Question 1

Which of the following statements correctly describes the structure of an α-amino acid at neutral pH?

Accepted Answer

The α-amino group is protonated and the carboxylic acid group is deprotonated, forming 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 amino acid side chain absorbs UV light most strongly at 280 nm?

Accepted Answer

Tryptophan

Question 5

What is the typical $$pK_a$$ range for the carboxyl group in amino acids?

Accepted Answer

$$3.5-4.0$$

Question 6

During the titration of histidine, what does the $$pI ($$isoelectric point) represent?

Accepted Answer

The pH at which the net charge on histidine is zero.

Question 7

Which of the following is a posttranslational modification that can stabilize collagen?

Accepted Answer

4-Hydroxyproline formation

Question 8

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

Accepted Answer

A condensation reaction that releases water and is coupled to ATP hydrolysis.

Question 9

Why is the peptide bond planar and stable?

Accepted Answer

Due to delocalization of electrons between the carbonyl and amide nitrogen.

Question 10

Which condition is required to hydrolyze peptide bonds in proteins in vitro?

Accepted Answer

Strong acid at high temperature or a catalyst

Question 11

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

Accepted Answer

After lysine and arginine

Question 12

Which of the following best describes an oligopeptide?

Accepted Answer

A peptide chain with 3–15 residues

Question 13

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

Accepted Answer

N-formyl group

Question 14

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

Accepted Answer

It becomes more negative.

Question 15

Which amino acid is most likely to participate in calcium binding due to posttranslational modification?

Accepted Answer

γ-Carboxyglutamate

Question 16

A protein sample is quantified by measuring its absorbance at 280 nm. Which amino acids contribute most to this absorbance?

Accepted Answer

Tyrosine and tryptophan

Question 17

Which of the following is TRUE about the ionization behavior of peptides and proteins?

Accepted Answer

At high pH, peptides have a net negative charge.

Question 18

Which of the following groups has a $$pK_a$$ value closest to 10 in amino acids?

Accepted Answer

Side-chain amino group (lysine)

Question 19

Which of the following statements about peptide bond formation is CORRECT?

Accepted Answer

It is coupled to ATP hydrolysis during protein biosynthesis.

Question 20

Which of the following is a function of posttranslational modifications of amino acids?

Accepted Answer

Stabilizing protein structures such as collagen

Amino Acids and Peptides: Structure, Properties, and Classification

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