Lecture 2b Flashcards
Describe the four stages of the hypothesis for the origin of life on earth by chemical evolution
1) abiotic synthesis of small organic molecules
2) The joining of these small organic molecules into macro-molecules
3) Packing of these molecules into Protobionts
4) Origin of self-replicating molecules that made inheritance possible
Supporting evidence of stage 1 (abiotic synthesis of organic molecules)
Oparin and Haldane hypothesized that conditions of early earth favored the formation of organic molecules from inorganic precursors
- Could not happen today b/c of O2 levels (attacks chemical bonds).
- Energy provided by intense UV radiation (no ozone) and lightening.
- Slow accumulation of organic molecules in early oceans —> “prebiotic soup”.
Miller and Urey tested Opran and Haldanes’ hypothesis and were able to produce a variety of amino acids and oganic molecules
Supporting Evidence of stage 2 (The joining of these small organic molecules into macro-molecules)
- Could macromolecules such as proteins and nucleic acids have formed on early Earth?
- By dripping solutions of amino acids onto hot sand, clay, and rock, researchers have been able to produce amino acid polymers, without the help of enzymes.
Supporting evidence of stage 3 (packing of these molecules into protobionts)
Protobiont: First non-living structure collections of
abiotically produced molecules and macromolecules surrounded by a membrane or membrane-like barrier.
Able to maintain internal conditions that differ from surroundings
Lab experiments proven that protobionts could have formed spontaneously from organic molecules
• Vesicles form spontaneously when lipids added to water.
• Vesicles can grow and divide on their own; membrane selectively permeable; can perform
simple metabolic reactions.
–>Constraining organic molecules within a vesicle-like structure –> increase concentration of specific
molecules —> increase probability of certain metabolic reactions occurring.
Supporting evidence of stage 4 (origin of self replicating molecules that made inheritance possible)
• First genetic material was likely RNA, not DNA.
• 3 key functions of RNA:
• Ability to store information
• Capacity for self-replication
• Can act as a catalyst (ribozymes)
• Ribozymes can:
1. Act as enzymes to synthesize macromolecules found in living cells.
2. Manufacture short, complementary copies of RNA.
• RNA is also single stranded and can assume a variety of 3D shapes.
• In a particular environment, RNA molecules with certain base structures are more stable and replicate faster, with fewer errors.
• RNA molecule best suited for the environment would therefore leave more descendent molecules.
• Lead to “RNA world” – RNA molecules carried genetic info, and replicated and stored that info in the protobionts that carried them.
Briefly describe why the proliferation of protobionts with self-replicating RNA would have been favored over those that didnt contain self-replicating catalytic RNA?
A protobiont with self-replicating, catalytic RNA could pass genetic information to offspring.
• Most successful protobionts (e.g., most selective and efficient membranes) would increase in number – can exploit resources better AND pass these abilities onto offspring!
Define Fossil
A piece of physical evidence from an organism that lived in the past fossils can take many forms including bones, shells, leaves, pollen, seeds, impressions of cells, tracks and burrows and even dung
Define Fossil Record
The total collection of fossils that have been found throughout the world
Briefly explain how fossils form
• Most processes that form fossils begin when an organism is buried in ash, sand, mud, or some other type of sediment.
• Once burial occurs, several things can happen:
1. Decomposition does not occur the organic remains can be preserved intact.
2. Sediments accumulate on top of the material compress the organic material into a film or compression fossil.
3. Remains decompose after they are buried the hole that remains can fill with minerals a cast of the remains.
4. Remains rot slowly dissolved minerals can gradually infiltrate the interior of the cells and harden into stone permineralized fossil.
• After many centuries have passed, fossils can be exposed at the surface through erosion, a road cut, quarrying, and other processes.
Explain why fossils found in sedimentary rock can be assigned a relative age
Order of fossils within rock strata =
sequence in which the fossils were laid
down –>relative ages (but not ACTUAL
age).
Differentiate between relative dating and radiometric dating
Relative dating: (comparing fossils to eachother) order of fossils within rock strata= sequence in which the fossils were layed down—-> relative age not actual age
Radiometric dating ( to determine the actual age of fossils ) based on the decay rate of isotopes Each radioactive isotope has a specific half-life that is not affected by environmental variables. • Rocks can be dated by measuring the relative amounts of radioactive isotopes and their decay products.
Explain how radiometric dating can determine actual age of rock in strata
Each radioactive isotope has a specific half-life that is not affected by environmental variables.
• Rocks can be dated by measuring the relative amounts of radioactive isotopes and their decay products.
Explain why the fossil records provides an incomplete history of life on earth
• Many organisms do not die in the right place at the right time to be preserved as fossils.
• Of the fossils that form, many are destroyed by geological processes, and only a fraction are actually discovered.
- Fossil record favors organisms that lived a long time, and were abundant and
wide-spread = Abundance bias.
- Organisms that live in areas where sediments are actively being deposited are more likely to form fossils = Habitat bias
- Slow decay is essential to fossilization; organisms with hard parts such as bones and shells tend to leave fossil evidence = Taxonomic and tissue bias
• Recent fossils are much more common in the fossil record than ancient
fossils = Temporal bias
–> Fossil record is a NON-RANDOM sample of the past!
State what the earliest evidence of life on earth is
The earliest direct evidence of life: 3.5 billion year-old fossils = stromatolites.
• Stromatolites: rock-like structures composed of layers of certain types of prokaryotes (e.g., cyanobacteria) and sediment.
Describe first single celled organisms and how they contributed to life on earth
These prokaryotes helped to shape life on
our planet – most notably by transforming
the atmosphere via the production of
oxygen.
Describe the accumulation of atmospheric oxygen over time, its source and the effect of this accumulation over time
• As the supply of organic molecules —> any cells
that had evolved the ability to make their own
organic molecules from inorganic sources would
have a growth advantage!
• Evidence suggests that photosynthesis began
early in Earth’s history.
• Earliest forms of photosynthesis were
anoxygenic (did not produce oxygen; did not
use H2O as electron donor)
• Oxygenic forms arose significantly later
• Evolution of oxygenic photosynthesis (cyanobacteria) ~ 2.7 – 2.5 b.y.a.
• Free oxygen produced dissolved in water and reacted with dissolved iron
–>formed iron oxide precipitate (seen as red layers in sedimentary rocks).
• Dissolved oxygen continued to and eventually began to “gas out” of water and enter the atmosphere (seen as rusting of iron rich terrestrial rocks).
• Oxygen levels in atmosphere increased gradually from 2.7 to 2.2 b.y.a., then shot up rapidly…why?
• Huge impact on life!
• Oxygen can be damaging to cells several prokaryotic species were doomed!
• Other species survived in anaerobic environments.
• Diverse adaptations to changing environment evolved
–> Aerobic cellular respiration!!
