Introduction Flashcards
Robert Hooke
- micrographia 1665
- first observations of microbial spores under a microscope
- 300x magnification
Louis Pasteur
- germ theory of life, proved microbes were responsible for decomposition
- 1822-1895
Robert Koch
- first linked cholera pandemic to cholera bacteria
- Koch’s postulus = steps needed to connect specific microbe to disease including infecting a healthy person with microbe
- 1843-1910
how are prokaryotes different to eukaryotes
- no membrane bound organelles
- pili
- 70s ribosomes (eukaryotes have 80s)
- flagella (smaller)
- some have gas vesicles/ endospores
- nearly all have a cell wall, different from eukaryote cell walls
- no mitochondria or ER
- no cytoskeleton/microtubules
Carl Woese
- used ribsosomal RNA to identify third domain of life, Archaea
‘unseen majority’
<1% microbes can be grown on agar media
phylogenomics
comparing whole genomes
monophyletic groups
- natural grouping of organisms with one common ancestor
- usually categorised by synapomorphies
archaea vs bacteria
- bacteria have peptidoglycan cell walls, archaea cells walls contain various polysaccharides, proteins, or glycoproteins
- the amino acid initiator for tRNA is formylmethionine in bacteria and methionine in archaea and eukarya
- RNA polymerase in archaea is more similar to eukaryotes
- bacteria have lipids in cell membrane
why sequence rRNA?
- all organisms have ribosomes inherited from last universal common ancestor
- evolves slowly
- same role in all organisms
properties of archaea
- none are pathogens
- usually extremophiles
- obligate anaerobes
- usually uncultured
- some methanogens or involved in nitrification
origin of eukaryotes
- endosymbiosis of mitochondria from alphaproteobacteria
- most of bacterial DNA merged into main host nucleus
- host cell probably archaea
metagenomics
analysis of genomes in a bulk sample e.g. sediment sample to analyse communities of microorganisms
Lokiarchaeota
- archaea from Loki’s castle, deep ocean sediment in the Arctic ocean
- nearest eukaryotic relative
- had eukaryotic features related to cell function including a cytoskeleton with microtubules, genes relating to protein degradation and ER
Asgard archaea
- relative of Lokiarchaea
- proposed common ancestor of eukaryotes
- Hiroyuki Imachi cultured it
great oxygenation event
- 2.1bya evolution of photosynthesising cyanobacteria
- 1.6bya endosymbiosis of chloroplast in marine eukaryotes
- evolution of aerobic metabolism (mitochondria) and meiosis (probably linked) driven by a rise in O2
- colonisation of land
HGT in bacteria
- transformation from lysis
- conjugation from pili
- transduction from virus
inter-kingdom HGT
e.g. Agrobacterium tumefaciens
- interdomain HGT (prokaryote to eukaryote)
- transfers Ti plasmid into host nucleus
- triggers tumour growth in plant host, crown galls
- used to GM plants
transposable genetic elements
‘junk’ DNA (40% of human genome) derived from retrotransposon DNA, stabilised into non-coding DNA
retrotransposon DNA
- mobile genetic elements that can move about independent of meiosis/mitosis and can replicate after excision from genome
- encoding genes for transposition with long terminal repeats (LTRs) on either end
- closely related to retroviruses as it is copied from RNA to DNA using reverse transcriptase (unusual retroviral property)
euryarchaea
closest archaea to eukarya
