Question 1

Which of the following statements correctly describes the structure of an α-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 α-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

Phenylalanine

Question 5

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

Accepted Answer

280 nm; tyrosine and tryptophan

Question 6

Given the following $$pK_a$$ values for the ionizable groups in histidine: $$pK_1 = 1.8$, pK_2$ = 6.0$$, and $$pK_3 = 9.2$, calculate the isoelectric point (pI$) for histidine.

Accepted Answer

$$pI = \frac{6.0 + 9.2}{2} = 7.6$$

Question 7

Which posttranslational modification is most likely to play a role in stabilizing collagen structure?

Accepted Answer

4-Hydroxyproline

Question 8

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

Accepted Answer

A condensation reaction that releases water

Question 9

Why is peptide bond formation not thermodynamically favorable, and how is it achieved in cells?

Accepted Answer

It is not favorable because it requires energy input, and is achieved by coupling to ATP hydrolysis.

Question 10

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

Accepted Answer

Delocalization of electrons between the carbonyl oxygen and amide nitrogen

Question 11

Peptide bonds are generally stable under physiological conditions. Which of the following will efficiently cleave peptide bonds?

Accepted Answer

Strong acid at high temperature or a protease catalyst

Question 12

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

Accepted Answer

Lysine and arginine

Question 13

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

Accepted Answer

An oligopeptide

Question 14

Which modification can block the N-terminus of a peptide, preventing further extension or degradation?

Accepted Answer

N-formyl group

Question 15

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

Accepted Answer

It becomes more negative.

Question 16

Which of the following $$pK_a$$ ranges is typical for the α-amino group of amino acids?

Accepted Answer

$$8.0 - 9.0$$

Question 17

A patient is found to have a mutation that prevents the posttranslational modification of glutamate to γ-carboxyglutamate. Which physiological process is most likely to be affected?

Accepted Answer

Calcium binding in blood clotting

Question 18

Which of the following best describes a polyampholyte?

Accepted Answer

A molecule containing both acidic and basic groups that can act as both an acid and a base

Question 19

Which amino acid side chain has a $$pK_a$$ value typically in the range $$6.5 - 7.4$$?

Accepted Answer

Imidazole (histidine)

Question 20

A researcher wants to block the C-terminus of a peptide to prevent carboxypeptidase digestion. Which modification should be used?

Accepted Answer

C-terminal amide

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