[BSC 120] - Midterm Exam Guide - Comprehensive Notes for the exam (22 pages long!)

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BSC 120
MIDTERM EXAM
STUDY GUIDE
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Chapter 25 the history of life on earth
Timeline
o Earth forms 4.6 billion years ago
o Prokaryotes formed 3.5 billion years ago life alters geology
o Eukaryotes formed 2.1 to 1.8 billion years ago
o Multicellular eukaryotes formed 1.2 billion years ago
o Fungi, plants, and animals formed 500 million years ago
Francesco Redi (1668)
o Use of controlled experiment
o Spontaneous generation of life disproved this theory
Correlation is not causation
o Took meat and jars to show the presence or absence of maggots
Louis Pasteur (1862)
o Evidence against contemporary spontaneous generation
o Bacteria in swan neck flask
Three scenarios for the origin of life
o Different ideas that are testable through experimental simulations
o Scenario 1
According to one hypothesis, the first organisms were products of
chemical evolution in 4 stages
Stage 1: abiotic synthesis of organic monomers
Most extensive studied by scientists in the laboratory
Vitalism: organic molecules once thought to be produced only by
living organisms
o BUT, in 1828 Fredrich Wohler synthesized urea 
(from lead cyanate and ammonia)
A.I. Oparin and J.B.S. Haldane
o Hypothesized that early earth atmosphere was reducing
lots of free electrons
o Energy: UV radiation and lighting
o Observation: modern biological macromolecules are all
composed of elements that were present in abundance on
the early earth
o Question: can biological molecules form spontaneously
and accumulate under conditions like those on the early
earth?
So how can one test the oparin-haldane hypothesis?
o Simulation of the conditions of early earth will allow the
formation of biological compounds
“tal iller ad Harold Ure’s  eperiet uiersit of
Chicago
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o Hypothesis: a closed system designed in the laboratory to
simulate early earth conditions that produce biologically
important organic molecules from inorganic ingredients
o Prediction: organic molecules would form and accumulate
o Experiment: an apparatus was built to mimic the early
earth atmosphere and included: Hydrogen gas, Methane,
Ammonia, and Water vapor. Sparks discharged into the
chamber to mimic the prevalent lightning of the early
earth. A condenser to cool the atmosphere, causing water
ad dissoled opouds to rai ito the iiature
sea
o Results: after the apparatus had run for a week, an
abundance of organic molecules essential for life had
olleted i the sea, iludig aio aids, the
monomers of proteins
o Since miller and Ure’s experiments, laboratory analogues
of the primeval earth have produced
All 20 amino acids
Several sugars
Purines and pyrimidine bases
Lipids
ATP (when phosphate is added)
Stage 2: abiotic synthesis of polymers (proteins and nucleic acids)
Researchers have brought about the polymerization of monomers
to form polymers, such as proteins and nucleic acids, by dripping
solutions of organic monomers (amino acids or RNA nucleotides
onto hot sand, clay, and rock
As molecules absorb to the clay mineral particles they become
concentrated (stick to the surface particles)
These clay particles (coacervates) may have been essential
catalysts in the formation of polymers
Polynucleotides have tendency to copy themselves using
complementary base pairing
This was probably catalyzed by the presence of clay particles and
metal ions
Single-stranded polynucleotides = RNA
Stage 3: formation of protocells (= membrane-bounded sacs containing
genetic material and metabolically-active molecules)
A key step in the origin of life was the isolation of a collection of
abiotically created molecules within a membrane
Laboratory experiments demonstrate that protocells could have
formed spontaneously from abiotically produced organic
compounds
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