Q: Which equation correctly represents the calculation of the total dipole moment of an $\alpha$-helix with $n$ residues?

$\text{Total dipole} = n \times 3.5~\text{Debye}$

Question 1

Which statement best defines the primary structure of a protein?

Accepted Answer

The sequence of amino acids covalently linked to form a polypeptide chain.

Question 2

Which bond in the protein backbone is most responsible for restricting rotation and planarity?

Accepted Answer

The peptide (amide) bond

Question 3

Which pair of torsion angles in the protein backbone are flexible and help determine secondary structure?

Accepted Answer

$\phi$ (N–C\alpha) and $\psi$ (C\alpha–C)$

Question 4

What is the main stabilizing force in both $\alpha$-helices and $\beta$-sheets?

Accepted Answer

Hydrogen bonding between backbone atoms

Question 5

Which feature distinguishes an anti-parallel $\beta$-sheet from a parallel $\beta$-sheet?

Accepted Answer

Anti-parallel $\beta$-sheets have straight and more favorable hydrogen bonds.

Question 6

A Ramachandran plot is used to:

Accepted Answer

Visualize the allowed values of $\phi$ and $\psi$ angles in protein backbones.

Question 7

Which equation correctly represents the calculation of the total dipole moment of an $\alpha$-helix with $n$ residues?

Accepted Answer

$	ext{Total dipole} = n 	imes 3.5~	ext{Debye}$

Question 8

Which amino acid substitution is considered conservative?

Accepted Answer

Replacing a leucine with an isoleucine

Question 9

In an $\alpha$-helix, the hydrogen bond forms between the carbonyl oxygen of residue $i$ and the amide hydrogen of which residue?

Accepted Answer

$i+4$

Question 10

Which of the following is NOT a function of proteins in cells?

Accepted Answer

Storing genetic information

Question 11

Which secondary structure is most likely to be found in the allowed region of a Ramachandran plot with $\phi \approx -57^\circ$ and $\psi \approx -47^\circ$?

Accepted Answer

Right-handed $\alpha$-helix

Question 12

Which statement about the peptide bond is TRUE?

Accepted Answer

It is planar due to resonance stabilization.

Question 13

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

Accepted Answer

The association of two or more folded proteins into a multi-subunit complex.

Question 14

Which of the following is a consequence of the helix dipole in an $\alpha$-helix?

Accepted Answer

The amino terminus is partially positive and the carboxyl terminus is partially negative.

Question 15

Which method is commonly used to identify homologous proteins based on sequence alignment?

Accepted Answer

BLAST (Basic Local Alignment Search Tool)

Question 16

Which of the following statements about protein evolution is correct?

Accepted Answer

Proteins with many important amino acids evolve slowly.

Question 17

Which structural feature is shared by both $\alpha$-helices and $\beta$-sheets?

Accepted Answer

They are stabilized by hydrogen bonds between backbone atoms.

Question 18

Which of the following is TRUE about connectors between secondary structure elements in globular proteins?

Accepted Answer

They often consist of loops or turns that change the direction of the polypeptide chain.

Question 19

Which scenario best illustrates a multi-step application of protein structure concepts: A mutation changes a glycine to a proline in the middle of an $\alpha$-helix. What is the most likely effect?

Accepted Answer

The $\alpha$-helix will be disrupted because proline cannot form the necessary backbone hydrogen bonds.

Protein Primary and Secondary Structure: Foundations and Analysis

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