Question 1

Which of the following statements correctly 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 contain a chiral $$\alpha-$$carbon?

Accepted Answer

Glycine

Question 3

L-alanine and D-alanine are examples of:

Accepted Answer

Enantiomers

Question 4

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

Accepted Answer

Tryptophan

Question 5

At which wavelength do proteins, specifically those containing tyrosine and tryptophan, absorb UV light most strongly?

Accepted Answer

$$280\ \mathrm{nm}$$

Question 6

Which group type has a typical $$pK$$ range of $$8.0-9.0 in $$amino acids?

Accepted Answer

$$\alpha-$$Amino

Question 7

During the titration of histidine, what does the green dot on the titration curve represent?

Accepted Answer

The $$pI$$, where the net charge on the molecule is zero

Question 8

Which posttranslational modification is important for stabilizing collagen structures?

Accepted Answer

4-Hydroxyproline

Question 9

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

Accepted Answer

Thermodynamically unfavorable and is coupled to ATP hydrolysis.

Question 10

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

Accepted Answer

Delocalization of electrons across the bond

Question 11

Peptide bonds are generally stable unless exposed to:

Accepted Answer

Strong acid at high temperature or a catalyst

Question 12

Trypsin is a protease that cleaves peptide bonds at which amino acid residues?

Accepted Answer

Lysine and arginine

Question 13

Which of the following best describes an oligopeptide?

Accepted Answer

A peptide chain with 3–15 residues

Question 14

Which modification can block the N-terminus of a peptide?

Accepted Answer

N-formyl group

Question 15

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

Accepted Answer

It becomes more negative.

Question 16

Which of the following is a real-world application of UV absorbance at 280 nm in biochemistry?

Accepted Answer

Quantifying protein concentration due to aromatic amino acids

Question 17

A peptide contains the following sequence: Glu-Ala-Gly-Lys. At pH 7, what is the expected net charge of the peptide?

Accepted Answer

+1

Question 18

Which of the following statements about the $$pI ($$isoelectric point) of an amino acid is correct?

Accepted Answer

It is the pH at which the net charge of the molecule is zero.

Question 19

Which of the following posttranslational modifications is most likely to play a role in gene expression or suppression?

Accepted Answer

N-acetyllysine

Amino Acids and Peptides: Structure, Properties, and Reactions

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