Question 1

Which of the following statements correctly describes the chirality of protein-derived amino acids?

Accepted Answer

With the exception of glycine, all protein-derived amino acids have at least one stereocenter and are chiral.

Question 2

Which amino acid contains a secondary amino group at its α-carbon?

Accepted Answer

Proline

Question 3

A solution contains a mixture of aromatic amino acids. Which property allows you to estimate their concentration using UV-visible spectrophotometry?

Accepted Answer

Their absorption of light in the UV region, especially around 275-280 nm.

Question 4

Which equation is used to calculate the concentration of an amino acid solution using UV absorbance?

Accepted Answer

$$A = \varepsilon \cdot c \cdot l$$

Question 5

Which amino acid side chain is most likely to form a disulfide bond under oxidizing conditions?

Accepted Answer

Cysteine

Question 6

At pH 7.0, what is the net charge of glycine, given that its α-carboxyl group has $$pK_a = 2.0$$ and its α-amino group has $$pK_a = 10.0$$?

Accepted Answer

0

Question 7

Which amino acid has an indole ring in its side chain?

Accepted Answer

Tryptophan

Question 8

Which of the following amino acids contains a thiol (-SH) group in its side chain?

Accepted Answer

Cysteine

Question 9

What is the isoelectric point ($$pI) of $$glycine if its $$pK_a$$ values are $$2.35 ($$carboxyl) and $$9.78 ($$amino)?

Accepted Answer

$$pI = \frac{2.35 + 9.78}{2} = 6.065$$

Question 10

Which amino acid is most likely to be positively charged at physiological pH (7.0)?

Accepted Answer

Arginine

Question 11

Which of the following best describes a peptide bond?

Accepted Answer

A covalent bond between the α-carboxyl group of one amino acid and the α-amino group of another.

Question 12

Which amino acid has a side chain that is aromatic and can absorb UV light strongly?

Accepted Answer

Tryptophan

Question 13

Which amino acid contains a guanidino group in its side chain, making it a strong base?

Accepted Answer

Arginine

Question 14

Which of the following amino acids has a side chain with an amide bond?

Accepted Answer

Asparagine

Question 15

If the pH of a solution is below the $$pK_a of an $$amino acid's carboxyl group, what is the predominant form of the carboxyl group?

Accepted Answer

Protonated ($$-COOH)$$

Question 16

Which amino acid is unique in that it does not have a chiral α-carbon?

Accepted Answer

Glycine

Question 17

Which of the following amino acids has a side chain that is both aromatic and contains a hydroxyl group?

Accepted Answer

Tyrosine

Question 18

Which amino acid is most likely to be found in the interior of a protein due to its nonpolar side chain?

Accepted Answer

Leucine

Question 19

Which of the following is the correct one-letter abbreviation for threonine?

Accepted Answer

T

Question 20

A peptide is synthesized with the sequence Gly-Cys-Tyr. If oxidizing conditions are applied, which structural change is most likely to occur?

Accepted Answer

Formation of a disulfide bond between two Cys residues.

Amino Acids: Structure, Classification, and Properties

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