Transcript Chap. 14/17 : Origin of Life - Fort Thomas Independent Schools

Chap. 14 : Origin of Life
** Biogenesis – life coming from life as opposed
to spontaneous generation (life coming
from nonliving)
I.
Disproving Spontaneous Generation
1. Francesco Redi – flies, maggots, meat
2. Lazzaro Spallanzi – heated meat broth –
no microorganisms – killed “vital force”
3. Louis Pasteur – heated broth, curved neck of flask
- - no growth in broth. Broke off flask, growth in 1
day. Conclusion: did not kill “vital force” but rather
air contains living things that we can not see
II. Earth’s formation
- 5 billion yrs. ago – solar system together in swirling
mass of gas and dust.
- Mass collapses inward forming sun
- excess released to form planet 4.6 billion yrs. ago
- volcanic eruptions formed atmosphere which lead to
oceans
- 2.2 billion yrs. ago Earth formed as we know it today
III. Theories of Support
1.
Radioactive dating – measure the rate of decay
(breakdown) of radioactive isotopes – called half-life.
Compare C12 (stable carbon) to C14 (radioactive
carbon) in fossils. We know it takes 5,730 yrs. to be
reduced by ½. Only accurate up to about 60,000 yrs.
old.
---Can use U238 up to 4.5 billion yrs. ago.
IV. Formation of Life
1.
Alexander Oparin (1923) – said primative Earth’s
atmosphere contained : NH3, H2, H2O, CH4
a. Add high heat (volcanic eruptions) to these
chemicals and reactions occur to form simple organic
compounds (amino acids)
b. Earth cools, simple organic compounds collect in
H2O
c. Add lightning and UV radiation and these simple
compounds join to make macromolecules such as
proteins.
2. Miller and Urey (1953) – set up experiment
to test Oparin’s hypothesis.
3. Fox – proteins joined together to form
membraneous spheres called microspheres
- linking together of microspheres creates coacervates
(proteins + sugars ). Coacervates are considered nonliving because they do not contain nucleic acids but
have some ingredients of nucleic acids.
V. 1st life forms
A. Conditions on Earth – lacking O2, therefore
believed Archaebacteria were 1st cells (prokaryotes) to
appear.
Once the atmosphere began to thin, more sunlight penetrated
Earth and photosynthetic bacteria evolved. About 3 billion
years ago.
• Released O2 into atmosphere over a billion yrs. – helped
form ozone layer which was necessary for life to be
protected from UV radiation.
B. Eukaryote Cell Formation
-- endosymbiosis – evidence suggests around 2 billion
years ago a small aerobic prokaryote entered and lived
inside a larger anaerobic prokaryote. Formed a
mutualistic relationship together.
• Over time these smaller aerobic prokaryotes
evolved into mitochondria and/or chloroplast
(make energy). Evidence is that both of these
structures even today contain their own DNA
inside them (not inside nucleus) and it is
different from DNA inside the nucleus