Origin of Life_Evolution of Cells

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					The Origin of Life and the Evolution of Cells
Chapter 19

Origin of Life/Evolution of Cells
• Spontaneous Generation: Theory that states living organisms arise from non-living material.

• Biogenesis: Theory that states living organisms arise from pre-existing life.

microbes

Origin of Life/Evolution of Cells
• Redi, Francesco (Italy, 1626-1697)
– Placed meat into 4 jars.
• 2 jars were covered with gauze. • 2 jars were left uncovered. • Will covered jars end up with maggots like uncovered jars?

Origin of Life/Evolution of Cells
• Redi’s Experimental Outcome (Results):
– Uncovered Jars: Flies were first observed, followed by maggots. – Covered Jars: No maggots. – Conclusion: Biogenesis

maggot

Origin of Life/Evolution of Cells
• Needham, John (England, 1713-1781)
– Boiled mutton broth in containers sealed with cork.
• Will boiling broth kill microbes?

Origin of Life/Evolution of Cells
• Needham’s Experimental Outcome (Results):
– Within days, broth was teeming with microbes. – Conclusion: Spontaneous Generation

microbes

Origin of Life/Evolution of Cells
• Spallanzani, Abbe Lazzaro (Italy, 1729-1799)
– Boiled a meat/vegetable broth in 2 flasks.
• 1 flask was sealed. • 1 flask was left open. • Will microbes appear in both flasks?

Origin of Life/Evolution of Cells
• Spallanzani’s Experimental Outcome (Results):
– Sealed flask: no microbes – Open flask: microbes teemed – Conclusion: Biogenesis*

microbes

Origin of Life/Evolution of Cells
• * Those who believed in spontaneous generation argued that the sealed flasks excluded the “vital element”. • Vital Element: A natural force or element which sustains all living organisms.

Origin of Life/Evolution of Cells
• Louis Pasteur (France, 1822-1895)
– Placed a fermentable sugar/yeast solution into two swan-necked flasks, boiled, then broke one of the necks of the flask.
• Will microbes appear in both flasks?

Origin of Life/Evolution of Cells
• Pasteur’s Experimental Outcome (Results):
– Broken flask: microbes teemed – Unbroken flask: no microbes – Conclusion: Biogenesis
• Swan-necked flask even allowed for vital element.

Origin of Life/Evolution of Cells
• Current Thought: Life originated by either spontaneous generation or by biogenesis.
– (Which came 1st, the chicken or the egg?)

Origin of Life/Evolution of Cells
• Panspermia: Concept that life arose outside the Earth and that living things were transported to Earth and seeded the planet with life.

Earth’s Timeline

by James C. Rettie

• An alien photographer aimed a camera at earth before life began (some 750 mya). The camera was set to snap one frame a year until modern times. • Projected at the normal speed of 24 frames per second, the resulting movie playing 24 hours a day, seven days a week would take a year to view.
– Each day would span 2.1 million years and each month 62 million years.

Earth’s Timeline
• From January to March there are little signs of life on earth. • The first unicellular microbes emerge in early April. • Late April and May are dominated by marine invertebrates. • Late May sees the first of the vertebrate species. • By July, colorful land plants are blanketing the planet. • Late August sees amphibians making their first appearance on land.

Earth’s Timeline
• Late August sees amphibians making their first appearance on land. • By mid-September, the dinosaurs start to appear and continue through late November. • Birds first appear in early November. • On December 1, all the dinosaurs suddenly disappear. • By mid-December mammal ancestors come and go a few times. • At mid-day on New Year’s Eve, the earliest human ancestors arrive on earth.

Earth’s Timeline
• At 9:30 p.m. on New Year’s Eve, Homo sapiens migrate out of Africa. • At 11:52 p.m., the megafauna – mammoths, saber-tooth cats, etc. – become extinct. • At 11:55 p.m., recorded human history and civilization begin. • Twenty seconds before midnight, Columbus sails to the Americas. • And at four seconds before midnight, the automobile is invented.

Origin of Life/Evolution of Cells
BIG BANG Theory
– The universe began as a dense mass of energy that exploded approximately 13.7 billion years ago (bya). – Our solar system was formed 4.6 bya from a large cloud of gases consisting primarily of hydrogen (H=1) and helium (He=2).

