James Hutton and Charles Lyell – Uniformitarianism

Darwin was greatly influenced by Lyell’s teachings, and he adopted uniformitarianism in his thinking about evolution.

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#Unit 1. Molecules and their Interaction Relevant to Biology

The 3¹⁰ helix has 3 residues per tum and contains 10 atoms between the hydrogen bond donor and acceptor, hence its name.

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#Unit 1. Molecules and their Interaction Relevant to Biology

Both the pi helix and the 310 helix occur rarely and usually only at the ends of a helices or as single-tum helices. They are not energetically favorable, since the backbone atoms are too tightly packed in the 310 helix and so loosely packed in the n helix that there is a hole through the middle. 

Only in the a helix are the backbone atoms properly packed to provide a stable structure.

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#Unit 1. Molecules and their Interaction Relevant to Biology

Right-handed helical conformation has 3.6 residues per turn and 1.5A/aa.

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#Unit 1. Molecules and their Interaction Relevant to Biology

In the α helix, the backbone hydrogen bonds are arranged such that the peptide CO bond of the nth residue points along the helix axis toward the peptide NH group of the (n + 4)th residue. 

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#Unit 1. Molecules and their Interaction Relevant to Biology

This results in a strong hydrogen bond that has the nearly optimum N…O distance of 2.8 A.

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#Unit 1. Molecules and their Interaction Relevant to Biology

In a typical a-helix of 12 (or n) residues, there are 8 (or n-4) hydrogen bonds.