Microbial Evolution and Taxonomy Flashcards
How old is the Earth?
~4.5 billion years old
When did water appear in liquid form?
~4.3 bilion years ago
When did microbial life begin?
~4.2 billion years ago
What are Stomatolites?
fossilized microbial mats - really thick layers of bacteria
How old are Stomatolites?
3.5 billion years old
Of what were ancient stromatolites made?
anoxygenic phototrophic filamentous bacteria
What is the Surface Origin Hypothesis?
- first membrane, self-replicating cells arose out of primordial soup rich in organic and inorganic compounds in ponds
- Against this hypothesis:
- dramatic temp flunctuations
- mixing from meteor impacts
- dust clouds
- storms
What is the Subsurface Origin Hypothesis?
- Life originated at hydrothermal springs on ocean floor
- conditions would have been more stable
- steady and abundant supply of energy (H2 and H2S) may have been available
What is the order in which biological entities formed?
- simple molecules
- hydrocarbons, sugars, fatty acids, amino acids, peptides, nitrogen bases
- RNA life
- RNA and proteins
- DNA
- LUCA - last universal common ancestor
- Diversification of molecular biology, lipids and cell wall structure
- early bacteria and early archaea
- Dispersal to other habitats
What is the RNA World Theory?
- proposes that RNA was first nucleic acid
- RNA can bind small molecules
- RNA has catalytic activity, may have catalyzed own synthesis
- DNA eventually became the genetic norm
- b/c its more stable
Metabolism of Primitive Cells
- chemolithoautotrophic
- Carbon from CO2
- energy from H2
When did the LUCA btwn Bacteria and Archaea diverge?
~3.8 billion years ago
When did cyanobacteria begin to generate O2?
~2.7 billion years ago
What is the Great Oxidation Event?
accumulation of O2 concentration to 1 part per million
When did the Great Oxidation Event occur?
2.4 billion years ago
Why did the O2 take so long to accumulate?
O2 had to react w/ FeS and FeS2 first
also O2 was gobbled up as soon as made at first
When did Eukaryotes first appear?
~2 billion years ago
What is the “Other Hypothesis” regarding the origin of eukaryotes?
- eukaryotes began as nucleas-bearing lineage that late aquired mitochondria and chloroplasts by endosymbiosis
What is the Hydrogen Hypothesis?
- eukaryotic cell arose from engulfment of a H2-producing cell of Bacteria by a H2-consuming cell of Archaea
- made mitochondria
- later formed nucleus
- formed chloroplast by endosymbiosis
Why is the Hydrogen Hypothesis more likely than the “Other Hypothesis?”
- eukaryotes have similar lipids and energy metabolisms to bacteria
- eukaryotes have transcription and translational machinery most similar to archaea
Phylogeny
- evolutionary history of a group of organisms
- inferred from nucleotide sequence data
- Assumptions:
- all organisms evolved from the LUCA
- DNA sequences represent a record of the organism’s ancestry
Molecular Clocks (chronometers)
- certain genes and proteins that are measures of evolutionary change
- need to be…
- functionally constant
- sufficiently conserved
- suffient length
- found in all domains of life
- need to be…
- most widely used ones are small subunit rRNA (SSU rRNA)
- 16S rRNA or 18S rRNA
- Assumptions…
- mutations occur at constant rate
- mutations are neutral
- mutations are random
BLAST (Basic Local Alignment Search Tool)
- alignment algorithm to compare sequence of interest to known sequences in database
What is the bacterial origin of mitochondria and chloroplasts?
Mitochondria arose from Proteobactreia
Chloroplasts arose from Cyanobacteria
