Chapter 4 section 7

Question 1

What is the nature of the peptide bond?

Answer 1

It has partial double-bond character due to resonance between the C=O and C–N forms.

Question 2

How does peptide bond resonance affect rotation?

Answer 2

It restricts rotation around the C—N bond, keeping the amide group planar.

Question 3

What is the “amide plane”?

Answer 3

The six atoms of the peptide bond are coplanar, forming the amide plane of the polypeptide backbone.

Question 4

What are the rotational degrees of freedom in the peptide backbone?

Answer 4

Only around N—C𝛼 and C𝛼—C₀ bonds.

Question 5

How long is the C₀—N bond and what does it indicate?

Answer 5

0.133 nm, shorter than a normal C—N but longer than a C=N, indicating ~40% double-bond character.

Question 6

Why is the peptide bond polar?

Answer 6

Resonance creates partial charges on the carbonyl oxygen (δ⁻) and amide nitrogen (δ⁺).

Question 7

Why is the peptide bond considered to have partial double-bond character?

Answer 7

It is a resonance hybrid between a form with a C=O double bond and a form with a C=N double bond.

Question 8

How does this partial double-bond character affect rotation?

Answer 8

Rotation around the C₀—N peptide bond is restricted, keeping the bond planar.

Question 9

What is the hybrid nature of the peptide bond?

Answer 9

The actual bond is intermediate between single and double bonds, giving ~40% double-bond character.

Question 10

What gives the peptide bond its partial double-bond character?

Answer 10

Resonance between a form with a C=O double bond and a form with a C=N double bond.

Question 11

How does partial double-bond character affect the peptide bond?

Answer 11

It restricts rotation around the C₀—N bond, keeping the peptide bond planar.

Question 12

What is the hybrid nature of the peptide bond?

Answer 12

The bond is intermediate between single and double bonds.

Question 13

Why does the peptide bond have partial double-bond character?

Answer 13

Due to resonance between a C=O double bond form and a C=N double bond form.

Question 14

What effect does this partial double-bond character have?

Answer 14

It restricts rotation around the C₀—N bond and keeps the peptide bond planar.

Question 15

What is the hybrid nature of the peptide bond?

Answer 15

It is intermediate between a single bond and a double bond.

Question 16

What is the nature of the peptide bond in proteins?

Answer 16

It has partial double-bond character due to resonance between C=O and C=N forms.

Question 17

How does this resonance affect peptide bond rotation?

Answer 17

Rotation around the C₀—N bond is restricted, keeping the bond planar.

Question 18

What type of hybridization do the C₀ and N atoms have?

Answer 18

Both are sp² hybridized, contributing to planarity.

Question 19

Why does the peptide bond have partial double-bond character?

Answer 19

Because resonance exists between the C=O and C=N forms, making the bond intermediate between a single and double bond.

Question 20

What effect does this partial double-bond character have on rotation?

Answer 20

It restricts rotation around the C₀—N bond, keeping the peptide bond planar.

Question 21

What is the hybridization of the carbonyl carbon (C₀) and amide nitrogen in a peptide bond?

Answer 21

Both are sp² hybridized.

Question 22

What defines a protein?

Answer 22

A molecule composed of one or more polypeptide chains.

Question 23

What is a monomeric protein?

Answer 23

A protein made of a single polypeptide chain.

Question 24

What is a multimeric protein

Answer 24

A protein made of more than one polypeptide chain.

Question 25

What is a homomultimeric protein?

Answer 25

A multimeric protein with identical polypeptide chains.

Question 26

What is a heteromultimeric protein?

Answer 26

A multimeric protein with different polypeptide chains.