Evolution III - Evolution: a molecular perspective Common...

Info iconThis preview shows pages 1–14. Sign up to view the full content.

View Full Document Right Arrow Icon
Evolution: a molecular perspective Common descent verified by the DNA code Does the genetic code itself shows signs of natural selection? Neutral mutations and the molecular clock. Making trees from molecular sequences. Where do new genes come from?
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Discovery of the double helical structure of DNA Watson and Crick (with help from X- ray crystallographic data from Franklin) predict the structure of DNA. Eventually, it is clear that all organisms use the same (more or less) genetic code. James Watson Francis Crick 1928-- 1916-2004 Nobel Prize--1962 Rosalind Franklin 1920-1958
Background image of page 2
The nature of the genetic code and the necessity of an adapter molecule Crick suggested that with 4 different nucleotides coding for 20 amino acids there had be a code where more than one nucleotide was “read” for each amino acid. He suggested 3 nucleotides per amino acid , giving 64 possible codons. Crick also suggested the need for an adaptor between each amino acid and the DNA sequence encoding it (later discovered to be transfer RNA).
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
tRNA molecules bring in each amino acid to the elongating protein chain http://www.ict-science-to-society.org/Pathogenomics/images/central_dogma.gif
Background image of page 4
Is there a “logical” relationship of the codons to each other or to the amino acids that they encode? Or is the genetic code organized randomly? http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/graphics/GP.GeneticCode.GIF
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
T =
Background image of page 6
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The genetic code is not organized randomly: it is organized so that… Changes of one nucleotide will tend to result in: 1) the same amino acid 2) a biochemically similar amino acid. Natural selection has acted on the genetic code to minimize the effects of mutations on the amino acid sequence of proteins!!!!
Background image of page 8
Codon bias Suppose an organism has 3 copies of one tRNA (GUU), 5 copies of another tRNA (GUC), 2 copies of another tRNA (GUA), and 8 copies of another tRNA (GUG) all of which code for valine. At the level of the DNA, the most frequently used codon for valine will be GUG, especially in an abundant protein. 3 copies 5 copies 2 copies 8 copies
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Natural selection has influenced how proteins are encoded in subtle ways Codon bias: Each codon is represented by a tRNA. In each species, there may be more copies in the genome of some tRNAs than others. Natural selection favors the codon with the most tRNAs. Energetics: The “cost” to the cell for each amino acid varies (some are taken up by high affinity pumps, others are synthesized). Proteins (especially highly abundant proteins) tend to use the “cheapest” amino acids.
Background image of page 10
Is all evolution via natural selection? No. Evolution can occur via genetic drift as a result of neutral evolution. This is especially true in small populations that are evolutionary “bottlenecks.”
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Selectionism vs. neutralism On the molecular level, most change is neutral. On the organismal level (which is the level on which natural selection acts) more of the change is subject to natural selection.
Background image of page 12
Most mutations arise during DNA replication.
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 14
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/28/2012 for the course BIO 49593 taught by Professor Wanser during the Spring '10 term at University of Texas at Austin.

Page1 / 65

Evolution III - Evolution: a molecular perspective Common...

This preview shows document pages 1 - 14. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online