Chapter 1: Amino Acids, Peptides, and Proteins

Question 1

Explain the difference between aspartic acid and asparagine.

Answer 1

aspartic acid has a hydroxyl group (OH) where asparagine has an amino group (NH2)

more???

Question 2

How is the direction of light rotation (clockwise vs anticlockwise) determined for a given amino acid?

Answer 2

experimentally

L vs D does not indicate the direction in which optically active molecules rotate light

Question 3

Which amino acid is NOT chiral?

Answer 3

glycine (it has 2 H groups on its alpha carbon)

Question 4

Are most chiral amino acids L or D? What is the exception?

stereochemistry

Answer 4

most amino acids are L-amino acids

exception: cysteine

Question 5

amphoteric meaning

Answer 5

can act as either an acid or a base

Question 6

pka meaning

Answer 6

the pH at which the species will lose its hydrogen ion

[HA] = [A-] (half of the molecules are deprotonated, half are protonated)

Question 7

zwitterion

Answer 7

a molecule with both a positive and negative charge, but is overall neutral

Question 8

titration: midpoint

Answer 8

PH = pKa

the point at which enough titrant has been added to neutralize half of the analyte

[acid] = [base]

solution is acting as a buffer

Question 9

titration: equivalence point

Answer 9

pH = pI

Question 10

pI

amino acids with neutral R groups

Answer 10

pka1: carboxyl group
pka2: amino group

Question 11

pI

amino acids with basic R groups

Answer 11

pka2: amino group (NH3+)
pka3: R group

Question 12

pI

amino acids with acidic R groups

Answer 12

pka1: carboxyl group (COO-)
pka3: R group

Question 13

amino acids are read from – to – terminus

Answer 13

N to C terminus