Chapter 3: Amino Acids

Question 1

Glycine

Gly

G

Question 2

Alanine

Ala

A

Question 3

Proline

Pro

P

Question 4

Valine

Val

V

Question 5

Leucine

Leu

L

Question 6

Isoleucine

Ile

I

Question 7

Methionine

Met

M

Question 8

Phenylalanine

Phe

F

Question 9

Tyrosine

Tyr

Y

Question 10

Tryptophan

Trp

W

Question 11

Serine

Ser

S

Question 12

Threonine

Thr

T

Question 13

Cysteine

Cys

C

Question 14

Asparagine

Asn

N

Question 15

Glutamine

Gln

Q

Question 16

Lysine

Lys

K

Question 17

Arginine

Arg

R

Question 18

Histidine

His

H

Question 19

Aspartate

Asp

D

Question 20

Glutamate

Glu

E

Answer 21

Glycine

Gly

G

Answer 22

Alanine

Ala

A

Answer 23

Proline

Pro

P

Answer 24

Valine

Val

V

Answer 25

Leucine

Leu

L

Answer 26

Isoleucine

Ile

I

Answer 27

Methionine

Met

M

Answer 28

Phenylalanine

Phe

F

Answer 29

Tyrosine

Tyr

Y

Answer 30

Tryptophan

Trp

W

Answer 31

Serine

Ser

S

Answer 32

Threonine

Thr

T

Answer 33

Cysteine

Cys

C

Answer 34

Asparagine

Asn

N

Answer 35

Glutamine

Gln

Q

Answer 36

Lysine

Lys

K

Answer 37

Arginine

Arg

R

Answer 38

Histidine

His

H

Answer 39

Aspartate

Asp

D

Answer 40

Glutamate

Glu

E

Question 41

The amino acid residues in protein molecules are almost exclusively which stereoisomer?

Answer 41

L-stereoisomers.

Question 42

Which are nonpolar aliphatic and why?

Answer 42

Gly: R group is just a Hydrogen. No polarity, Hydrophobic.

Ala: R group is a CH3 which is nonpolar and hydrophobic

Proline: R group made up of C’s and H’s that connect back to the amino group. It is NP and hydrophobic.

Valine: R group C’s and H’s

Leucine

Isoleucine

Methionine: R group has an S but is nonpolar

Question 43

Which are aromatic?

Answer 43

F, Y, W

Question 44

Which are polar and uncharged?

Answer 44

S, T, C, N, Q

Question 45

Which are positively charged?

Answer 45

K, R, H

Question 46

Which are negatively charged?

Answer 46

D, E

Question 47

What is a zwiterion?

Answer 47

German for “hybrid Ion”, which can act as either an acid or a base. Amphoteric: can act as a base or acid. Ampholytes: amphoteric electrolytes

Question 48

What are the normal pKa’s of acetic acid and methylamine? How do the carboxyl and amino groups in an amino acid affect this?

Answer 48

4.8 and 10.6

Repulsion from the positively charged amino group and the departing proton lowers the pKa for the carboxyl group. The opposite charges for the NH3+ and COO- groups stablize the zwitterion, thereby lowering the pKa.

Alpha amino acid (glycine) = 2.34 and 9.60

Question 49

What is an isoelectric point or Isoelectric pH?

Answer 49

pI: The characteristic pH at which the net electric charge is zero. This is useful in protein purification.

Question 50

What is the difference between oligopeptides, polypeptides, and proteins?

Answer 50

Oligopeptides only have a few amino acid residues, polypeptides and proteins have many residues. Polypeptides generally have a molecular weight under 10,000. Proteins are higher.