Chapter 16 - Taxonomy and Evolution Flashcards
When did cells first appear?
3.8 billion years ago
Early Earth was like what?
Extremely hot, (anoxic), with reduced organic, inorganic chemicals in abundance.
RNA World
a hypothetical stage of evolution, where self-replicating RNA molecules proliferated before the evolution of DNA and proteins.
Initial Cell Electron Transfer System
Likely primitive, through just one carrier but still allowed for development of a proton motive force to conserve energy.
What happened as Chemolithoautotrophs proliferated?
Organic material would accumulate in the environment, providing conditions needed for development of chemoorganotrophic organisms
What did new chemoorganotrophic organisms do?
They lead to oxidized organic compounds, with their more negative redox potential and increased number of electrons - likely leading to lengthened electron transport chains - resulting in faster growth and speeding up diversity.
How long ago did cells with phototrophic pigments evolve?
3.5 billion
What did phototrophs initially utilize
anoxygenic phototrophy, utilizing sulfur products as an electron donor when performing CO2 fixation.
Stromatolites
Layered rocks that form when minerals are incorporated into thick mats of microbes, growing on water surfaces. Ancient stromatolites contain fossilized microbial mats made up of cyanobacteria-ike cells
How long ago did cyanobacterial ancestors evolve?
2.5-3.3 billion years ago
What did cyanobacterial ancestors evolve?
They developed oxygenic photosynthesis by acquiring two photosystems and the pigment chlorophyll a.
What did cyanobacterial ancestor evolution lead to?
Being able to utilize water as an electron donor, causing oxygen to accumulate in Earth’s atmosphere.
Great Oxidation Event
Cyanobacterial ancestors evolution to cause oxygen to fill atmosphere - changed types o metabolism possible, allowed for the use of oxygen as final electron acceptor.
Ozone shield
a layer around earth made of ozone (O3) and serves to block out much of the UV radiation from sun. Allowed for organisms to start inhabiting the surface of the planet, as opposed to ocean or soil.
How did Ozone shield develop?
As O2 was released into atmosphere, it was converted to O3 when exposed to UV light.
Endosymbiosis
Offers explanation for development of eukaryotic cells - the idea that a cell ingested another cell, a free-living bacterium, but did not digest it.
What did endosymbiont have?
capabilities that proto-euakaryotic cells lacked - such as ability for phototrophy (chloroplasts) or oxidative phosphorylation (mitochondria).
What happened after a period of time of endosymbiosis
The two cells became mutually dependent upon one another, with the endosymbiont becoming and organelle.
Endosymbiont
what’s engulfed
chloroplast came from what
cyanobacterial ancestor
mitochondria came from what
gram negative bacillus ancestor
Evidence of endosymbiosis
Mitochondria and Chloroplasts both have a single, circular chromosome, undergo binary fission separate from eukaryotic cell, have 70s sized ribosomes, lipid bilayer with a 2:1 ratio of protein to lipid, have rRNA sequence that place them phylogenetically with bacteria.
Phylogeny
Reference to the development of an organism evolutionarily
What do molecular techniques that assess organisms genomes utilize?
ribosomal RNA (rRNA) nucleotide sequences - which provides most accurate information about the relatedness of microbes
What is Nucleic acid hybridization? (DNA-DNA hybridization)
commonly used tool for molecular phylogeny. Compares similarities between genomes.
How does Nucleic acid hybridization (DNA-DNA hybridization) work?
Genomes of two organisms are melted to separate complementary strands, and then allowed to cool down. Strands that have complementary base sequences will re-anneal.
Nucleic acid sequencing
use rRNAs from small ribosomal subunits, allowing direct comparison of sequences.
Why ribosomal sequences?
Idea because the genes encoding do not change very much over time, nor strongly influenced by horizontal gene transfer.
Molecular chronometer
aka way to track genetic changes over a long period of time, even between closely related organisms.
Last universal common ancestor (LUCA)
Root of phylogenetic tree, last common ancestor for organisms being compared
Node
branchpoint - organisms diverged
length of branch
amoutn of molecular changes over time
external nodes
specific taxa or organisms (although they can represent specific genes)
clade
group of organisms that have a particular ancestor in common
taxonomy
organization of organisms based on relatedness
phenetic classification
Classification that relies on phenotypes (physical appearance) of organisms
phylogenetic classification
Classification that relies on evolutionary relationships of organisms
genotypic classification
Classification that compares genes or genomes between organisms
polyphasic approach
most popular - combines all three types of classification
microbe species
No current species definition. The most commonly used is one that relies on both genetic and phenotypic information with a threshold of 70% DNA-DNA hybridization and 97% 16s DNA sequence identity needing to be present for two organisms to be deemed as same species.
