They project outward from the backbone at every $$C_b$$ atom.

A $$b-$$helix with an amphipathic character

Question 1

Which feature of the peptide bond is primarily responsible for its planarity in protein secondary structure?

Accepted Answer

Partial double bond character due to resonance

Question 2

In an $$b-$$helix, which atoms participate in the main stabilizing hydrogen bond?

Accepted Answer

The backbone N-H of residue $$i$$ and the backbone C=O of residue $$i+4$$

Question 3

Which of the following statements about the Ramachandran plot is correct?

Accepted Answer

It predicts sterically allowed conformations of the peptide backbone based on $$c$$ and $$c$$ angles.

Question 4

What is the typical number of amino acid residues per turn in an $$b-$$helix?

Accepted Answer

$$3.6$$

Question 5

Which amino acid is most likely to introduce a destabilizing kink in an $$b-$$helix?

Accepted Answer

Proline

Question 6

Why are cis-peptide bonds rare in proteins, except for those involving proline?

Accepted Answer

Steric hindrance from side chains makes cis-peptide bonds unfavorable.

Question 7

Which of the following best describes the orientation of side chains in an $$b-$$helix?

Accepted Answer

They project outward from the backbone at every $$C_b$$ atom.

Question 8

A segment of a protein has hydrophobic residues every 3-4 amino acids. What is the most likely secondary structure and its property?

Accepted Answer

A $$b-$$helix with an amphipathic character

Question 9

Which of the following is a consequence of the helical dipole in an $$b-$$helix?

Accepted Answer

The N-terminus is partially positive and interacts with negative charges or dipoles.

Question 10

Which of the following best explains why the peptide bond has restricted rotation?

Accepted Answer

It has partial double bond character due to resonance.

Question 11

If a protein segment has consecutive residues with similar $$c$$ and $$c$$ angles, what is the likely result?

Accepted Answer

Formation of a regular secondary structural element

Question 12

Which of the following is NOT a stabilizing interaction for an $$b-$$helix?

Accepted Answer

Disulfide bonds between backbone atoms

Question 13

What is the helical rise per residue in an $$b-$$helix?

Accepted Answer

$$1.5\ \mathrm{b}$$

Question 14

Which of the following is true about the geometry of the peptide bond?

Accepted Answer

It is sp$$^2$$ hybridized and trigonal planar.

Question 15

A mutation replaces an alanine with a proline in the middle of an $$b-$$helix. What is the most likely effect?

Accepted Answer

The helix will be destabilized and may develop a kink.

Question 16

Which enzyme catalyzes the interconversion of cis and trans proline peptide bonds?

Accepted Answer

Peptidyl prolyl isomerase

Question 17

Which of the following is a correct description of protein tertiary structure?

Accepted Answer

The overall 3D structure formed as secondary structural units pack together

Question 18

Which of the following is a property of amphipathic $$b-$$helices?

Accepted Answer

Hydrophobic side chains are clustered on one side of the helix.

Question 19

Which of the following is true about the formation of secondary structural elements in proteins?

Accepted Answer

They are formed when several consecutive residues participate in main-chain hydrogen bonds.

Protein Secondary Structure: The α-Helix (Biochemistry I Study Notes)

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