Question 1

Which of the following best describes the main stabilizing force in an α-helix secondary structure of proteins?

Accepted Answer

Hydrogen bonds between the backbone C=O of residue $$i$$ and the N–H of residue $$i+4$$

Question 2

A Ramachandran plot is used to visualize which of the following properties of protein structure?

Accepted Answer

The allowed combinations of backbone dihedral angles $$\phi ($$phi) and $$\psi ($$psi)

Question 3

Which amino acid is most likely to disrupt an α-helix due to its rigid, cyclic structure?

Accepted Answer

Proline

Question 4

Which of the following statements about β-sheets is TRUE?

Accepted Answer

Hydrogen bonds form between backbone atoms of adjacent β-strands

Question 5

Which of the following best explains why L-amino acids favor right-handed α-helices in proteins?

Accepted Answer

The geometry of L-amino acids avoids steric clashes and allows optimal backbone hydrogen bonding in right-handed helices

Question 6

A protein region contains several lysine (Lys) and glutamate (Glu) residues at positions $$i$$ and $$i+4 in an$$ α-helix. What is the most likely effect on helix stability?

Accepted Answer

Stabilization due to formation of a salt bridge (ionic interaction)

Question 7

Which of the following is a key difference between fibrous and globular proteins?

Accepted Answer

Fibrous proteins have simple, repetitive secondary structures and are insoluble in water, while globular proteins are compact and soluble

Question 8

Which of the following amino acid sequences is most likely to be found in the hydrophobic core of a membrane-spanning α-helix?

Accepted Answer

Leu–Ile–Val–Phe

Question 9

Which of the following best describes the quaternary structure of a protein?

Accepted Answer

The arrangement of multiple polypeptide subunits in a protein complex

Question 10

A mutation replaces a glycine residue with a bulky tryptophan in the center of a collagen triple helix. What is the most likely consequence?

Accepted Answer

The triple helix will be destabilized due to steric clashes

Question 11

Which of the following best explains why intrinsically disordered proteins can interact with multiple binding partners?

Accepted Answer

They lack a stable hydrophobic core and are enriched in flexible, charged residues

Question 12

Which of the following is TRUE regarding the formation of β-turns in proteins?

Accepted Answer

Glycine is often found at position 3 of a type II β-turn due to its small size

Question 13

Which of the following best describes the main difference between parallel and antiparallel β-sheets?

Accepted Answer

Antiparallel β-sheets have hydrogen bonds that are more linear and thus stronger than those in parallel β-sheets

Question 14

Which of the following is a correct statement about the peptide bond in proteins?

Accepted Answer

It has partial double-bond character, restricting rotation around the C–N bond

Question 15

Which of the following best explains why hydrophobic residues are often found buried inside globular proteins?

Accepted Answer

The hydrophobic effect drives nonpolar side chains to the protein interior, away from water

Question 16

Which of the following motifs is commonly found in protein tertiary structures and consists of a β-strand, an α-helix, and another β-strand connected by loops?

Accepted Answer

β-α-β loop

Question 17

Which of the following best describes a protein superfamily?

Accepted Answer

A group of proteins with similar structural motifs and probable evolutionary relationships, but little sequence similarity

Question 18

Which of the following is a plausible consequence of a mutation that introduces several charged residues on one face of an amphipathic α-helix?

Accepted Answer

The helix may become destabilized due to charge repulsion if the charges are the same

Question 19

Which of the following best describes the hierarchical organization of protein structure?

Accepted Answer

Primary → Secondary → Tertiary → Quaternary

Protein Structure and Folding: Secondary, Tertiary, and Quaternary Organization

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