BCH CHAPTER 3

For the peptide Ala-Arg-Lys-Ala-Asn-Ser-Ala-Ser, what would be the expected charges at pH 1, 7, and 13?

+3, +2, -1

For aspartic acid at pH = 7, what is the ratio of the concentration of the neutral amino acid species to the negatively charged species (zwitterion backbone and deprotonated side chain)? All pKa values can be found in Table 3.1.

1.6 x 10-9

What percentage of the total set of amino acids can human beings synthesize themselves?

55%

For isoleucine at pH = 2, what is the ratio of the concentration of the zwitterionic amino acid species to the neutral species? All pKa values can be found in Table 3.1.

7.9 x 104

The protonated amino group of an amino acid will lose a proton when the pH approaches:

9

Naturally occurring proteins contain L amino acids. Which of the following is a possible reason for this phenomenon?

A small excess of L amino acids may have existed in the past.

Which of the following lists puts the amino acids in the CORRECT order of ascending numbers of carbon atoms in the side chain?

Ala < Pro < Phe

Which of the following statements about amino acids is TRUE?

Amino acids contain a central α-carbon and are dipolar ions, or zwitterions.

Which amino acid would be positively charged at physiological pH?

Arg

Which of the following statements is TRUE of an amino acid?

At pH 11, the amino group is deprotonated.

Which of the following peptides can an adult human fully synthesize without relying on any essential amino acids?

Gly-Ser-Tyr-Glu-Gln

Of the 20 amino acids from which proteins are made, which is most likely to be present with its R-group in a mixture of ionization states near physiological pH?

His

The one-letter code of amino acids was introduced to facilitate storage of protein sequence information in computers. Which translation of the following sequence into the one-letter code is CORRECT? Met-Ala-Arg-Gly-Glu-Thr-Asn-Tyr-His-Phe-Pro

MARGETNYHFP

The side chain of Q has one more carbon than the side chain of:

N

Which of the following is true regarding the chirality of amino acids found in proteins?

Only L amino acids are found in proteins.

_____ is an aliphatic amino acid, but it differs from others because its side chain is bonded to both the _____ and the _____ of the backbone.

Proline; nitrogen; α-carbon

Which of the following amino acids contains a guanidinium group?

R

For an amino acid with a side chain that is a methyl group, as the pH is raised from 1, which of the following statements is TRUE?

The carboxyl group is the first to lose a proton.

Which of the following characteristics is TRUE for both histidine and lysine?

Their side chains contain four carbon atoms.

Which of the following characteristics is TRUE for both valine and threonine?

They are both neutral at physiological pH (˜pH = 7).

Which of the following lists contain only amino acids with at least one ring structure in the side chain?

Trp; Phe; Tyr

Which of the following is a nonessential amino acid?

alanine

Which of the following is a symptom of kwashiorkor?

both lethargy and irritability

Free amino acids in solution at neutral pH exist predominantly as zwitterions. Another term for this is _____ ions.

dipolar

Four of the 20 amino acids begin with the letter "A." Of these, how many are nonessential amino acids?

four

Which of the following amino acids exists predominantly as a zwitterion? The terminal amino group, terminal carboxyl group, and side chain pKa values can be found in Table 3.1.

glutamic acid at pH = 3.5

Which amino acid has the simplest side chain?

glycine

Which of the following amino acids would contain an overall positive charge at pH 1?

leucine methionine glycine lysine

Essential amino acids must be:

obtained from the diet.

An amino acid contains an R group. Another name for this portion of the amino acid is _____.

side chain

For an amino acid that contains a side chain that is non-ionizable, how many ionizable groups are there on the amino acid?

two