pH pKa

Question 1

When pH = pKa

Answer 1

the charged group will be 50% ionised.

Question 2

pH > pKa

Answer 2

Mostly in conjugate base form (lost H+, wants to gain)

Question 3

pH < pKa

Answer 3

Mostly in conjugate acid ( gained H+, have proton to donate)

Question 4

What is pI?

Answer 4

pI of the protein is the pH at which its net charge is zero.

Question 5

What must have for catalyse to happen?

Answer 5

Proton donor - protonated ( have proton to donate)

Question 6

What are the pKa shifting mechanisms?

Answer 6

Charge-Charge interactions, Charge-dipole interaction, Burying charge in a hydrophobic environment.

Question 7

What are charge-charge interactions?

Answer 7

• Two like charges in close proximity
• Two opposite charges in close proximity
• Effect increased in a hydrophobic environment

Question 8

What are charge-dipole interactions?

Answer 8

• Interaction with dipole via H-bonding

- Interaction with alpha-helix dipole

Question 9

In charge-charge interactions, what will happen when negatively charged groups are brought together?

Answer 9

The pKa of one of -VE group will INCREASE to reduce the repulsion of like charges.

Question 10

In charge-charge interactions, what will happen when positively charged groups are brought together?

Answer 10

The pKa of one of the +VE group will REDUCE.

Question 11

In charge-charge interactions, what will happen when the opposite charged group are brought together?

Answer 11

The pKa of NEGATIVELY charged group will DECREASE or the POSITIVELY charged will INCREASE to promote favourable charged interactions.