Question 1

Which of the following statements best describes the structure of an amino acid at physiological pH (pH = 7)?

Accepted Answer

The amino group is protonated ($$\mathrm{NH_3$^+}) $$and the carboxyl group is deprotonated ($$\mathrm{COO^-}$$), forming a zwitterion.

Question 2

Which amino acid is the only achiral amino acid found in proteins?

Accepted Answer

Glycine

Question 3

A peptide bond is formed by a condensation reaction between which two functional groups?

Accepted Answer

An amino group and a carboxyl group

Question 4

Which of the following amino acids contains a thiol group in its side chain?

Accepted Answer

Cysteine

Question 5

What is the isoelectric point ($$pI) of $$glycine given $$pK_1 = 2.34$ and pK_2$ = 9.60$$?

Accepted Answer

$$pI = \dfrac{2.34 + 9.60}{2} = 5.97$$

Question 6

Which of the following best explains why most amino acids found in proteins are L-amino acids?

Accepted Answer

The ribosome specifically recognizes and incorporates only L-amino acids during protein synthesis.

Question 7

Which of the following amino acids is classified as aromatic and amphipathic due to its side chain?

Accepted Answer

Tyrosine

Question 8

A mutation replaces a serine residue with an aspartate in a protein. Which of the following changes is most likely to occur?

Accepted Answer

The residue changes from polar, uncharged to negatively charged at pH 7.

Question 9

Which enzyme catalyzes the removal of a phosphate group from a phosphorylated amino acid residue?

Accepted Answer

Phosphatase

Question 10

Which of the following statements about peptide directionality is correct?

Accepted Answer

Peptide sequences are written from the N-terminal to the C-terminal.

Question 11

Which of the following amino acids would have the highest isoelectric point ($$pI$$)?

Accepted Answer

Lysine

Question 12

Which property allows aromatic amino acids to be used in the determination of protein concentration by UV spectroscopy?

Accepted Answer

They absorb UV light at around 280 nm.

Question 13

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

Accepted Answer

At pH equal to the pI, the amino acid has a net zero charge.

Question 14

Which of the following is a real-world application of the green fluorescent protein (GFP) as shown in the study materials?

Accepted Answer

GFP is used as a marker to visualize gene expression in living organisms.

Question 15

Which of the following amino acids is most likely to be found in the peptidoglycan of bacterial cell walls as a D-isomer?

Accepted Answer

D-Alanine

Question 16

A peptide has the sequence Ser-Gly-Tyr-Ala-Leu. How many peptide bonds are present in this peptide?

Accepted Answer

4

Question 17

Which of the following best describes the role of kinases in protein modification?

Accepted Answer

Kinases add phosphate groups to proteins using ATP as a donor.

Question 18

Which of the following amino acids is most likely to act as a buffer at physiological pH due to its side chain pKa being close to 7?

Accepted Answer

Histidine

Question 19

Which of the following statements about peptide bonds is correct?

Accepted Answer

Peptide bonds are planar and have partial double-bond character.

Amino Acids and Peptides: Structure, Properties, and Reactions

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