arimasukedo

Evolution (part 1)

In Uncategorized on April 13, 2011 at 12:17 am

Describe four processes needed in order to start life on earth:

1. Organic molecules are required. Obviously, early earth did not have any of these.

2. Polymers. Without polymers such as polypeptides formed from the connecting of monomers, more complex organic compounds such as proteins cannot be built.

3. The ability to replicate (have self-replicating molecules)

4. A means to avoid molecules being polymerized by water.

What did Miller and Urey do in order to create their experiment? What was the result?

Miller and Urey recreated the environment of the Earth as they believed it would have been during the Hadean (Eon). They did this by:

  1. introducing gases that they believed were present on earth at the time (e.g. ammonia, methane, hydrogen)
  2. keeping everything at a warm temperature
  3. heating water (so that it would evaporate) and cooling water (so that it would condense) in order to recreate the water cycle
  4. generating electric sparks in order to represent lightning.

The result of this experiment was that they found organic compounds such as amino acids, certain sugars, and nucleic acids  had formed.

Why might comets have brought life to earth?

Organic molecules hitchhiking on comets could have survived an impact on the Earth’s surface. Furthermore, the strength of the impact could help to polymerize certain amino acids into polypeptides.

What are some possible locations where conditions would allow the synthesis of organic molecules?

Space
Spectral lines of cosmic duct particles reveal the presence of glycine, which is one of the simplest amino acids. (This suggests that organic molecules could form in space, and it could explain why comets could be carrying such molecules)

Laboratory experiments which recreate the environment of space have been able to synthesize amino acids. (Supports the hypothesis that organic molecules could have originated in space, brought to earth by comets or meteorites)

Alternating Wet-Dry Conditions (think the seashore, or the flood plains of a river)

The drying of clay molecules could catalyze reactions and form early organic molecules.
Stromatolites are one of the most ancient forms of life, and they are found in such areas. (This suggests that such conditions were favourable to early life on Earth)

Near Volcanoes

Volcanoes spew out water vapour, other gases, and minerals that could be used to form organic matter. The rich sources of raw materials and warmth could have provided favourable conditions.

Deep oceans

Hydrothermal vents. Hot water rises and picks up countless minerals along the way. Entire communities living around these vents (e.g. tube worms which absorb minerals from water and transfer them to symbiotic bacteria who make food from it) disproving the idea that the bottom of the ocean is lifeless due to its lack of sunlight.

Other difficulties for early life

No protective ozone layer (UV radiation 100 times above today’s levels)

What are two properties of RNA that would have allowed it to play a role in the origin of life?

RNA doesn’t require enzymes in order to replicate itself (The prebiotic world did not have enzymes)
RNA can act like a catalyst to help certain chemical reactions the way enzymes do.

What are protobionts?
Protobionts are systems considered to be the pre-cursors to prokaryotic cells.

Proteinoid Microspheres: Polypeptide chains formed when clay dries out and is then heated. In the right conditions, these chains will form proteinoid microspheres, which are tiny bubble-like structures, capable of establishing and maintaining a chemistry within its interior that is different from its surroundings.

Coacervate: Another type of microscopic sphere, these form from lipids in water. They form spontaneously due to hydrophobic forces between water and lipid molecules. Also capable of establishing and maintaining and chemistry different from exterior. Is selectively permeable.

What is the significance of protobionts?

They are capable of protecting polymers from their destructive environment. This thus makes them good candidates for primitive versions of what would become the first cell membranes. If polynucleotides like RNA are placed within these microscopic spheres, they will be protected from breaking down. Over time, true cell membranes and other cell characteristics might develop.

What role did prokaryotes play in the creation of a oxygen rich atmosphere?

Early forms of life were anaerobic cells. These anaerobic cells consumed organic molecules like simple sugars that were forming on earth as a result of chemical reactions that were occurring. They continued to reproduce, and eventually, this led to a food shortage.

However, some prokaryotes had the ability to produce food. This capacity to photosynthesize first developed at around 3.5 billion years ago. Thus, these prokaryotes had an advantage when this food shortage occurred.

Development of photosynthesis also meant mass pollution of atmosphere with oxygen. This killed off large populations of anaerobic bacteria, aside from the ones protected by mud or some other sort of barrier. Anyway, tl;dr, photosynthetic bacteria did well, and reproduced loads and continued to pollute the atmosphere with oxygen.

The endosymbiotic theory

What is the endosymbiotic theory?

It is the theory of how prokaryotes developed into eukaryotes.

But what is the endosymbiotic theory?

Organielles found inside cells today were once independent prokaryotes. Host cells that engulfed them didn’t have enzymes, so they were kept alive in exchange for their services, rather than being digested. By natural selection, the cells with photosynthetic prokaryotes/ones that were able to metabolize food/etc. were more likely to survive.

What is backing this theory?

Mitochondria and Chloroplasts both have these characteristics which make them more like independent prokaryotes and less like organelles.

  1. The double membrane
  2. The circular naked DNA
  3. Ability to perform protein synthesis using small ribosomes
  4. Can make copies of themselves

What are some criticisms of the endosymbiotic theory?

1. First off, the ability to engulf other cells and have them survive does not mean that the host cell can pass on the genetic code to synthesize the organelles
2. When chloroplasts and mitochondria are removed from cells, they can’t survive on their own.

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