Ch. 1 Cell Evolution

RNA World Hypothesis

- RNA dominated before cells arose bc store info and catalyze rxns
- life requires autocatalysis in order to make copies of itself
- 3 steps:
1. autocatalysis: family of RNA catalyzed
2. RNA family: assume separate functions
3. Protein Synthesis: family members with different functions come together and form proteins

RNA before DNA evidence

-dna cant catalyze rxns
- ribose can be formed from formaldeyde (miller-urey product)
- clipping -OH off dna takes enzymes which didnt exist

*DNA preferred over RNA bc more stable, double stranded, easy to replicate, and easier to repair

Compartmentalization

evolutionary advantageous to wrap up RNA family so they don't float away and interact more
- phospholipid bilayers form spontaneously
*micelle forms with FA tails inside
*phospholipid bilayer forms sphere

Darwin Comp between Protocells

association between genome and membrane size
- solvent: h2o -> moves via osmosis
- solute: moves via diffusion

- increase solute in protocell = h2o moving in leading to lysis
- chen & szostack found increase in intracellular solute, increase lipid integration and increase overall size of protocell

Evolutionary Timeline

- universe form 13.8 bya
- earth formed 4.6 bya
- 1st living cell 3.8 bya
*shortly after, photosynthesis evolved because of increased UV due to no ozone layer
- aerobic respiration becomes widespread; 1st euk cell 2 bya
*cellular respiration = flow of e- thru membrane pumping proteins forming H+ gradient to make ATP

Evolution of Eukaryotes

1st hypothesis:
- archaea randomly invaginate and form nuclear envelope (out + in mem) and formed the rough ER
*adv bc it provides double protection

2nd hypothesis:
- anaerobic archaean engulfed an aerobic bacterium and established permanent residence -> Endosymbiosis Hypothesis

Endosymbiosis Hypothesis

"Origin of Mitochondria" Margulis 1970s

- adv bc mother cell gets increased ATP and engulfed cell is protected

Evidence:
- cellular predators & phagocytosis of prey
- current endosymbiosis examples
- bac and mito are 2 um in size
- modern bacteria respire
- mito &chloro have own circular DNA that codes for some proteins
*once bacteria swap DNA, mito establish permanence & can't separate
- mito and chloro have double membrane
- mito and chloro apart of vesicular pathway
- mito and chloro transporters similar to bac PM transporters

Hydrothermal Origin of Life/Iron-Sulfer World Hypothesis

- deep sea hydrothermal vents (increase heat, increase pressure)
- mineral cluster = e- carriers
- carbon monoxide + e- carriers -> pyruvate
- pyruvate and amine group -> alanine = build peptide library
- pyruvate UNSTABLE in RNA world

Overview of molecules to eukaryotes

molecules -> protocell -> common ancestor -> bacteria or archaea -> eukaryotes

*either via RNA world or Fe/S world hypothesis