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BIOL 1202- Final Exam Guide - Comprehensive Notes for the exam ( 92 pages long!)


Department
Biological Sciences
Course Code
BIOL 1202
Professor
S.Pomarico
Study Guide
Final

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LSU
BIOL 1202
FINAL EXAM
STUDY GUIDE

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1
CHAPTER 25
THE HISTORY OF LIFE ON EARTH
A time line for planet earth
The earth is very old, about 4.6 billion years old. As earth cooled, the oceans formed
How did life originate? Was it really spontaneous generation (start with nothing then life appears)?
Something from nothing.
The building blocks of macromolecules can be formed from nonliving matter if the conditions are right.
In the 1920's and 1930's two researchers (atmosphere changes over time, and they studied other
planets):
John Burdon Sanderson (J.B.S.) Haldane in England
Aleksandr I. Oparin, a Russian biochemist,
- Independently hypothesized that the atmosphere of the primitive Earth was probably very
different from today's.
- Early atmosphere had little or no oxygen, rich in hydrogen, methane, other hydrocarbons and ammonia.
Most of these can come from volcanic sources.
* Atmosphere (is different today) surface (make up conditions is different today) -> starting point for
what becomes life.
- Haldane and Oparin suggested that the organic compounds in the first organisms could have been
formed by the interaction of sunlight (UV radiation) and the heat (from volcanoes or lightning) with the
chemicals in the atmosphere of the primitive Earth. This process of chemical evolution is called prebiotic
evolution. Evolution before life existed
- The hypothesis of abiotic formation of organic molecules was tested in 1953 in the laboratory of Stanley
Miller and Harold Urey (see fig. 25.2).
- A variety of organic compounds were created. Amino acids, short proteins, sugars, fatty acids and
nucleotides. All the building blocks can arise without life.
- The building blocks accumulated and the simple molecules condensed into more complex ones.
Monomers into polymers. This might have taken place on the surface of minerals (clay) or in oily
droplets floating in the prebiotic soup. Sidney Fox showed that polypeptides (polymers of amino acids)
could be produced abiotic tally.
- The polymers can form aggregates which could maintain an internal environment different from their
surroundings and exhibit some biological process.
- A protocell is an example of one of these aggregates. A protein membrane with an internal
compartment. (closure, protein membranes as the closure on outside)
- The ability to reproduce, one giant step for life.
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- For life to persist after becoming established there must have been polymer molecules capable of
replicating, or making copies of, themselves.
- The first self-replicating polymers were probably nucleic acids.
One hypothesis is that RNA was probably the polymer which acted as the first genetic material.
Some of the evidence for RNA as the first genetic information is:
RNA molecules can self-replicate, up to 40 monomers can be connected abioticly into a polymer chain
Some RNA molecules, like ribozymes, are autocatalytic. That is, the RNA molecules can act to modify
themselves (or other RNA molecules).
Why doesn’t life arise today? (life changes environment and continues to change, its natural)
The atmosphere has more oxygen and the presence of oxygen can break or prevent the
formation of the chemical bonds which are needed for the abiotic formation of organic molecules.
(Life isn’t going to merge the way we think it is b/c too much oxygen around for this to happen)
The atmosphere also has developed an ozone layer (protective layer for planet) which blocks UV
radiation that may have been an energy source for the abiotic formation of organic molecules.
(chemical reactions might not have occurred without the UV which is the source of energy for
driving reactions in a certain way)
The first life forms
According to fossil evidence, the first life forms (prokaryotes) showed up around 3.5 billion years ago. Ex)
stromatolites (build rocks where they live to incorporate minerals what we lead to fossil evidence) and
fossilized stromatolite
* How do we know the age of the fossils? We used radiometric dating (see fig 25.5) (rock layer gets
created as stomatolites have isotopic abundance, some isotopes will break down and go through a
decade and get a release of radioactive particles but the decay going from what we started with to the
new isotope created occurs at a fixed rate. Fixed rate allows us to use a yard stick called half life. Amount
of time it takes to turn into daughter isotope and half remains original (gone). Daughter isotope doesn’t
change but parent (isotope) original continues to decay if its half life)
Since there was little or no oxygen, these early life forms were anaerobic.
** Photosynthetic bacteria added oxygen to the atmosphere. (For a source of oxygen, only biological
process that produces a lot of is photosynthesis. Reducing oxygen, so it goes in water and water has very
little oxygen its going to take a while before any oxygen going into water makes it into atmosphere.
Saturate water with oxygen before it going into atmosphere. Oxygen is reactive and when O2 goes in
water, stuff in water become oxidized so O2 is being used up. Presence of atmospheric Oxygen is the big
event. Production of oxygen could’ve started billion earlier. Sedimentary rocks forming and evidence in
fossil show we went from none to more. This is known as oxygen revolution. Oxygen reactions occurring
in water but once it make it into air, reactions occur on land changing the surface of the planet known as
rusted/red phase.
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