Question 1

Which of the following best describes the general structure of an alpha-amino acid used in proteins?

Accepted Answer

A central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group.

Question 2

At physiological pH (approximately 7), what is the predominant form of an alpha-amino acid?

Accepted Answer

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

Question 3

Which amino acid side chain can form a disulfide bond, contributing to protein stability?

Accepted Answer

Cysteine

Question 4

Which of the following amino acids is most likely to be found buried within the hydrophobic core of a protein?

Accepted Answer

Valine

Question 5

A mutation replaces a glutamic acid residue with a valine in a protein. Which of the following is a likely consequence?

Accepted Answer

The protein may lose its function due to disruption of ionic interactions and altered folding.

Question 6

Which pair of amino acids can form a stabilizing ionic bond in a protein structure?

Accepted Answer

Glutamate and Arginine

Question 7

What is the significance of the pKa value of an amino acid side chain in the context of protein function?

Accepted Answer

It determines whether the side chain is charged or uncharged at physiological pH, affecting protein structure and interactions.

Question 8

Which of the following statements about chirality in amino acids is correct?

Accepted Answer

All proteinogenic amino acids (except glycine) are chiral and only the L-isomer is used in proteins.

Question 9

Which rule is used to assign the D- or L- configuration to amino acids?

Accepted Answer

The CORN rule

Question 10

Which of the following best describes a peptide bond?

Accepted Answer

A covalent bond formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another.

Question 11

Which amino acid is most likely to participate in acid-base catalysis due to its side chain pKa being close to physiological pH?

Accepted Answer

Histidine

Question 12

A protein's function is lost when a single amino acid is mutated. Which property of proteins does this illustrate?

Accepted Answer

The precise sequence of amino acids determines the protein's 3D structure and function.

Question 13

Which of the following amino acids is uncharged at neutral pH and can form hydrogen bonds through its side chain?

Accepted Answer

Serine

Question 14

Which of the following is a correct statement about the pKa of the alpha-amino group in amino acids?

Accepted Answer

It typically ranges from 8.8 to 9.7.

Question 15

Which amino acid is most likely to be involved in forming a salt bridge with glutamic acid in a protein structure?

Accepted Answer

Arginine

Question 16

Which of the following best explains why proteins must adopt the correct 3D shape?

Accepted Answer

The correct shape is essential for the protein to perform its specific cellular function.

Question 17

Which of the following amino acids contains a sulfur atom in its side chain and is uncharged at neutral pH?

Accepted Answer

Cysteine

Question 18

Which of the following is a real-world example of the importance of amino acid sequence in medicine?

Accepted Answer

Vemurafenib only kills cancer cells with a specific amino acid mutation in BRAF.

Question 19

Which of the following statements about the Cahn-Ingold-Prelog (CIP) rules is correct?

Accepted Answer

They are used to assign R or S configuration to chiral centers, including amino acids.

Question 20

Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both a positive and a negative charge, but overall electrically neutral.

Amino Acids, Peptides, and Proteins: Structure, Properties, and Biological Relevance

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