Question 1

Which of the following best describes the role of hydrogen bonds in the formation of protein secondary structure?

Accepted Answer

Hydrogen bonds form between the backbone amide and carbonyl groups, stabilizing alpha-helices and beta-sheets.

Question 2

A Ramachandran plot is used to visualize which of the following properties of a polypeptide chain?

Accepted Answer

The allowed values of backbone dihedral angles $$\phi$$ and $$\psi$$ for amino acid residues.

Question 3

Which statement about the alpha-helix is CORRECT?

Accepted Answer

The alpha-helix has a dipole moment due to the alignment of peptide bond dipoles along the helix axis.

Question 4

In the context of protein folding, what is the 'Levinthal's paradox'?

Accepted Answer

The discrepancy between the astronomical number of possible conformations and the rapid folding of proteins in nature.

Question 5

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

Accepted Answer

Hydrophobic side chains are buried in the protein core, minimizing their contact with water and driving the protein to fold into a globular shape.

Question 6

A protein is subjected to SDS-PAGE. What property of the protein primarily determines its migration through the gel?

Accepted Answer

Its molecular weight, as SDS denatures the protein and imparts a uniform negative charge.

Question 7

Which of the following amino acids is most likely to be found in a turn or loop region of a protein due to its ability to disrupt regular secondary structure?

Accepted Answer

Proline

Question 8

During ion exchange chromatography, how are proteins separated?

Accepted Answer

By their net charge, with proteins of opposite charge to the beads being retained and eluted by increasing salt concentration.

Question 9

Which of the following is a consequence of protein misfolding in cells?

Accepted Answer

Protein aggregation, which can lead to diseases such as Alzheimer's.

Question 10

What is the function of chaperone proteins in the cell?

Accepted Answer

They assist in the proper folding of other proteins and prevent aggregation.

Question 11

Which of the following best describes the 'molten globule' state in protein folding?

Accepted Answer

A partially folded intermediate with significant secondary structure but lacking a fully formed tertiary structure.

Question 12

Which of the following statements about disulfide bonds is TRUE?

Accepted Answer

Disulfide bonds stabilize protein structure by covalently linking cysteine side chains.

Question 13

A protein sample is analyzed by size exclusion chromatography. Which protein will elute first?

Accepted Answer

The largest protein, as it is excluded from the pores and travels the shortest path.

Question 14

Which of the following is a feature of the beta-sheet structure in proteins?

Accepted Answer

Beta-sheets are stabilized by hydrogen bonds between backbone atoms of adjacent strands.

Question 15

Which of the following best describes the concept of conformational entropy in protein folding?

Accepted Answer

The loss of entropy as a protein folds from a random coil to a more ordered structure.

Question 16

Which technique would you use to separate a protein based on its specific binding affinity to another molecule?

Accepted Answer

Affinity chromatography

Question 17

A protein is found to have a helical dipole moment. What does this mean?

Accepted Answer

The helix has a directional electric charge along its axis due to the alignment of peptide bond dipoles.

Question 18

Which of the following is a reason why some proteins do NOT fold properly in vivo?

Accepted Answer

Protein aggregates form due to heat shock or improper folding.

Question 19

Which of the following best describes the funnel analogy of protein folding?

Accepted Answer

Protein folding is guided by a landscape where many possible conformations narrow toward the lowest energy state.

Question 20

Which of the following statements about collagen is TRUE?

Accepted Answer

Collagen is a fibrous protein with a triple-helical structure stabilized by hydroxyproline and glycine residues.

Protein Structure, Folding, and Purification: Study Guide

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