L7 General Properties and pH

Question 1

What is an enzyme?

Answer 1

• enhances the rate of chemical reactions
• doesn’t alter the equilibrium of reactions
• Reduces the energy barrier to the forward and reverse steps

Question 2

What is the dissociation constant, ka formula?

Answer 2

([H+][A-])/
[HA]

Question 3

How do you calculate pKa from ka

Answer 3

pKa = - log Ka

Question 4

As pH increases, why do amino acids become deprotonated?

Answer 4

As pH increases, the concentration of hydroxide ions (OH-) increases. These hydroxide ions can readily accept protons from the amino and carboxylate round of amino acids.

Carboxylate group donates proton, forming a carboxylate ion

Question 5

What does pka and ka stand for?

Answer 5

Ka stands for acid dissociation constant so it means how readily it is to dissociate into its conjugate base and a hydrogen ion. HA 🔄 H+ + A-
Higher Ka = stronger acid

pKa is the negative logarithm of Ka so lower pKa value indicates a stronger acid

Question 6

Are enzyme catalyzed reactions pH sensitive?

Answer 6

Yes, they are pH sensitive.

Chymotrypsin optimal pH is at 8 whereas pepsin’s optimal pH is 2

Question 7

What is usually responsible for pH dependent reaction profiles?

Answer 7

The protonation state of the side chain of a residue is usually responsible

Question 8

Do side chains deprotonated or protonate at high pH’s?

Answer 8

Side chains love to deprotonate. To maintain equilibrium, the ionizable groups like COOH tend to donate protons to the hydroxide ions