1.1 Amino Acids Found in Proteins [HY]

Question 1

All AA’s are optically active/ have a chiral center except?

Answer 1

Glycine, which has a hydrogen atom as its R group, making it achiral

Question 2

All AA’s have a S configuration except?

Answer 2

Cysteine, has an (R) absolute
configuration because the −CH2SH group has priority over the −COOH group

Question 3

What affect does proline’s ring have on it?

Answer 3

That ring places notable constraints on the flexibility of
proline, limiting where it can appear in a protein and can have significant effects on proline’s role in secondary structure.

Question 4

Why are the polar AA’s polar?

Answer 4

B/c of the OH side chains, and therefore able to participate in hydrogen bonding.

Question 5

Why is Sulfur on cysteine more likely to be oxidized?

Answer 5

• sulfur is larger than oxygen, the S−H bond is longer and weaker than the O−H bond
• Oxygen is more electronegative than Sulfur

Question 6

What is physiological pH?

Answer 6

7.4

Question 7

How do most acids exist in cells?

Answer 7

In the deprotonated form

Question 8

Why are positive AA’s positive?

Answer 8

have side chains that have positively charged nitrogen atoms.

Question 9

Which AA’s are hydrophobic?

Answer 9

• A, I, L, V, F
• Most likely in interior of proteins

Question 10

Which AA’s are hydrophilic?

Answer 10

• All positive AA’s (H, R, K)
• Anions of D & E (aspartate, glutamate)
• Amides: N & Q

Question 11

Which AA’s are on the surface of proteins?

Answer 11

• AA’s with charged side chains

Question 12

What is notation for substitution?

Answer 12

• [Letter of initial AA] [AA #] [Letter of final AA]