Amino Acids

Question 1

Which AA are acidic? What makes them acidic? Inc. 1 letter and 3 letter abbreviations

Answer 1

D-Aspartic Acid, Asp
E-Glutamic Acid, Glu
The R group contains a COOH

Question 2

What AA are basic? What makes them basic? Inc. 1 letter and 3 letter abbreviations

Answer 2

K-Lysine, lys
R-Arginine, arg
H-Histamine, his
The R group contains an amine group: NH2 for lys and arg, NH for his

Question 3

What is the pKa of an acidic AA? What are the aproximate pKas of the basic AA?

Answer 3

acidic AA pKa ~4
basic AA: 
-lysine ~10
-arginine ~12
-histidine ~6.5

Question 4

Out of the acidic and basic AA, which are protonated and which are deprotonated at phsyiological pH?

Answer 4

Aspartic Acid, Glutamic Acid, and Histidine tend to be protonated at physiological pH
Lysine and Arginine tend to be deprotonated at physiological pH

Question 5

Which AA are nonpolar? Inc. 1 letter and 3 letter abbreviations

Answer 5

F-phenylalanine
L-Leucine
A-Alanine
W-Tryptophan
V-Valine
I-Isoleucine
G-Glycine

Question 6

What is the simplest AA? Why?

Answer 6

Glycine because its R group is only H

Question 7

What nonpolar AA have ring structures on their R group?

Answer 7

Phenylalanine and Tryptophan

Question 8

Where are nonpolar AA residues typically found within a protein and why?

Answer 8

Found on the interior of a folded globular protein so that it doesn’t interact with water.

Question 9

What are the polar AA? Inc. 1 letter and 3 letter abbreviations

Answer 9

S-Serine, ser 
T-Threonine, thr 
Y-Tyrosine, tyr 
N-Asparagine, asn
Q-Glutamine, gln

Question 10

What group makes the polar AA polar?

Answer 10

For serine, threonine, and tyrosine, an OH on the R group creates polarity
For asparagine and glutamine, the NH2 on the R group creates polarity

Question 11

For the polar AA, the hydroxyl groups of serine, threonine, and tyrosine residues are often modified by the attachment of a __1__ group by a regulatory enzyme called a __2__

Answer 11

1. phosphate

2. kinase

Question 12

What does quality does the added phosphate group have when added to serine, threonine, or tyrosine?

Answer 12

it adds more hydrophilicity to the AA

Question 13

What are the 2 sulfur containing AA and which one produces disulfide bridges? Inc. 1 letter and 3 letter abbreviations

Answer 13

C-cysteine, cys (contains a thiol, SH)

M-methionine, met (contains a thioether)

Question 14

Out of the 2 sulfur containing AA, which one is fairly polar and which fairly nonpolar?

Answer 14

cysteine is fairly polar d/t SH (like an alcohol but S instead of O)
methionine is fairly nonpolar d/t thioether (like an ether but S instead of O)

Question 15

Why is proline a unique AA?

Answer 15

it’s R group is bonded to its nonpolar side chain (amine group), creating a secondary alpha-amino group and a distinctive ring structure

Question 16

What are the nine essential AA?

Answer 16

Lysine (K), Histidine (H), Threonine (T), Valine (V), Leucine (L), Isoleucine (I), Phenylalanine (F), Tryptophan (W), Methionine (M)

Mneumonic = FVK WHILMY

Question 17

AA are amphoteric, which means AA can act as ____ or ____

Answer 17

acids or bases

Question 18

What’s the approx. pKa of the carboxyl groups?

Answer 18

2

Question 19

What’s the approx. pKa of the ammonium groups?

Answer 19

9 or 10

Question 20

When the pH of a solution is less than the pKa of an acidic group, the acidic group will mostly be in its _____ form.

Answer 20

protonated

Question 21

When the pH of a solution is more than the pKa of an acidic group, the acidic group will be in its ____ form.

Answer 21

deprotonated

Question 22

Which functional groups have a stronger tendency to donate protons, carboxyl groups or ammonium groups?

Answer 22

carboxyl groups

Question 23

All AA have an amino group that acts as a(n) __1__ and a carboxyl that acts as a(n) __2___

Answer 23

1. base

2. acid