Friday, July 20, 2007

The Tree of Life

Bacteria - Traits

  • single, circular chromosome
  • Contain operons Many of the genes in E. coli are always turned "on". Others, however, are active only when their products are needed by the cell, so their expression must be regulated.
  • Do not have Introns: This is the portion of a gene that is transcribed into RNA but is removed during the formation of the mature RNA molecule. Found in rRNA and tRNA genes as well as in genes encoding proteins. Most eukaryotic genes have introns; most genes in bacteria and archeans do not.
  • bacterial-type membrane transport channels
  • Many metabolic processes including:
  1. energy production
  2. nitrogen-fixation
  3. polysaccharide synthesis

Eukaryotic Features

DNA replication machinery
histones are the chief protein components of chromatin. They act as spools around which DNA winds, and they play a role in gene regulation.
nucleosome-like structures

  • Transcription machinery
    RNA polymerase
    TATA-binding protein (TBP)
  • Translation machinery
    initiation factors
    ribosomal proteins
    elongation factors
    poisoned by diphtheria toxin

Conclusions from this collection of traits

Many traits found in the bacteria first appeared in the ancestors of all the present-day groups.
The split leading to the archaea and the eukaryotes occurred after the bacteria had gone their own way.
However, the acquisition by eukaryotes of mitochondria (probably from an ancestor of today's rickettsias) and chloroplasts (from cyanobacteria)occurred after their line had diverged from the archaea.

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