Crossing the Chasm from Prokaryotic to Eukaryotic Cells Flashcards
Describe the symbiogenesis theory with regards to the mitochondria
eukaryotic cells are prokaryotic chimeras, after the stable incorporation of a free living but symbiotic alphaproteobacteria by an ancestral archaeon approximtaley 2000Mya
Describe the symbiogenesis theory with regards to the chloroplasts
the symbiont is hypothesised to be an ancient cyanobacterium, approximately 1800Mya
Describe the basics of the sulphur syntrophic theory
- archaeon was a sulfur-reducing entity
- alphapoteobacterium was sulfur oxidising
Describe the specifics of the sulphur syntrophic theory
- archaeon would take up organic nutrients, transforming them into hydrogen sulfide and carbon dioxide
- export to the symbiont
- bacterial symbiont would take up these products and oxidise the hydrogen sulfide, producing sulfurous compounds and organic nutrients
- transfer back to the host
Describe the basics of the hydrogen hypothesis
- archaeon was anaerobic and hydrogen consuming
- facultatively anaerobic bacteria hydrogen producing
Describe the role of the archaeon in the hydrogen hypothesis pre-symbiogenesis
archaeon takes up hydrogen and carbon dioxide from a shared geological source, producing glucose and ATP through the acetyl CoA and autotrophy pathways, and producing methane and ATP via methanogenesis
Describe the role of the bacteria in the hydrogen hypothesis pre-symbiogenesis
- bacteria use anaerobic metabolism to take up carbon from an organic source, producing glucose and ATP which would then be used in their fermentation pathways, producing pyruvate as well as hydrogen, carbon dioxide and Ac- and releasing these products to the ambient environment. – as aerobic metabolism, they would take up oxygen, producing ATP, carbon dioxide and water though oxidative phosphorylation.
Describe a facultatively anaerobic bacteria
bacteria capable of using either fermentation or aerobic respiration as a metabolic mechanism
Describe the symbiogenesis event under the hydrogen hypothesis
- occur post-inactivation of the geological source
- hydrogen and carbon dioxide products from the bacteria would be taken up by the archaeon, in order to maintain autotrophy and methanogenesis
- two bacteria would be engulfed
Describe the consequences of bacterial engulfment under the hydrogen hypothesis
transfer the entity from one where organic compounds were taken up by the bacterium, hydrogen, carbon dioxide and Ac- were transported to the archaeon, and methane out into the system, into one where the organic compounds were taken up by the archaeon, and the hydrogen, carbon dioxide and Ac- were also emitted by the archaeon, via the bacteria
Describe the location of the hydrogen hypothesis
alkaline deep-sea hydrothermal vents
Describe the tenets of the hydrogen hypothesis
- transfer of genes from the engulfed bacteria to the host archaeon via unicellular bacterial rupture
- double engulfment
Describe the specific genetic tenets of the hydrogen hypothesis
- gene for the bacterial glucose transporter would have to be incorporated into and expressed by the host genome immediately downstream of a native promotor without a frameshift mutation
- into a functional protein that would be targeted to the archaean cell membrane.
Explain the retention of the oxidative phosphorylation pathway by the bacterial endosymbiont
- latter migration from the benthic to the upper zones, with a higher concentration of oxygen therefore increasing the efficiency of aerobic metabolism
- extra energetic provision of mitochondria
Describe the environment of the deep-sea hydrothermal vents
- hydrothermal spring water between the crust: 100 degrees Celsius
- contains hydrogen sulphide and hydrogen, which invade the above mounds
- belch out nickel and iron compounds and carbon dioxide
Describe hydrothermal mounds
- clay, silica and carbonate precipitates
- pervade through the crust
- attached to the ocean floor
- surrounded by ocean water of less than 20 degrees Celsius
The limiting factor of bacterial survival is
in the speed of replication
Describe the effects of replication speed limiting bacterial survival
- quiescence under starvation
- on nutrient provision, exponential mutiplation until source exhaustion
What is the selectable trait in bacteria?
- food exploitation
- replication rapidity
Why do bacteria exhibit small genomes?
Since DNA replication is the rate limtiing step of cell multiplication, it is positively selected for for a bacteria to exhibit a small genome.
Describe eukaryotic life history strategies
underpinned by slow replication, but large genomes which facilitate a greater proteinaceous diversity, and therefore resilience to various environments through compettive advantages and pathogenic defence.
The evolution of larger genomes was
key to the success of eukaryotic cells
Describe the advantages of a large genome
- larger arsenal of protein weapons to beat competition
- more complex pathogen defences
- more complex signalling and regulatory systems that allowed multicellularity
- cell-type specific isoforms of proteins, allowing cell-specialisation in multicellular organisms
Eukaryote genomes are typically … of times bigger than bacterial genomes and encode … times as many proteins
thousands, approximately 10
What are the effects of having a larger genome and protein complement?
requires dramatically more energy per cell to synthesise and maintain
How are energetic requirements of eukaryotes met?
mitochondrial acquisition
Describe the mitochondrial genome
less than 40 genes
Explain the effects of having the oxphos genes in the mitochondrial, rather than plasma- membrane
- cell and genome size not limited due to a greater surface area: vol
- greater ATP generation possible
How is the mitochondrial genome so small?
Transfer of genetic information to host
What is the effect of having a small mitochondrial genome?
local replication of the reduced genome is less energetically costly, relative to both the pre-gene transfer state, and to bacteria, who must replicate their entire genome.
Eukaryotes have a … cost per genome
low
Compare the energy available per expressed gene in eukaryotes versus bacteria
- 57.15 to 0.03 femtoWatts per gene
- nearly 2000 fold greater
