Q: Which of the following best describes the secondary structure of silk fibroin?

Extensive close-packed $b$-sheet interrupted by compact folded regions

Q: What is the main difference between parallel and antiparallel $b$-sheets?

Parallel $b$-sheets have strands running in the same N to C direction, while antiparallel $b$-sheets have strands running in opposite N to C directions.

Question 1

Which level of protein structure is primarily responsible for the spatial arrangement of multiple polypeptide chains in a multisubunit complex?

Accepted Answer

Quaternary structure

Question 2

In an $b$-sheet, how are the side chains of neighboring amino acids oriented?

Accepted Answer

They alternate on opposite faces of the sheet.

Question 3

Which of the following interactions is NOT a favorable intramolecular enthalpic interaction that stabilizes protein folding?

Accepted Answer

Loss of conformational entropy

Question 4

A mutation replaces a hydrophobic residue in the interior of a globular protein with a charged residue. What is the most likely effect on protein stability?

Accepted Answer

Protein stability will decrease due to disruption of the hydrophobic core.

Question 5

Which protein is characterized by a coiled-coil structure and is a major component of hair and fingernails?

Accepted Answer

Keratin

Question 6

What is the main thermodynamic driving force for the burial of hydrophobic side chains in the interior of a folded protein?

Accepted Answer

Favorable gain of solvent entropy

Question 7

Which of the following best describes the secondary structure of silk fibroin?

Accepted Answer

Extensive close-packed $b$-sheet interrupted by compact folded regions

Question 8

A protein domain is typically about how many amino acids and can fold independently?

Accepted Answer

200 amino acids

Question 9

Which type of bond greatly increases the stability of proteins such as bovine pancreatic trypsin inhibitor?

Accepted Answer

Disulfide bonds

Question 10

Which symmetry is displayed by a tetrameric enzyme with three 2-fold axes?

Accepted Answer

$D_2$ symmetry

Question 11

What is the main difference between parallel and antiparallel $b$-sheets?

Accepted Answer

Parallel $b$-sheets have strands running in the same N to C direction, while antiparallel $b$-sheets have strands running in opposite N to C directions.

Question 12

Which of the following is NOT a fibrous protein?

Accepted Answer

Ubiquitin

Question 13

Which of the following factors can increase the stability of a protein by binding to it?

Accepted Answer

Ions or prosthetic groups

Question 14

Which statement best describes the arrangement of side chains in an $b$-helix?

Accepted Answer

Side chains radiate outward from the helical axis.

Question 15

A protein loses its tertiary structure but retains its secondary structure. Which of the following is most likely to remain intact?

Accepted Answer

The local areas of repeating main chain structure

Question 16

Which of the following is a consequence of the hydrophobic effect during protein folding?

Accepted Answer

Ordered solvent molecules are released from clathrate structures, increasing entropy.

Question 17

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

Accepted Answer

The spatial arrangement of secondary structural elements in the polypeptide chain

Question 18

Which protein structure level is most directly affected by a mutation that changes a single amino acid in the sequence?

Accepted Answer

Primary structure

Question 19

Which of the following is a real-world example of a protein with helical symmetry capable of indefinite growth in length?

Accepted Answer

Actin

Question 20

A protein is found to have twofold symmetry about a $C_2$ axis. Which quaternary structure does it most likely possess?

Accepted Answer

Dimeric $C_2$ symmetry

The Three-Dimensional Structure of Proteins (Chapter 6 Study Notes)

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