Kaplan Ch. 1 - Amino Acids, Peptides And Proteins

Question 1

What is the pka of COOH in AA?

What is the pka of NH2 in AA?

Answer 1

COOH = approx 2
NH2 = approx 9-10

Question 2

At physiologic pH, how will AAs be charged?

What about at very low pH = 1?
What about very high pH = 12?

Answer 2

At pH = 7.4:

COOH will act as acid (it’s pka is 2 vs physiologic 7.4) and donate H+ to solution. This it will exist in AA as COO-

NH2 will act as vase (it’s pka is 9-10 vs physiologic 7.4) and accept H+ from solution. Thus it will exist as NH3+

At pH =1:
NH3+ And COOH

At pH =12:
NH2 and COO-

Question 3

What is a zwitterion?

Answer 3

A diploar ion - when a molecule has both positive and negative charge but is overall electrically neutral.

Question 4

What is the isoeletric point?

Answer 4

The point at which the molecule is electrically neutral (NH3+ and COO- are present in equal amounts)

Question 5

In an AA without the possibility of having a charged side chain, how is the pI determined?

Answer 5

pI = pka (NH group) + pka (COOH group) / 2

Question 6

For an acidic amino acid, how is the pI calculated?

Answer 6

pI = ((pka COOH group) + (pka R group)) / 2

Question 7

For a basic amino acid, how is the pI determined?

Answer 7

pI = ((pka NH group) + (pka R group)) / 2

Question 8

What is the convention for writing and reading amino acid sequences?

Answer 8

N terminus on the left, c terminus on the right

Read from n terminus to c terminus

Question 9

What sort of reactions do lyases catalyze?

What is the reverse of a lyase called? What is it’s function?

Answer 9

Cleavage of single molecule into 2 new molecules, don’t use water

Reverse = synthase, same enzyme but named for the reverse reaction where it catalyzes the combination of 2 molecules into 1 molecule

Question 10

What sort of reactions do ligases catalyze?

Answer 10

Addition and synthesis reactions of large molecules that are generally similar (I.e. DNA Ligase)