Question 1

Which of the following statements best describes the isoelectric point ($$pI) of an $$amino acid with a neutral side chain?

Accepted Answer

The $$pI is $$the average of the $$pK_a$$ values for the ammonium and carboxyl groups.

Question 2

A solution contains a mixture of arginine, alanine, and aspartate. At pH 7, which amino acid will migrate toward the cathode during electrophoresis?

Accepted Answer

Arginine

Question 3

Which property of the peptide bond restricts rotation and contributes to protein secondary structure?

Accepted Answer

Resonance stabilization between the carbonyl and amide nitrogen

Question 4

Which of the following amino acids is most likely to be found on the interior of a globular protein?

Accepted Answer

Leucine

Question 5

What is the main chemical reaction that occurs when ninhydrin is used to detect amino acids?

Accepted Answer

Amino acids react with ninhydrin to produce a purple-colored product.

Question 6

Which of the following best explains why hair can be curled or straightened using chemical treatments?

Accepted Answer

Chemical treatments break and reform disulfide bridges in keratin.

Question 7

Which of the following is a covalent interaction that stabilizes the tertiary structure of proteins?

Accepted Answer

Disulfide bridge

Question 8

A protein is denatured by heat. Which level(s) of structure are most likely disrupted?

Accepted Answer

Secondary and tertiary structure

Question 9

Which of the following amino acids would elute last from an ion-exchange chromatography column packed with a negatively charged resin?

Accepted Answer

Lysine

Question 10

Which of the following best describes the $$eta-$$sheet structure in proteins?

Accepted Answer

It is stabilized by hydrogen bonds between NH and CO groups of neighboring segments.

Question 11

Which of the following statements about the quaternary structure of proteins is correct?

Accepted Answer

It involves the assembly of multiple polypeptide subunits.

Question 12

Which amino acid is achiral and why?

Accepted Answer

Glycine, because its side chain is a hydrogen atom.

Question 13

At physiological pH, which of the following amino acids will have a net negative charge?

Accepted Answer

Aspartic acid

Question 14

Which of the following best explains why non-polar amino acids are usually found in the interior of globular proteins?

Accepted Answer

They minimize their exposure to water due to hydrophobic interactions.

Question 15

Which of the following is true about the $$eta-$$sheet and $$eta-$$strand structures?

Accepted Answer

Hydrogen bonds form between NH and CO groups of adjacent strands.

Question 16

A peptide has the sequence Phe-His-Asp-Val. Which end is the N-terminus?

Accepted Answer

Phe

Question 17

Which of the following best describes the effect of pH on the net charge of an amino acid?

Accepted Answer

When pH \u003e pI, the amino acid has a net negative charge.

Question 18

Which of the following is a correct statement about the $$eta-$$sheet and $$eta-$$strand structures?

Accepted Answer

Hydrogen bonds form between NH and CO groups of adjacent strands.

Question 19

Which of the following best explains why the $$pK_a of $$the carboxyl group in amino acids is lower than that of acetic acid?

Accepted Answer

The inductively withdrawing ammonium group stabilizes the carboxylate anion.

Amino Acids, Peptides, and Proteins: Structure, Properties, and Analysis

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