Microbial Systematics Flashcards
What is the understanding for the origin of eukaryotes (evolution)?
endosymbiosis hypothesis
What is the endosymbiosis hypothesis?
the hypothesis that supports that the origin of mitochondria and chloroplasts were from a symbiotic association (engulfing) of prokaryotes with another cell
Who first formulated the endosymbiont hypothesis?
Lynn Margulis (previously, Lynn Sagan), an English scientist
Which scientist famously disagreed with Lynn Margulis’s hypothesis of endosymbiotic origin of eukaryotes? what did he do?
Carl Woese
he developed the 16S rRNA method of sequencing bacterial genomes/phylogenetically categorizing prokaryotes
How did Woese, inadvertently, contribute to Margulis’s endosymbiont hypothesis?
he disagreed, but the 16S rRNA method ended up being the best evidence to support Margulis’s hypothesis
What are the 2 hypotheses of the endosymbiont origin of eukaryotes?
eukaryotic cells originated containing a nucleus and endosymbiosis to attain mitochondria and chloroplasts occurred later
eukaryotic cells came from an intracellular association of an O2-consuming bacterium into an Archaeal host to produce the mitochondria
On a basic phylogenetic tree, how are bacteria, eukarya, and Archaea related?
from some unknown ancestor, bacteria and archaea split off
from the archaea branch, eukaryotes split off
= eukarya are more closely related to archaea than bacteria
What do both hypotheses of endosymbiosis suggest about the eukaryotic cell?
it’s chimeric (origins from both Archaea and Bacteria)
What supports the suggestion that eukaryotic cells are chimeric?
eukaryotes have lipids and metabolisms close to bacteria
eukaryotes have transcription and translational machinery close to Archaea
What did Woese contribute to phylogenetic studies in 1970s?
the use of 16S rRNA to
establish that prokaryotes are actually bacteria and archaea (not monophyletic)
create a universal framework for studying bacterial phylogeny
Why did Woese choose the 16S ribosomal subunit of RNA?
it was practical and plays a key role in bridging the functions of both subunits
it’s in the small subunit with 20s which binds mRNA
Describe the ribosomal RNA subunits
large subunit: 23s and 5s
small subunit: 16s + proteins
What makes small subunits of rRNA ideal for studying phylogeny?
they are in all domains of life
in all domains, they have the same function
they evolve slowly (are conserved)
they have enough nucleotides to study and determine reasonable significant differences
What is the small rRNA subunit in prokaryotes? eukaryotes?
pro: 16S rRNA
euk: 18S rRNA
When looking at the nucleotide sequence of a small rRNA subunit, what do the V regions mean? what are the white regions?
V = variable, indicate different prokaryotes
white regions are the conserved, essential regions that make prokaryotes prokaryotes
What is phylogeny?
the estimated evolution of organisms predicted from nucleotide sequencing
What is the universal phylogenetic tree based on?
SSU rRNA genes
Approx how many phyla are in bacteria according to Bergey’s manual?
24
What is LUCA?
the origin of life, the unknown ancestor of bacteria, archaea and eukarya
Pre-Darwinian evolution
How many phyla of Archaea in Bergey’s?
2
Crenarchaeota
Euryarchaeota
How many phyla of Eukaraya in Bergey’s?
How many phyla of Bacteria are known? (not just in the bergey’s)
there’s 80 known
Are most of the bacteria phyla cultured or uncultured?
most are uncultured and just defined by environmental sequences
What does it mean for bacteria to be phenotypically diverse?
physiology and phylogeny not necessarily linked