lect 18 - eukaryotic evolution Flashcards
(19 cards)
2 components of DNA sequencing revolution
metagenomics
- sequencing all the DNA in an environment then piecing it together
single-cell genomics
- isolating single cells and sequencing genomes from them
the new tree of eukaryotes
these are so dynamic
most are single celled protists
many are completely new groups and/or relationships
its not known which groups are the most ancestral
lions of the microbial world
provora
— nibblers and hunters (as different as yeast and humans)
microbial predators form a new supergroup of eukaryotes
new ways of feeding
where did eukaryotes emerge from?
archaea
archaeal sister lineages of eukaryotes
bridges the gap between prokaryotes and eukaryotes
loki’s castle — hydrothermal vents between Norway and Greenland
— this was the first, but now found more
genomes of newly discovered archaea have many eukaryotic signature proteins
actin example
actin related genes and protein
organizing features of cell complexity
both prok and euk — thought to be only euk
study of first “Asgard” archaea to be cultured
japanese scientists
isolation of an archaeon at the prokaryote-eukaryote interface
growing for 13 years
- Prometheoarchaeum syntrophicum
— still a lot of evolution even tho part of sister lineage
sister lineages of eukaryotes
more complex than previously thought?
study 1: Loki’s castle — hydrothermal vents between Norway and Greenland
study 2: based on 55 conserved ribosomal proteins
study 3: actin example — always thought this was euk specific
— actin related genes and protein
study 4: first ‘Asgard’ archaea
Symbiogenic hypothesis of the origin of the eukaryotic cell
evidence: hybrid origin or genomes
- mitochondria evolved from bacterial symbiont
- chloroplast from cyanobacteria
• Massive acquisition of new genes & functions, metabolic potential, invasion of new niches (photosynthesis, respiration, etc..
— changed oxygen budgets - all about symbiosis
what is older, mitochondria or eukaryotes ?
there is not a single living eukaryote that didnt descend from an ancestor that had a mitochondrion
What is the evidence that mitochondria are descended from a bacterial symbiont?
they have their own genetic material clearly associated w bacterial origin
always have own separate genome clearly descended from bacteria
membrane bound
does the mitochondrion in all eukaryotes contain its own genome?
most eukaryote mitochondrion contain its a own genome, but NOT all
the mitochondrion contains genes from 3 different places:
encoded in the mitochondrial genome
of mitochondrial origin, but not encoded in the nuclear genome
encoded in the nuclear genome
components of mitochondrial genomes (5 points)
mito genomes are small
human mito genomes = 13 protein coding genes, 22 tRNAs, 2 rRNAs
the genes had massive gene loss and transfer to nucleus
mito proteome is much larger than mito genome — genes coming from nuclear genome and going into organelle
evidence for continual transfer — in form of functional genes and pseudogenes — MITO GENOMES ARE DYNAMIC
study of nuclear embedded mito DNA sequences in human genomes
lots of fragments coming from mito and going into nuclear genes
“Here we analyse whole-genome sequences from 66,083 people-including 12,509 people with cancer and demonstrate the ongoing transfer of mitochondrial DNA into the nucleus, contributing to a complex NUMT landscape. More than 99% of individuals had at least one of 1,637 different NUTs, with 1 in 8 individuals having an ultra-rare NUMT that is present in less than 0.1% of the population. More than 90% of the extant NUMTs that we evaluated inserted into the nuclear genome after humans diverged from apes. Once embedded, the sequences were no longer under the evolutionary constraint seen within the mitochondrion, and NUMT-specific mutations had a different mutational signature to mitochondrial DNA. De novo NUTs were observed in the germline once in every 104 births and once in every 103 cancers.’
do all euks have mito genome ?
no, a number of euks no longer have a mito genome
still hv organelle w some genes having mito origin (but now in nuclear genome)
these organisms are anaerobic and medically important pathogens and parasites for humans
Giardia lamblia
protist causes giardiasis (beaver fever)
was thoight to have no mito or homologous organelle. — but has mito with NO genome
Its nuclear genome contains genes of mitochondrial origin that localize to tiny organelles (called mitosomes)
— dont do aerobic respiration
How many eukaryotes are known that have completely lost their mitochondrion (genome AND organelle)?
JUST 1 — discovered in 2016
doesnt hv a mito genome or organelle
study: A Eukaryote without a Mitochondrial Organelle
— monocercomonoides
- an oxymonad protist isolated from chinchilla guts, is the first and only example of a eukaryote that has lost mitochondria entirely!
So why are there no known examples of eukaryotes that never had mitochondria?
1) They’re still waiting to be discovered
2) They went extinct
3) There is no such thing, because acquisition of mitochondria is the single act that gave rise to, and defines, eukaryotes
