Chapter 1 Concept Checks

Question 1

What are the four groups attached to the central (α) carbon of proteinogenic amino acid?

Answer 1

The four groups are an amino group (-NH2), a carboxylic acid group (-Cooh), a hydrogen atom, and a R group.

Question 2

What is the stereochemistry of the chiral amino acids that appear in the eukaryotic proteins? (R) or (S)? (Exception)

Answer 2

All chiral amino acids are (S) configuration, with the exception of cysteine (because cycteine is the only amino acid with an R group that has a higher priority than a carboxylic acid).

Question 3

What is the stereochemistry of the chiral amino acids that appear in eukaryotic proteins? L or D?

Answer 3

All chiral eukaryotic amino acid are L

Question 4

Which amino acids fit into each of these categories?

Nonpolar, nonaromatic (7)

Answer 4

Glycine, Analine, Valine, Leucine, Isoleucine, Methionine, Proline

Question 5

Which amino acids fit into each of these categories?

Aromatic (3)

Answer 5

Tryptophan, Phenylanaline, Tyrosine

Question 6

Which amino acids fit into each of these categories?

Polar (5)

Answer 6

Serine, Threonine, Asparagine, Glutamine, Cysteine

Question 7

Which amino acids fit into each of these categories?

Negatively charged/acidic (2)

Answer 7

Aspartate, Glutamate

Question 8

Which amino acids fit into each of these categories?

Positively charged/basic (3)

Answer 8

Lysine, Arginine, Histidine

Question 9

Where do hydrophobic amino acids tend to reside within a protein?

Answer 9

Hydrophobic amino acids tend to reside in the interior of a protein, away from water.

Question 10

Where do hydrophilic amino acids tend to reside within a protein?

Answer 10

Hyrdophilic amino acids tend to remain on the surface of the protein, in contact with water.

Question 11

Identify the amino acid by its one letter abbreviation.

Answer 11

From left to right the amino acids are methionine (M), cysteine (C), alanine (A), and threonine (T).

Question 12

For a generic amino acids, NH2CRHCOOC, with an uncharged side chain, what would be the predominant form at each of the following pH values?
pH = 1
pH = 7
pH =11

Question 13

Given the following pKa values, what is the the value of the pI the amino acid?
Aspartic Acid:
pKa1 = 1.88
pKa2 = 3.65
pKa3 = 9.60

Answer 13

pI = 2.77

(1.88 + 3.65) divided by 2

Question 14

Given the following pKa values, what is the the value of the pI the amino acid?
Arginine:
pKa1 = 2.17
pKa2 = 9.04
pKa3 = 12.48

Answer 14

pI = 10.76

(9.04 + 12.48) divided by 2

Question 15

Given the following pKa values, what is the the value of the pI the amino acid?
Valine:
pKa1 = 2.32
pKa2 = 9.62

Answer 15

pI = 5.97

(2.32 + 9.62) divided by 2

Question 16

1.3 is next