Photosynthetic Eukaryotes Flashcards
define bikont
evolved from cells with two flagella
define archaeplastida
plant; ancient chloroplast group
define unikont
evolved from cells with one flagella
how is photosynthesis so dispersed in unrelated lineages? two theories:
- Evolved independently multiple times - convergent evolution (ecologically good idea)
- Photosynthesis evolved only once in bacteria
in what organisms did photosynthesis evolve once? How do they occur?
- Cyanobacteria (blue-green algae) evolved photosynthesis found in eukaryotes (consumes water and produces oxygen)
- Bacteria that form chains of bacteria (even though prokaryotic)
how did eukaryotes acquire photosynthesis?
Eukaryotes acquired photosynthesis through endosymbiosis of cyanobacteria
Ancestral bikont eukaryotic cell engulfed a cyanobacteria (normally would be digested but cyanobacteria became an organelle - chloroplast!)
what three lineages diverged after primary endosymbiosis and how?
Three plantae lineages diverged after this point: glaucophytes, red algae and green algae (all chloroplasts are related)
Then eukaryotic green algae were ingested by chlorarachniophytes and euglenoids - causes photosynthesis in Cercozoa and Discicristates - 4 membranes (two from primary symbiosis, thirds from endosymbiont cell membrane and the fourth is the cercozoa host’s vesicle) and 1 nucleomorph between 2nd and 3rd membranes
Red algae was also ingested (secondary endosymbiosis) to cause other lineages with photosynthesis
There were tertiary and quaternary endosymbionts too!
describe the chloroplast membranes and genetic material
- Thylakoids (network of internal membranes)
- Double membraned - inner is remnant of cyanobacteria membrane and outer is remnant of membrane of the vesicle that the eukaryote used in phagocytosis
- Has now exchanged genetic information with the eukaryotic host
Some bacterial genes are now in the nucleus and are expressed in the nucleus to make proteins for the chloroplast (codependence)
how might this original photosynthetic event taken place? Model species protist vorticella
Model species protist vorticella grazes on Chlorella (green algae)
Digestion is slow (might take a month for chlorella to die and be digested)
Photosynthesising during that month (receive nutrients inside the vorticella and vorticella gets carbohydrates) - proto-endosymbiotic relationship
what was the second event of primary endosymbiosis?
Independent case in paulinella chromatophora (cercozoa)
Derived from a different group of cyanobacteria
Gene transfer has occurred (codependence)
Chloroplast genome is larger in this case than in the first event
Likely to have occurred 60 million years ago
when did primary and secondary endosymbiotic events occur?
Independent case in paulinella chromatophora (cercozoa)
Derived from a different group of cyanobacteria
Gene transfer has occurred (codependence)
Chloroplast genome is larger in this case than in the first event
Likely to have occurred 60 million years ago
how can we tell that photosynthesis evolved just once?
Look at chloroplast genomes from different eukaryotic linages and they have a very similar structure (came from a common ancestor)
Inverted repeat (segments that have been duplicated and reinserted in the opposite direction) is found in all chloroplasts of all photosynthetic eukaryotes
The nuclear genomes are not similar between lineages but chloroplast genomes are!
non-eukaryotic photosynthesis example. why is this not dominant form of photosynthesis?
Evolved once by purple bacteria
Consume hydrogen sulphide and produce sulphur as a waste product
Not the dominant form as there is much less hydrogen sulphide than water
dichotomy definition
2 daughter lineage
polytomy definition
Many splits (rare/don’t have enough information)