The Big Bang Theory, part 1
• The cosmos undergoes a superfast inflation expanding from the size of an atom to that of a grapefruit in a fraction of a second. (10-43 sec.) • Post inflation, the universe is a seething hot soup of electrons and other particles. (10-32 sec., 1027 °C)

The Big Bang Theory, part 2
• A rapidly cooling universe allows protons and neutrons to form. (10-6 sec., 1013 °C) • Still too hot to form atoms, electrons and protons prevent light from shining: the universe is a superhot fog. (3 min., 108 °C)

The Big Bang Theory, part 3
• Electrons combine with protons and neutrons to form atoms, mostly H and He; light can finally shine. (300,000 yrs., 10,000 °C) • Gravity makes H and He gas coalesce to form the giant clouds that will become galaxies; smaller clumps of gas collapse to form the first stars. (1,000,000,000 yrs., -200 °C)

The Big Bang Theory, part 4
• As galaxies cluster together under gravity, the first stars die and spew heavy elements into space; these will eventually form into new stars and planets. (15,000,000,000 yrs., -270 °C)

Primitive Earth
• Earth formed approximately 3.9 bya. • Earth was a very different planet then:
– Volcanic activity was common. – No surface water or atmosphere existed (too hot). – Gases on earth included:
• Water vapor • Nitrogen • Carbon dioxide

Primitive Earth and the Moon

Primitive Earth
• In short, primitive earth was incapable of supporting life:
– Too hot. – No atmosphere. – No surface water.

Not-So Primitive Earth
• As Earth cooled, gases collected in the atmosphere, but still no free oxygen.
– Gases on Earth now included:
• • • • Methane Ammonia Hydrogen And still, water vapor & carbon dioxide.

Not-So Primitive Earth
• Further cooling condensed water vapor into rain which collected in depressions in the earth’s surface.

Not-So Primitive Earth
• Energy on earth included radiation from UV rays, lightning, & volcanic heat.

UV Rays
Lightning

Volcanic Heat

Formation of Organic Molecules
• A primordial soup rich in organic molecules was formed on earth’s surface – a process which took over 500 million years. • From these organic molecules, macromolecules could be formed.

Formation of Organic Molecules
• Atmospheric molecules activated by energy synthesized organic molecules. • The absence of atmospheric O allowed organic molecules to exist – otherwise broken down. • The absence of heterotrophs allowed organic molecules to exist – otherwise eaten. • Organic molecules that formed in the atmosphere were washed to earth’s surface by rain.

Formation of Organic Molecules
• Dehydration Synthesis
– Evaporation of H2O combined & concentrated macromolecules.

– Freezing of H2O combined & concentrated macromolecules.

Modern Earth
• Oxidizing Atmosphere
– An oxidizing atmosphere (with O2) began to develop 2 bya. – Prokaryotes (cyanobacteria), capable of photosynthesis, started to fill the atmosphere with O2. – Ozone (O3) began to collect in the upper atmosphere shielding the earth from UV radiation.

Modern Earth
• Oxidizing Atmosphere
– Without UV Radiation - spontaneous formations of organic molecules decreased along with mutations. – Without New Organic Molecules Forming life began to proliferate through spontaneous mutations and evolution. – With Oxygen - aerobic cellular respiration began to occur.

Origin of Life/Evolution of Cells
• Formation of Organic Molecules
– Began about 4 bya and lasted for the next 1.5 billion years. – The earliest fossils of cells date back 3.5 bya.

Geological Processes vs. Ancient Bacteria (?)

Evolution of Cells
• Prebionts: Non-living structures that could potentially form living cells.
– Composed of carbohydrates, lipids, proteins, and nucleic acids.

Prebionts

Evolution of Cells
• Coacervates: Collection of organic macromolecules surrounded by water molecules forming a sphere.

Coacervates

Evolution of Cells
• Coacervates exhibit “life-like” characteristics though technically not living :
• • • • Absorb and incorporate chemicals into structure. Structure possesses a specific design. Enzymatic reactions occur. Under favorable conditions, grow and divide.

• No type of membrane is present.

Coacervates

Evolution of Cells
• Microsphere: Collection of organic molecules with a double-layered outer boundary composed of proteins.

Microspheres

Evolution of Cells
• Microspheres exhibit “life-like” characteristics though technically not living :
• Osmosis occurs across outer boundary. • With ATP, builds proteins and nucleic acids. • Reproduction occurs by budding. • No lipids are present in the outer boundary.

Microspheres

Evolution of Cells
• Autotrophs: Organisms which utilize sunlight and simple inorganic molecules to produce organic molecules. • Heterotrophs: Organisms which capture organic molecules to generate energy.

Autotrophic Prokaryote Pseudomonas

Heterotrophic Prokaryote Nitrobacter

Evolution of Cells
• The Origin of Genetic Material - which came 1st, DNA or RNA?
– RNA is simpler than DNA, but is RNA capable of making copies of itself and storing and accessing genetic info? – DNA is more complex allowing life to make a record of itself and is subject to change in order to proliferate.

– Evolution drives from simple to complex – not the other way around.

Origin of Eukaryotic Cells
• Prokaryotes: Cells without a nucleus containing few simple organelles.
– Examples: bacteria, archaea

• Eukaryotes: Cells with a nucleus containing many complex organelles.
– Examples: plant and animal cells

Prokaryotic Cells

Eukaryotic Cells

The Endosymbiotic Theory
• The Endosymbiotic Theory
– Certain organelles found in eukaryotic cells may have originated as free-living prokaryotes that were incorporated by larger prokaryotes through ingestion without digestion.
• Examples: Mitochondria & Chloroplasts

The Endosymbiotic Theory


				
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