Refractory period is divided into:

Absolute refractory period

Relative refractory period

TLS Online TPP Program

#Id: 7679

#Unit 1. Molecules and their Interaction Relevant to Biology

Because they cannot rotate, each peptide bond holds 6 atoms in a plane.

However, most possible angles of Phi (φ) and Psi (ψ) are impossible due to clashes

between atoms. These balls are much smaller than the atoms they represent.

TLS Online TPP Program

#Id: 7680

#Unit 1. Molecules and their Interaction Relevant to Biology

TLS Online TPP Program

#Id: 7681

#Unit 1. Molecules and their Interaction Relevant to Biology

TLS Online TPP Program

#Id: 7682

#Unit 1. Molecules and their Interaction Relevant to Biology

In fig, Phi is fixed at 0º. Clashes occur at ALL Psi angles. Phi = 0º is physically

impossible.

TLS Online TPP Program

#Id: 7683

#Unit 1. Molecules and their Interaction Relevant to Biology

The Ramachandran Principle is that alpha helices, beta strands, and

turns are the most likely conformations for a polypeptide chain to 

adopt, because most other conformations are impossible due to

steric collisions between atoms. 

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#Id: 7685

#Unit 1. Molecules and their Interaction Relevant to Biology

Beta Hairpin

Two anti-parallel beta strands connected by a loop / turn, look like hairpin

Can occur independently in isolation