Lecture 5: Peptide Bonds

Question 1

Formation of a Peptide bond

Answer 1

Type of Rxn: Condensation
Removes a water
Rxn is carried out by a catalytic RNA located in the ribosome
Amide bond: COO- & NH3+

Question 2

Characteristics of Peptide Bond

Answer 2

Planar
Hybrid of 2 resonance states
CN bond has partial double bond character
Rigid –> No free rotation
Trans configuration: avoid steric hindrance between R groups
Energy consuming

Question 3

Phi Bond Angle

Answer 3

Angle of rotation about bond between N and a-carbon

HN-CHR

Question 4

Psi Bond Angle

Answer 4

Angle of rotation about bond between carbonyl & a-carbon

RHC-CO

Question 5

Ramachandran Plot

Answer 5

Shows possible combinations of phi and psi angles to give structure to proteins
Upper left quadrant: dark green = beta sheet
Lower left quadrant: dark green = right handed a-helices
Upper right quadrant: light green = left handed a-helices