Question 1

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

Accepted Answer

It exists primarily as a zwitterion, with a negatively charged carboxylate group and a positively charged amino group.

Question 2

Which property of the peptide bond is most responsible for its planarity and restricted rotation?

Accepted Answer

Partial double-bond character due to resonance between the carbonyl oxygen and the amide nitrogen.

Question 3

Which amino acid is most likely to be found on the surface of a soluble protein interacting with water?

Accepted Answer

Serine

Question 4

What is the main chemical reaction involved in the formation of a peptide bond between two amino acids?

Accepted Answer

Dehydration synthesis (condensation reaction), releasing a molecule of water.

Question 5

Which amino acid is unique for its cyclic structure, causing rigidity in protein chains and often found at turns?

Accepted Answer

Proline

Question 6

Which of the following amino acids can form covalent disulfide bonds, contributing to protein stability?

Accepted Answer

Cysteine

Question 7

The isoelectric point ($$pI) of an $$amino acid is defined as:

Accepted Answer

The pH at which the amino acid has no net electrical charge.

Question 8

Which of the following best explains why aromatic amino acids such as tryptophan and tyrosine absorb light at 280 nm?

Accepted Answer

Their aromatic rings contain delocalized electrons that interact with UV light.

Question 9

Which of the following amino acids is classified as basic and can participate in salt bridge formation?

Accepted Answer

Lysine

Question 10

Which of the following statements about hydrogen bonds in proteins is correct?

Accepted Answer

Hydrogen bonds are weak but crucial for stabilizing secondary and tertiary protein structures.

Question 11

Which of the following equations correctly represents the formation of a peptide bond between two amino acids?

Accepted Answer

$$\mathrm{Amino\ acid}_1 + \mathrm{Amino\ acid}_2 \rightarrow \mathrm{Dipeptide} + \mathrm{H}_2\mathrm{O}$$

Question 12

Which of the following best describes the role of phi ($$\phi) $$and psi ($$\psi) $$angles in protein structure?

Accepted Answer

They determine the flexibility and folding of the polypeptide backbone.

Question 13

Which of the following amino acids is most likely to be found in the interior of a globular protein?

Accepted Answer

Leucine

Question 14

Which of the following is a correct statement about the stereoisomers of amino acids in proteins?

Accepted Answer

Proteins are composed almost exclusively of L-amino acids.

Question 15

Which of the following amino acids has the greatest hydrogen bonding potential due to its side chain?

Accepted Answer

Glutamine

Question 16

A mutation replaces a hydrophobic amino acid in the core of a protein with a hydrophilic one. What is the most likely effect?

Accepted Answer

The protein may misfold or become less stable due to disruption of hydrophobic interactions.

Question 17

Which of the following best explains the formation of salt bridges in proteins?

Accepted Answer

Ionic interactions between acidic and basic amino acid side chains.

Question 18

Which of the following amino acids is classified as aromatic and has both hydrophobic and polar characteristics?

Accepted Answer

Tyrosine

Question 19

Which of the following bonds is most important for stabilizing the secondary structure of proteins such as alpha helices and beta sheets?

Accepted Answer

Hydrogen bonds between backbone amide and carbonyl groups.

Amino Acids and Fundamentals of Protein Structure: Mini-Textbook Study Notes

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