The confirmation of peptic group

Question 1

What is the structure that links amino acids in a polypeptide chain?

Answer 1

Peptide group

The two atoms involved in the peptide bond, along with their four substituents (the carbonyl oxygen atom, the amide hydrogen atom, and the two adjacent alpha-carbon atoms), constitute the peptide group.

Question 2

What are the two possible conformations of the peptide group?

Answer 2

Trans or cis

The conformation of the peptide group is restricted to one of two possible conformations, either trans or cis.

Question 3

Why is the trans conformation more favorable than the cis conformation?

Answer 3

Due to steric interference between side chains

The cis conformation is less favorable than the extended trans conformation because of steric interference between the side chains attached to the two alpha-carbon atoms.

Question 4

What restricts the free rotation around the N-Ca and Ca-C bonds in proteins?

Answer 4

Steric interference between main-chain and side-chain atoms

Rotation around the N-Ca and Ca-C bonds is restricted by steric interference between main-chain and side-chain atoms of adjacent residues.

Question 5

What is the actual structure of a peptide bond best represented as?

Answer 5

A hybrid of two resonance forms in which electrons are delocalized over the carbonyl oxygen, the carbonyl carbon, and the amide nitrogen. Rotation around the C-N bond is restricted due to the double-bond nature of the resonance hybrid form.

Figure 4.6 shows planar peptide groups in a polypeptide chain.

Question 6

What are the two conformations of a peptide group?

Answer 6

Trans and cis. Nearly all peptide groups in proteins are in the trans conformation, which minimizes steric interference between adjacent side chains.

Figure 4.7 illustrates trans and cis conformations of a peptide group.