Omega loop

Beginning and end of the loop come together

The shape appears similar to Greek Capital Omega

Compact Globular structure

No regular repeating pattern of hydrogen bonds

Side chains pack into the center of the loop

Omega loops have specific functions like

Omega loop from two proteins interact with each other to form dimers

Phosphate binding loop of nucleotide proteins

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#Unit 1. Molecules and their Interaction Relevant to Biology

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#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.

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#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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#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

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#Unit 1. Molecules and their Interaction Relevant to Biology

                                                                        Helix-turn-Helix

Two helices are connected by a small loop or turn

These helices are stabilized by non-polar contacts between the helices

Mostly found in DNA binding proteins, directly involved in DNA binding

Generally consists of 20 amino acids

Second helix is involved in DNA binding, enters in major groove of the target site

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                                                               Helix-turn-Helix