7. Taxonomy Flashcards
HGT (Horizontal Gene Transfer)
HGT (Horizontal Gene Transfer): exchange of genetic material between cells.
first RNA
then DNA
finally 3 part system(DNA,RNA ,Protein) evolved
First self-replicating system may have been RNA-based (RNA world theory):
– RNA can bind small molecules(e.g. ATP, other nucleotides).
– RNA has catalytic activity; may have catalyzed its own synthesis (Ribozymes).
– RNA can be copied like DNA.
Last universal common ancestor (LUCA)?
Last universal common ancestor (LUCA): population of early cells from which cellular life may have diverged into ancestors of modern-day Bacteria and Archaea.
As early Earth was anoxic, energy-generating metabolism of primitive cells was aerobic/ anaerobic? and chemoautotrophic/chemolithotroph?
exclusively anaerobic and likely chemoautotrophic.
- Carbon source: CO2;
- Energy and electrons source: H2
origin of cellular life
- Early forms of chemoautotrophic and photoautotrophic metabolism supported production of large amounts of organic compounds.
- Organic material stimulated evolution of various chemoheterotrophic metabolisms
mutation
adaptive mutation vs. silent mutation
mutation is a change in the genome of an organism (nucleotide change, insertion, deletion).
– Adaptive mutations: improve fitness of an organism, increasing survival in its
environment.
– Silent mutations: may be beneficial in other environments allowing the microorganism to colonize new niches.
Gene duplication, gene loss and horizontal gene transfer
-acquisition of a whole new gene from another organism
Genetic change may be silent, deleterious or beneficial
(new function or change in activity).
Phylogenetic: Sequencing ribosomal RNA Carl Woese (1970s):
Carl Woese (1970s):
– Sequencing of the small subunit rRNA (SSU rRNA):
16S rRNA in prokaryotes, 18S rRNA in eukaryotes.
– Established the presence of 3 domains of life: Bacteria, Archaea, and Eukarya
– Provided a unified phylogenetic framework for Bacteria
mutations determines similarity of 2 species
- The evolutionary relationship between two organisms is directly correlated to the number of mutation that have accumulated in each one.
»Few differences: closely related
»Many differences: diverge a long time ago
Phylogenetic: Sequencing ribosomal RNA
- PCR?
- Sequence 16S rRNA
- Align sequences (to take into account insertion /deletion)
insertion: add
–> nucleotides and changes the whole sequences
» compares the difference between sequences from different species
»more differences, less similarity in these species.
- PCR: polymerized chains reaction
eukaryotic cell is phylogenetically closer to___?
Archea
Two hypotheses exist to explain the formation of the eukaryotic cell:
- nucleus formation before endosymbiosis
Eukaryotes began as a nucleus-bearing lineage that later acquired mitochondria and chloroplasts by endosymbiosis - nucleus formation after endosymbiosis
Eukaryotic cells arose from intracellular association between a H2-producing bacterium (the symbiont), which gave rise to mitochondria, and an H2- consuming archaeal host. The archaeal host later developed a nucleus.
Multilocus sequence typing (MLST)
several different “housekeeping genes” from a species are sequenced and aligned to the respective sequences of other individuals of the same species.
- Has sufficient resolving power to distinguish between very closely related strains.
- Identification
Identificaiton of an unknown microorganism will depend on the comparison of its properties with those of organisms that have already been classified and name (Type strains).
- Identificaiton of an unknown microorganism will depend on the comparison of its properties with those of organisms that have already been classified and name (Type strains).– Morphology
– Biochemical proper>es
– 16S rRNA sequencing. – MLST - Dichotomous key (morphology and phenotype)
- Serotyping
