$$n \cdot \lambda = 2d \sin \theta$$

Question 1

Which of the following best explains why nonpolar amino acid residues are typically found in the interior of a globular protein?

Accepted Answer

Nonpolar residues are attracted to the hydrophobic core due to the hydrophobic effect, minimizing their exposure to water.

Question 2

A biochemist is attempting to determine the structure of a 150 kDa membrane protein. Which technique is most likely to be successful and why?

Accepted Answer

Cryo-electron microscopy, because it does not require crystallization and is suitable for large complexes.

Question 3

Which of the following is a major disadvantage of X-ray crystallography for protein structure determination?

Accepted Answer

It requires the protein to be crystallized, which is often difficult.

Question 4

The phase problem in X-ray crystallography refers to:

Accepted Answer

The loss of information about the phase of diffracted waves, which is necessary to reconstruct the electron density map.

Question 5

Which of the following statements about protein folding is correct?

Accepted Answer

Proteins fold in directed pathways, often with the help of chaperones, to reach their native conformation efficiently.

Question 6

A protein is denatured by urea and then renatured by removing the urea and oxidizing the protein. What does this experiment demonstrate?

Accepted Answer

The primary amino acid sequence contains all the information necessary for the protein to fold into its native structure.

Question 7

Which of the following best describes the role of molecular chaperones in protein folding?

Accepted Answer

They bind to unfolded or misfolded proteins to prevent aggregation and assist in proper folding.

Question 8

Which of the following is a key feature of prion diseases such as Creutzfeldt-Jakob disease?

Accepted Answer

They result from the misfolding of a normal protein into a pathogenic conformation that can induce misfolding in other proteins.

Question 9

Which of the following equations represents Bragg's Law, which is fundamental to X-ray crystallography?

Accepted Answer

$$n \cdot \lambda = 2d \sin 	heta$$

Question 10

A hydropathy plot is used to:

Accepted Answer

Estimate which regions of a protein are likely to be hydrophobic or hydrophilic.

Question 11

Which of the following statements about NMR spectroscopy in protein structure determination is correct?

Accepted Answer

NMR provides information about proteins in solution and can reveal dynamic aspects of structure.

Question 12

Which of the following is a common feature of protein quaternary structure?

Accepted Answer

Subunits are arranged with only rotational symmetry, such as cyclic or dihedral symmetry.

Question 13

Which of the following best explains why protein misfolding can lead to diseases such as Alzheimer's?

Accepted Answer

Misfolded proteins can aggregate into insoluble fibrils that disrupt cellular function.

Question 14

Which of the following is NOT an advantage of cryo-electron microscopy (cryo-EM) for protein structure determination?

Accepted Answer

It works best for very small proteins below 10 kDa.

Question 15

Which of the following interactions is most important for driving the folding of a globular protein into its native conformation?

Accepted Answer

Hydrophobic interactions among nonpolar side chains.

Question 16

A protein contains a zinc finger motif. What is the most likely function of this motif?

Accepted Answer

Stabilizing DNA binding interactions by coordinating zinc ions with cysteine and histidine residues.

Question 17

Which of the following best describes the cooperative nature of protein denaturation?

Accepted Answer

Denaturation of one part of the protein increases the likelihood that neighboring regions will also denature.

Question 18

Which of the following statements about protein families is correct?

Accepted Answer

Protein families are groups of proteins with similar folding patterns and often similar functions.

Question 19

Which of the following is a function of protein disulfide isomerase (PDI) in protein folding?

Accepted Answer

It catalyzes the formation and rearrangement of disulfide bonds to assist in proper protein folding.

Question 20

A protein is found to have a Rossmann fold. This structural motif is most commonly associated with:

Accepted Answer

Binding nucleotides such as NADH.

Protein Structure Determination and Folding: Study Notes for Biochemistry

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