Transcript 25.1-0 - Laurel County Schools

Fig. 25-1
25 History of Life on Earth
WHAT IS THE EVIDENCE?
WHAT ARE THE HYPOTHESES?
500 mya this relative of T. rex roamed Antarctica.
Today the largest fully terrestrial animal found
there is a 5 mm long fly!
MACROEVOLUTION
• Broad pattern of evolution over time
– Origin of groups of animals or plants
– Origin of photosynthesis
– Impact of mass extinctions on diversity of life
• Microevolution is the change in allele (gene)
frequency in a population
A TIMELINE
• ~13.8 Billion Years Ago – Origin Of The Universe
• ~ 4.6 BYA – Formation of the Solar System/Earth
• ~ 3.5 BYA – Evidence of Life (Prokaryotes)
• ~ 2.7 BYA – Photosynthesis – cyanobacteria –
oxygen begins to accumulate in atmosphere
• ~ 2 BYA – Eukaryotic Cells
• ~ 1.5 BYA – Multicellular Organisms
• ~ 500 Million Years Ago – Colonization of Land
• ~200,000 Years Ago – Modern Humans
25.1: Conditions on early Earth made origin of life
possible
• Chemical/physical processes on early Earth
and natural selection may have produced very
simple cells
• 4 STAGES
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into
macromolecules
3. Packaging of molecules into protobionts
4. Origin of self-replicating molecules
STAGE 1: Abiotic Synthesis of Small Organic
Molecules
• Can we test this hypothesis?
• Oparin & Haldane 1920s
• Miller and Urey 1950s
• What are alternative ideas that are testable?
STAGE 1: Abiotic Synthesis of Small
Organic Molecules
Oparin-Haldane Hypothesis – 1920s
• Organic molecules formed in ocean
from simple molecules
• Reducing Atmosphere – electron
donating
• Oxygen free (oxygen takes electrons - oxidizing)
• Energy provided by lightning and UV radiation
• Produced coacervates – carbohydrate and
protein spheres which enclosed molecules
STAGE 1: Abiotic Synthesis of Small
Organic Molecules
Miller-Urey Experiment - 1953
• Tested Oparin and Haldane ideas
• Placed H2, CH4, NH3 in closed apparatus
• Heated water to create water vapor and to collect
chemical which formed
• Electric spark provided energy (lightning)
• Molecules produced: some amino acids,
hydrocarbons, formaldehyde CH2O, cyanide HCN
Page 59
Results published
May 1953 in
Science
*Watson and Crick
published the structure
of DNA April 1953
STAGE 1: Abiotic Synthesis of Small
Organic Molecules
Miller-Urey Experiment - 1953
• Supports Oparin and Haldane ideas
• Experiment has been repeated many
times by other scientists; many variations;
similar results
• Conclusion: Organic molecules can be produced
abiotically
• Questions: What gases were actually in the early
atmosphere? Are there other testable
explanations?
STAGE 1: Abiotic Synthesis of Small
Organic Molecules
• There is some evidence early atmosphere was
primarily N2 and CO2; neither oxidizing nor
reducing; Miller-Urey-type experiments have
produced organic compounds
• Atmosphere may have been reducing near the
mouth of volcanoes and deep-sea thermal vents
• Deep-sea vents and submerged volcanoes - rich
in iron and sulfur compounds - are also likely
candidates for the first organic compounds
• Iron and sulfur are important components of some
enzymes use in ATP production
STAGE 1: Abiotic Synthesis of Small
Organic Molecules
• Extraterrestrial origin?
• Type of meteorite called a carbonaceous chondrite
are 1-2% carbon compounds
• 4.5 billion year old meteorite from Australia had
more that 80 amino acids; some similar to those
produced in Miller-Urey experiment
• Earth Contamination? No. Amino acids were
50:50 mix of L and D isomers
• Organisms make/use L isomers
COULD ABIOTIC SYNTHESIS HAPPEN?
• YES. Miller-Urey and related evidence
• YES. Volcanoes and deep-sea vents provide ideal
environment
• ORIGIN could be EXTRATERRESTRIAL –
meteorite evidence
STAGE 2: Abiotic Synthesis of Macromolecules
• Could polymers form spontaneously without the
help of enzymes? Can we test this?
• Polypeptides and RNA have been assembled
abiotically
• Drip solutions over hot sand, clay or rock
• Provides a support which concentrates and holds
the monomer.
STAGE 3: Protobionts – Membrane-bound Structures
• Replication first? Metabolism first?
• The next stage may have been enclosing
abiotically produced molecules inside a cell-like
structure – protobionts
• Can we test this hypothesis?
• We have produced very simple cell-like structures
in the laboratory
Protobionts
• Liposomes – form when lipids and other organic
compounds are added to water
– A bilayer forms – do you know why?
– They reproduce, swell and shrink in response
to the concentration of solutions they are place
in, perform simple metabolic reactions
Fig. 25-3
20 µm
Glucose-phosphate
Glucose-phosphate
Phosphatase
Starch
Phosphate
(a) Simple reproduction by
liposomes
Amylase
Maltose
Maltose
(b) Simple metabolism
STAGE 4: Self-Replicating Molecules - Inheritance
• Can we test this hypothesis?
• It is likely the first genetic material was RNA –
“RNA World Hypothesis”
• Cell contain ribozymes – RNA molecules that
function as enzymes – given RNA nucleotides they
will build short complementary pieces of RNA
• RNA is single stranded – exposed bases serve as
pattern or template for forming a new strand
• RNAs have a wide variety of shapes – different
shaped molecules could carry out different
function
STAGE 4: Self-Replicating Molecules - Inheritance
• Natural selection would favor RNAs whose
sequence was more stable and could replicate
faster in existing environmental conditions
• Copy errors occur – some would produce a more
stable shape with even better self-replication
• Early protobionts with self-replicating, catalytic
RNA would have been more effective at using
resources and would have increased in number
through natural selection
STAGE 4: Self-Replicating Molecules - Inheritance
• RNA is the “Swiss Army knife” of life
• Functions as a catalyst and comes in many
shapes
STAGE 4: Self-Replicating Molecules - Inheritance
• Eventually DNA replaces RNA as the information
molecule of the cell
– DNA is a more stable molecule – double
stranded, bases are attached to each other not
exposed to the surroundings as in RNA
– DNA makes fewer errors when replicating
– RNA video on website
– http://www.laurel.kyschools.us/olc/page.aspx?i
d=13786&s=480
LOOK OUT WORLD –
HERE COMES LIFE
• We’ve got selfreplicating
molecules,
metabolism, and
a way to maintain
and environment
different for
surroundings
“It is often said that all the conditions for the first
production of a living organism are now present, which
could ever have been present.— But if (& oh what a big
if) we could conceive in some warm little pond with all
sorts of ammonia & phosphoric salts,—light, heat,
electricity etc. present, that a protein compound was
chemically formed, ready to undergo still more complex
changes, at the present day such matter would be
instantly devoured, or absorbed, which would not have
been the case before living creatures were formed.
Charles Darwin, Letter to J. D. Hooker, Feb1871]
JUST FOR FUN: American Chef Julia Child
• The National Air and Space Museum in its The
Universe gallery used to show a video of Julia
Child recreating Stanley Miller's famous
experiment, cooking up Primordial Soup.
https://massasoit.instructur
e.com/media_objects/0_4
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