Genes Evo & Dev L3 Flashcards
Describe theories of how Life began on Earth?
Earth vs. Geothermal vents
- Earth -> 4 billion yrs -> Heredian -> “Darwin’s warm muddy pond theory”
- ->Repeated destruction -> Brings water.
- ->Strong sun -> high UV radiation at surface of water. -> no life above.
- Deep Sea -> 3.8 billion years
- ->Proton gradients surrounding alkaline hydrothermal vents Eg. “Lost City” in mid-Atlantic -> possibly supplied energy to fuel first replication.
Evidence supporting theory life started with Hydrothermal vents?
- Harbour geological manifestations of both kinds of energy used by life -> chemically reactive compounds & natural proton gradients.
- Remain active for up to 100,000 yrs -> provide constant source of energy over long geological timescales.
- Proton gradients at Lost City -> same magnitude & orientation as those in modern auto-trophic cells.
First replicating molecules?
RNA
How did proteins & DNA evolve from RNA in the RNA world hypothesis?
Basis for both reproduction & biochemical interaction -> acting as enzymes.
–> Possible combination of Amino acids -> found on comets -> by RNA -> creates proteins. Re-placed RNA enzymes -> wide range of biological functions eg. structural, enzymes, etc. ad-vantageous.
–> DNA evolved & replaced RNA.
- Double helix -> more stable for storage of info & identification of errors
- More resistant to effects of sunlight & cell membrane additional protection.
- Faster chemical reactions & DNA replication using protein enzymes.
- Formed LUCA
What is thought to have existed first, life or cells? Support your answer & mention two examples of where this may be found.
•Likely that cells existed before life itself.
–> RNA extremely reactive / unstable -> needs protection/barrier.
–>In order for chemical reactions to occur & creation of energy -> life; tiny molecules have to react/combine. -> Miniscule therefore requiring contained environment for reaction to occur as molecules otherwise may not have met.
- Tiny pores in rocks around hydrothermal vents
- Also hypothesised -> lipid protobionts reproduced & metabolised.
What conditions were required on earth for LUCA/life?
Requires cool temperatures, gravity, water & protection from radiation
Outline evolution of first prokaryotes
- -> Cyanobacteria -> produced O2
- -> Methanogeneic bacteria consumed this O2 for hundreds of millions of years.
- -> Methanogens extinct -> possibly changes in trace metals in sea.
Describe how eukaryogenesis may have occurred.
Evolution of eukaryotes -> 2 billion years ago.
Eukaryotes can be single-celled ; but to be multicellular -> must be eukaryote.
Likely caused by heterotrophic eubacterium being engulfed by archaebacterium.
This eventually became mitochondria.
Mitochondria enable large complex life due to energy they provide.
Bacterium engulfed by eukaryotic plant ancestor.
Examples of Ediacaran biota
- Spriggina -> Annelid worm/arthropod? – 3cm long
- Dikinsonia -> Up to 1m in length
- Rangeomorphs -> Fractally branched, fern-like. -> Dark depths of ocean. -> Ecology suggests they were animals.
- Erniettmorphs -> modular or quilted.
Evidence of the Cambrian explosion?
The Cambrian Explosion -> 515-540 million years ago -> Burgess Shale.
Most types of common animal today appeared over 20-30 million years. Eg. Arthropods, chordates, worms.
Soft bodies preserved in Burgess Shale (Canada), China, Greenland & Russia
Some can’t be categorised into modern taxonomy Eg. Opabinia -> 7cm long.
How/why did the Cambrian explosion occur?
- Physiological change -> dissolved O2 levels enabled active lifestyle
- Geographical change -> Formation of new seas -> new niches
- Geochemical change -> Changing Sea levels led to abundance of trace metals -> used to make exoskeletons.
- Biological change -> Incr. zooplankton enabled enabled evolution of new predators -> further incr. selection pressures.
- Other geological & biological factors -> Eruptions caused by comet impacts weakened species
Dinosaurs & large reptiles died
Ecological niches of extinct species (pterosaurs, mesosaurs) -> left space for evolution of birds & mammals.
(–NB. -> Mammals present for majority of Jurrasic era.)
-> Recovery of ecosystem from mass extinction -> 20 million years.
How were eukaryotes able to evolve as a result of Cambrian explosion?
- Other geological & biological factors -> Eruptions caused by comet impacts weakened species
Dinosaurs & large reptiles died
Ecological niches of extinct species (pterosaurs, mesosaurs) -> left space for evolution of birds & mammals.
(–NB. -> Mammals present for majority of Jurrasic era.)
-> Recovery of ecosystem from mass extinction -> 20 million years.
Describe the Permian mass extinction, what caused it & the resulting factors.
• End of Permian -> mass extinction. (250 million years ago)
- 95% sea-life extinct -> All trilobites & placoderms (armoured fish) , 99% plankton genera.
- 70% all families of land animal extinct
- Multiple factors Eg. Volcanism, tectonic plates, asteroids may have caused rapid widespread climate change.
- Diapsids (early dinosaurs) & cartilaginous fishes populations able to grow.
- Theraspids (our ancestors) just survived.
Outline evolution of the eye
• Evolution of the eye: (50-100 times)
1. Light-sensitive cells/photoreceptors/pigment built onto membrane -> single celled organisms.
Enabled them to swim toward light.
2. Cup-shaped hollows
Enabled to sense direction of light.
3. Pinhole iris
Incr. resolution -> sharper image.
Narrows to become sharper -> this decreases available light & decr. sensitivity.
4. Protective crystalline covering over iris.
Focus & control of light entering eye.
Lens to focus light.
Why was evolution of the lens successful?
Protein opsins -> molecular basis for all sight
First functioned as clocks more than light sensors -> combined with melatonin which dies upon contact with light -> enabling detection of daybreak by absence of melatonin.
Continually generate melatonin for next day of use but chromophores could just change shape continuously.
