Question 1

Which structural change in a protein is most directly associated with the formation of amyloid fibrils, as shown in the first image?

Accepted Answer

Local unfolding of destabilized regions leading to association of unfolded regions

Question 2

In the context of protein structure, what is the main role of the heme group shown in the second image?

Accepted Answer

It acts as a prosthetic group enabling oxygen binding and transport

Question 3

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

Accepted Answer

The association of multiple polypeptide chains into a functional complex

Question 4

A patient is diagnosed with amyloidosis, as shown in the whole-body scan. Which molecular event is most likely responsible for the dark areas observed in the scan?

Accepted Answer

Accumulation of misfolded proteins forming insoluble fibrils

Question 5

Which of the following statements about the phi ($\phi$) and psi ($\psi$) angles in a polypeptide backbone is correct?

Accepted Answer

$\phi$ is the angle around the N–C$_\alpha$ bond, and $\psi$ is the angle around the C$_\alpha$–C bond

Question 6

Which secondary structure is characterized by a tighter spiral and is less common in proteins compared to the alpha helix?

Accepted Answer

3$_{10}$ helix

Question 7

What is the main difference between parallel and antiparallel beta sheets?

Accepted Answer

Antiparallel beta sheets have adjacent strands running in opposite directions, while parallel beta sheets have strands running in the same direction

Question 8

Which of the following Ramachandran plot regions is most likely to be sterically forbidden due to atomic crowding?

Accepted Answer

$\phi = 0^\circ$, \psi = 0^\circ$

Question 9

A mutation causes a destabilization of the helical regions in a globin protein. What is the most likely consequence at the molecular level?

Accepted Answer

Increased formation of amyloid fibrils due to exposure of hydrophobic regions

Question 10

Which equation best represents the rise per residue ($d$) in an antiparallel beta strand, given a pitch ($p$) of 6.8 Å and 2 residues per turn?

Accepted Answer

$d = \frac{p}{2}$

Question 11

Which of the following is a real-world consequence of protein misfolding and aggregation?

Accepted Answer

Formation of amyloid plaques in Alzheimer's disease

Question 12

Which feature distinguishes the tertiary structure of a protein from its secondary structure?

Accepted Answer

Tertiary structure involves the overall three-dimensional folding, including interactions between side chains

Question 13

Which of the following best explains why certain phi ($\phi$) and psi ($\psi$) angle combinations are not allowed in polypeptide chains?

Accepted Answer

They result in steric clashes between main-chain atoms

Question 14

Which of the following is true regarding the handedness of polypeptide helices?

Accepted Answer

Right-handed alpha helices are more common in proteins than left-handed helices

Question 15

A protein's secondary structure is disrupted by a mutation. Which of the following is the most likely immediate effect?

Accepted Answer

Loss of regular alpha helices and beta sheets, leading to local unfolding

Question 16

Which of the following best describes the role of side chains in protein structure?

Accepted Answer

They participate in tertiary structure by forming interactions such as hydrogen bonds, ionic bonds, and hydrophobic interactions

Question 17

Which of the following is a characteristic feature of an antiparallel beta sheet?

Accepted Answer

Strands run in opposite directions and hydrogen bonds are nearly perpendicular to the strands

Question 18

Which of the following is most likely to occur if a protein's tertiary structure is disrupted but its secondary structure remains intact?

Accepted Answer

The protein may lose its biological function due to improper folding

Question 19

Which of the following is the correct definition of the pitch ($p$) of a helix in protein secondary structure?

Accepted Answer

$p$ is the distance along the helix axis for one complete turn of the helix

Chapter 6.1

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