Crossing the Chasm from Prokaryotic to Eukaryotic Cells

Question 1

Describe the symbiogenesis theory with regards to the mitochondria

Answer 1

eukaryotic cells are prokaryotic chimeras, after the stable incorporation of a free living but symbiotic alphaproteobacteria by an ancestral archaeon approximtaley 2000Mya

Question 2

Describe the symbiogenesis theory with regards to the chloroplasts

Answer 2

the symbiont is hypothesised to be an ancient cyanobacterium, approximately 1800Mya

Question 3

Describe the basics of the sulphur syntrophic theory

Answer 3

• archaeon was a sulfur-reducing entity
• alphapoteobacterium was sulfur oxidising

Question 4

Describe the specifics of the sulphur syntrophic theory

Answer 4

• 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

Question 5

Describe the basics of the hydrogen hypothesis

Answer 5

• archaeon was anaerobic and hydrogen consuming
• facultatively anaerobic bacteria hydrogen producing

Question 6

Describe the role of the archaeon in the hydrogen hypothesis pre-symbiogenesis

Answer 6

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

Question 7

Describe the role of the bacteria in the hydrogen hypothesis pre-symbiogenesis

Answer 7

• 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.

Question 8

Describe a facultatively anaerobic bacteria

Answer 8

bacteria capable of using either fermentation or aerobic respiration as a metabolic mechanism

Question 9

Describe the symbiogenesis event under the hydrogen hypothesis

Answer 9

• 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

Question 10

Describe the consequences of bacterial engulfment under the hydrogen hypothesis

Answer 10

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

Question 11

Describe the location of the hydrogen hypothesis

Answer 11

alkaline deep-sea hydrothermal vents

Question 12

Describe the tenets of the hydrogen hypothesis

Answer 12

• transfer of genes from the engulfed bacteria to the host archaeon via unicellular bacterial rupture
• double engulfment

Question 13

Describe the specific genetic tenets of the hydrogen hypothesis

Answer 13

• 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.

Question 14

Explain the retention of the oxidative phosphorylation pathway by the bacterial endosymbiont

Answer 14

• 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

Question 15

Describe the environment of the deep-sea hydrothermal vents

Answer 15

• 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

Question 16

Describe hydrothermal mounds

Answer 16

• clay, silica and carbonate precipitates
• pervade through the crust
• attached to the ocean floor
• surrounded by ocean water of less than 20 degrees Celsius

Question 17

The limiting factor of bacterial survival is

Answer 17

in the speed of replication

Question 18

Describe the effects of replication speed limiting bacterial survival

Answer 18

• quiescence under starvation
• on nutrient provision, exponential mutiplation until source exhaustion

Question 19

What is the selectable trait in bacteria?

Answer 19

• food exploitation
• replication rapidity

Question 20

Why do bacteria exhibit small genomes?

Answer 20

Since DNA replication is the rate limtiing step of cell multiplication, it is positively selected for for a bacteria to exhibit a small genome.

Question 21

Describe eukaryotic life history strategies

Answer 21

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.

Question 22

The evolution of larger genomes was

Answer 22

key to the success of eukaryotic cells

Question 23

Describe the advantages of a large genome

Answer 23

• 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

Question 24

Eukaryote genomes are typically … of times bigger than bacterial genomes and encode … times as many proteins

Answer 24

thousands, approximately 10

Question 25

What are the effects of having a larger genome and protein complement?

Answer 25

requires dramatically more energy per cell to synthesise and maintain

Question 26

How are energetic requirements of eukaryotes met?

Answer 26

mitochondrial acquisition

Question 27

Describe the mitochondrial genome

Answer 27

less than 40 genes

Question 28

Explain the effects of having the oxphos genes in the mitochondrial, rather than plasma- membrane

Answer 28

- cell and genome size not limited due to a greater surface area: vol - greater ATP generation possible

Question 29

How is the mitochondrial genome so small?

Answer 29

Transfer of genetic information to host

Question 30

What is the effect of having a small mitochondrial genome?

Answer 30

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.

Question 31

Eukaryotes have a ... cost per genome

Answer 31

low

Question 32

Compare the energy available per expressed gene in eukaryotes versus bacteria

Answer 32

- 57.15 to 0.03 femtoWatts per gene - nearly 2000 fold greater