKa of Amino group

Answer 6

~ 9-10

Question 7

1. AA’s charge under acidic condition
2. AA’s Charge in intermeditae pH
3. AA’s charge under basic condition

Answer 7

1. • (Amino group and COOH group fully protonated NH3+ and COOH)
2. Zwitterions (hybrid) [NH3 +, COO -]
3. negative (both NH2 and COOH group will be deprotonated)

Question 8

pI isoelectric point

Answer 8

pH at which the molecule is electrically neutral

Question 9

pI for neutral AA

Answer 9

pKa (of NH3+ group) + pKa (of COOh group) / 2

Question 10

pI of an acidic AA

Answer 10

pKa (of the R group) + pKa (of the COOH group) /2

AA w/ acidic side chain have pI values <6

Question 11

pI of a basic AA

Answer 11

pKa (NH3+ group) + pKa (of the R group) /2

AA w/ basic side chain have pI values >6