What did Günter Wächterhaüser do?
His development of the IRON-SULFUR WORLD THEORY and concept of “surface metabolism” (on iron pyrite for ex) has been important in the quest to deduce the evolution of the first cells from biochemical reactions on the ancient earth
What did Carl Woese do?
He developed a phylogenetic classification system using the sequence of the 16 S (18S in eucaryotes) rRNA genes which are highly conserved and found in ALL cells
Why were bacteria and archea placed together in the Monera?
Monera= single-celled procaryotic organisms
- but it is also difficult to striclty define single-celled
- Thus, it was mostly becasue neither were observed to be eucaryotic
What is the discovery that stimulated the inevitable chage?
Archea
The finding that archea are distinct from bacteria proved the monera to be an artificial taxon and threw everything else into question
- But also provided tools to discover natural taxonomy
- neither the five kingdom system nor the procaryotic eucaryotic dichotomy could account for the archeabacteria (archea)
- Interest in the “archeabacteria” and how they might be related to other organism, resulted in the need for, and then the actual development of the proposal of the 3 domains
What is unifying vs not unifying definition?
- eucaryotes: possess a membrane bound nucleus => unifying definition
- Procaryotes do not possess a membrane bound ucleus=> NOT a nifying definition
- only taxonomically-relevant common characteristics can be used to proposed organisms are related
Describe Woeses’ universal pylogenetic tree
- distances on the tree correspond to molecular genetic relatedness
(groups close tegoeth on the tree have very few nucleotide differences (MUTATIONS) in their 16S rRNA genes - Relatively few mutations occured during the TIME since the groups diverged
16S/18S sequence comparisons reveal 3 clusters (DOmains)
- The sequence differences between the domains indicate they are distinct and diverged by billions of years ago
What is a mutation?
- Mutations cause DNA sequence differences between species
- Mutations happen at a low rate over time
- DNA sequence differences can be correlated with evolutionary distances and time
16S rRNA genes ?
- Molecular chronometer, present in all cells
- Slowly evolving due to highly conserved ribosome function
- secondary structure is critical to function
- Large enough to have sequence diversity
- Small enough to make DNA sequencing practical at the time
