Type 2 T-independent

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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

Can occur independently in isolation

#Id: 7686

#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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#Unit 1. Molecules and their Interaction Relevant to Biology

                                                               Helix-turn-Helix

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#Unit 1. Molecules and their Interaction Relevant to Biology

                                                       Zinc Finger Motif

Zinc atom stabilizes the structure/fold by coordination bonds

Each motif contains about 30-50 amino acids

Contains regular patterns of Cys / His, which coordinate with Zinc atom

Contains one helix and two small anti-parallel beta sheets in each finger

Zinc holds helix and beta-sheets together

Helix binds to DNA

#Id: 7689

#Unit 1. Molecules and their Interaction Relevant to Biology

                                         Zinc Finger Motif