Study Questions - Origin of Life
Readings - Lane
1. What major energetic shortcoming does Lane see with the 'genetic system first' model?
2. What chemical and physical characteristics of white smokers led Lane to hypothesize that life originated there?
3. All life uses a proton gradient as an energy source. How does Lane explain the formation of a natural proton gradient in white smokers 4 bya, and how did the differences in ocean chemistry (from modern ocean chemistry) factor in?
4. Why would an initial protomembrane need to be leaky to maintain the proton gradient? Why couldn't a pump evolve with a leaky membrane?
So, in order for protocells to leave the vent and colonize the planet (as they evidently did), they need to evolve the ability to create a proton gradient themselves - that is no longer dependent on the unique conditions of the vent. This means evolving a membrane impermeable to H+ ions (soa gradient will be maintained), and an ion pump (to establish the gradient). This isn't a question... !!
5. What is an 'anti-porter'?
6. What is the adaptive benefit of an antiporter through which Na+ are expelled when H+ ions flow into the cell in response to the natural concentration gradient of the vent? Why can a Na+ gradient be established but not a H+ gradient?
7. This next step is the tricky one. Why is it adaptive NOW, with the anti-porter in place, to evolve a H+ pump - even though the membrane is leaky to H+?
8. Why would a Na+ pump work just as well at expelling H+ ?
9. Now, with a H+ pump, why is an impermeable membrane adaptive?
10. Now, with an impermeable membrane and a proton pump, what can the protocell do?
11. How might the late divergence of protocells at the membrane forming stage account for the similarities and differences in archaea and bacteria in DNA and membranes, respectively?
12. Lane suggests there are energetic reasons why eukaryotes are the only domain to evovle multicellularity and structural complexity (built with proteins). Describe his hypothesis by relating these ideas: energy/gene relationships, genome reduction in the endosymbiont, and energetic capacity of the host.
13. The 'split-gene' structure of eukaryotic genomes traces back to the origin of eukaryotes. Old genes have introns in the same places across all eukaryotes. What functional relationship is there between mobile type II introns in bacteria and the RNA in splicesomes?
14. How might the need to splice out invading introns have selected for the presence of a nuclear membrane?
15. How might the increasingly large eukaryotic genome (gathering genes from the endosymbionts), peppered with invading introns that cause mutations, have selected for recombination and sex?