ENZYMES-2

Protein structure

Dipeptide

Polypeptide

Tripeptide

Tetrapeptide

Pentapeptide

Oligopeptide

SINGLE BOND

DOUBLE BOND

It do not allow free rotation of functional

attached to it

It allow free rotation of functional attached to it

Single bondSi

ngle

bon

d

Partial Double bond

• C and N atoms participate in a π bond.

• Which makes lone e- pair on the oxygen.

• There is no free rotation around C-N bond (Peptide bond).

Consequences of Peptide bond as Partial double bond

1. It restricts free rotation around the peptide bond

2. Six atoms of peptide bond forms amide plane.

3. C−N bond length -----------------> 0.133 nm Normal C−N bond lengths------> 0.145 nm Typical C=N bonds----------------> 0.125 nm

4. The peptide bond is estimated to have 40% double-bond character.

Protein Multimeric Homomultimeric

Heteromultimeric

Monomeric

Protomer

Primary Structure

Secondary structure

α-Helixβ-Sheet

STERIC HINDERENCE

STERIC HINDERENCE

STERIC HINDERENCE

STERIC HINDERENCE

Ramachandran Plot

It show the distribution of allowed values in a protein or in a family of proteins.

α-Helix

1. One turn of the helix represents 3.6 a.a. residues.

2. Each amino acid residue extends 1.5 Å3. With 3.6 residues per turn i.e. 3.6 × 1.5 Å = 5.4 Å

This is translation distance/pitch 4. All H-bonds are parallel to helix5. All the carbonyl groups points in one direction6. N-H groups are pointing in the opposite

direction.

Each peptide bond have dipole moment.

Dipole moment is because of N-H and C=O

Such groups lie as helix axis.

Therefore Helix has dipole moment.

N-terminus have partial positive charge & C-terminus have partial negative charge.

β-Sheet

0.347 nm

0.325 nm

• H bonds in this structure are interstrand (not intrastrand)

• Parallel sheets are large(more than five strands).

• Antiparallel sheets have few strands (not more than two)

Hydrophobic side chains

Hydrophobic side chains

Hydrophobic side chains

β-turn

β-turn

Tertiary structure

THE END