Question 1

Which of the following statements best describes the zwitterionic form of an amino acid at physiological pH?

Accepted Answer

The amino group is protonated and the carboxyl group is deprotonated, resulting in both positive and negative charges but a net zero charge.

Question 2

Which amino acid is unique in that it is not chiral and why?

Accepted Answer

Glycine, because its side chain is a hydrogen atom.

Question 3

A protein sample absorbs strongly at 280 nm. Which amino acids are most likely responsible for this absorbance?

Accepted Answer

Phenylalanine, Tyrosine, and Tryptophan

Question 4

Which of the following amino acids is most likely to form a disulfide bond in an oxidizing environment?

Accepted Answer

Cysteine

Question 5

Given the following pKa values for glycine: $$pK_a$$^{COOH}$$ = 2.4$$, $$pK_a$$^{NH_3^+}$$ = 9.8$$, calculate the isoelectric point ($$pI) of $$glycine.

Accepted Answer

$$pI = \frac{2.4 + 9.8}{2} = 6.1$$

Question 6

Which amino acid is most likely to act as a nucleophile at physiological pH due to its imidazole side chain?

Accepted Answer

Histidine

Question 7

Which property is shared by all biological macromolecules?

Accepted Answer

They are composed of monomeric units and have 3-dimensional, dynamic structures.

Question 8

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

Accepted Answer

Leucine

Question 9

Which modification increases the number of possible side chain functionalities in proteins after translation?

Accepted Answer

Post-translational modification

Question 10

Which of the following amino acids contains a sulfur atom in its side chain and is hydrophobic?

Accepted Answer

Methionine

Question 11

Which amino acid is most likely to participate in hydrogen bonding due to its amide side chain?

Accepted Answer

Asparagine

Question 12

Which of the following is true regarding the stereochemistry of naturally occurring amino acids in proteins?

Accepted Answer

They are all L-enantiomers.

Question 13

Which amino acid is most likely to disrupt alpha-helical structure due to its cyclic side chain?

Accepted Answer

Proline

Question 14

A solution contains an amino acid with a side chain pKa of 4.0. At pH 7, what is the likely charge on the side chain?

Accepted Answer

Negatively charged

Question 15

Which amino acid is most likely to bind reactive metals due to its negatively charged carboxylate side chain at neutral pH?

Accepted Answer

Aspartate

Question 16

Which of the following amino acids is aromatic and can participate in electron resonance?

Accepted Answer

Phenylalanine

Question 17

Which equation describes the Beer-Lambert law used to quantify protein concentration via absorbance?

Accepted Answer

$$A = \epsilon c l$$

Question 18

Which amino acid is most likely to be protonated and positively charged at physiological pH due to its high side chain pKa?

Accepted Answer

Arginine

Question 19

Which of the following best explains why modifications of amino acids are important in proteins?

Accepted Answer

They increase the diversity of protein function and regulation.

Question 20

Which amino acid is most likely to act as a nucleophile only when its side chain is deprotonated at high pH?

Accepted Answer

Lysine

Structure and Properties of Amino Acids

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