Q: Which of the following statements about $$b-$$sheets is correct?

$$b-$$sheets are stabilized by interchain hydrogen bonds and have side chains that alternate above and below the plane of the sheet

Q: Keratin is a fibrous protein found in hair and nails. Which structural feature is most characteristic of keratin?

A coiled-coil structure formed by two $$b-$$helices with hydrophobic side chains at the interface

Question 1

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 2

A mutation causes a hydrophobic amino acid in the core of a globular protein to be replaced by a hydrophilic one. Which of the following is the most likely consequence?

Accepted Answer

The protein's stability will decrease due to disruption of the hydrophobic effect

Question 3

Which of the following statements about $$b-$$sheets is correct?

Accepted Answer

$$b-$$sheets are stabilized by interchain hydrogen bonds and have side chains that alternate above and below the plane of the sheet

Question 4

Keratin is a fibrous protein found in hair and nails. Which structural feature is most characteristic of keratin?

Accepted Answer

A coiled-coil structure formed by two $$b-$$helices with hydrophobic side chains at the interface

Question 5

Which of the following interactions is NOT a major contributor to the stabilization of protein tertiary structure?

Accepted Answer

Peptide bond resonance

Question 6

A protein is found to have a quaternary structure with $$D_2$$ symmetry. Which of the following best describes this symmetry?

Accepted Answer

The protein has three 2-fold axes of symmetry

Question 7

Which of the following best explains the 'hydrophobic effect' in protein folding?

Accepted Answer

Burying hydrophobic side chains in the protein interior releases ordered water molecules, increasing solvent entropy

Question 8

Which of the following is a correct statement about the $$b-$$helix secondary structure?

Accepted Answer

Side chains radiate outward from the helix axis, and hydrogen bonds are nearly parallel to the helix axis

Question 9

Which of the following is a real-world example of a protein with a triple helix structure, and what is its biological role?

Accepted Answer

Collagen, which provides structural support in connective tissues and bone

Question 10

A researcher is studying a protein that contains two distinct domains, each capable of folding independently. Which level of protein structure does this observation most directly relate to?

Accepted Answer

Tertiary structure

Question 11

Which of the following best describes the entropy changes during protein folding?

Accepted Answer

The conformational entropy of the protein decreases, but the entropy of the solvent increases due to the hydrophobic effect

Question 12

Disulfide bonds are important for protein stability. Which amino acid is directly involved in forming disulfide bonds?

Accepted Answer

Cysteine

Question 13

A protein is found to be composed of four identical subunits arranged with $$C_2$$ symmetry. Which of the following is true about its quaternary structure?

Accepted Answer

It has a 2-fold axis of symmetry

Question 14

Which of the following statements about protein domains is correct?

Accepted Answer

A domain is a compact, independently folding region of a protein, often associated with a specific function

Question 15

Which of the following is a key difference between parallel and antiparallel $$b-$$sheets?

Accepted Answer

In parallel $$b-$$sheets, the strands run in the same direction (N $$ 3e C$$), while in antiparallel $$b-$$sheets, one strand runs N $$ 3e C $$and the other C $$ 3e N$$

Question 16

Which of the following is a major reason why proteins are densely packed in their native folded state?

Accepted Answer

Van der Waals interactions maximize favorable contacts between atoms

Question 17

A patient has a genetic disorder that prevents the formation of disulfide bonds in certain proteins. Which of the following is a likely consequence?

Accepted Answer

The affected proteins will be less stable and more susceptible to denaturation

Question 18

Which of the following best explains why binding of ions or prosthetic groups can increase protein stability?

Accepted Answer

They provide additional stabilizing interactions that help maintain the protein's folded structure

Question 19

Which of the following is a correct statement about the structure of fibroin in silk?

Accepted Answer

Fibroin consists of extensive close-packed $$b-$$sheets interrupted by compact folded regions that provide elasticity

The Three-Dimensional Structure of Proteins: Levels, Elements, and Stability

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