Question 1

Which of the following statements best describes the structure of an $$ \alpha -$$amino acid at neutral pH?

Accepted Answer

The amino group is protonated and the carboxylic acid group is deprotonated, resulting in a zwitterion.

Question 2

Which amino acid does NOT have a chiral $$ \alpha -$$carbon?

Accepted Answer

Glycine

Question 3

L-alanine and D-alanine are examples of which type of stereoisomers?

Accepted Answer

Enantiomers

Question 4

Which of the following amino acids is classified as a nonpolar aromatic amino acid?

Accepted Answer

Tryptophan

Question 5

Proteins are commonly quantified by measuring UV absorbance at which wavelength, and which amino acids dominate this absorbance?

Accepted Answer

$$280\ \mathrm{nm}$$; tyrosine and tryptophan

Question 6

What is the typical $$pK_a$$ range for the $$\alpha-$$amino group in amino acids?

Accepted Answer

$$8.0-9.0$$

Question 7

During the titration of histidine, what does the point where the net charge on the molecule is zero represent?

Accepted Answer

The isoelectric point ($$pI)$$

Question 8

Which of the following is a posttranslational modification that can play a role in gene expression or suppression?

Accepted Answer

N-acetyllysine

Question 9

The formation of a peptide bond between two amino acids is best described as:

Accepted Answer

A condensation reaction that releases water

Question 10

Why is peptide bond formation not thermodynamically favorable under physiological conditions?

Accepted Answer

Because it is coupled to ATP hydrolysis to proceed

Question 11

Which property of the peptide bond contributes most to its planarity and stability?

Accepted Answer

Delocalization of electrons across the bond

Question 12

Which of the following statements about peptide bond hydrolysis is correct?

Accepted Answer

Peptide bonds are stable unless exposed to strong acid at high temperature or a catalyst.

Question 13

Trypsin is a protease that cleaves peptide bonds on the carboxyl side of which amino acids?

Accepted Answer

Lysine and arginine

Question 14

A peptide chain consisting of 10 amino acid residues is best classified as:

Accepted Answer

An oligopeptide

Question 15

Which of the following modifications can block the N-terminus of a peptide?

Accepted Answer

N-formyl group

Question 16

As the pH of a solution increases, what happens to the overall charge of a peptide?

Accepted Answer

It becomes more negative

Question 17

Which of the following best explains why proteins are not quantified at 260 nm in UV spectroscopy?

Accepted Answer

Nucleic acids absorb most strongly at 260 nm, while proteins absorb at 280 nm.

Question 18

Which of the following is a correct statement about the ionization behavior of peptides and proteins?

Accepted Answer

As pH increases, the overall charge becomes more negative.

Question 19

A researcher wants to selectively cleave a peptide at methionine residues. Which reagent should they use?

Accepted Answer

Cyanogen bromide

Question 20

Which of the following is a real-life application of posttranslational modification of amino acids?

Accepted Answer

Stabilization of collagen by 4-hydroxyproline

Amino Acids and Peptides: Structure, Properties, and Modifications

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