14.2 The Origin Of Life Watch Video:the Origins Of Life

14.2 The Origin of Life watch video:The Origins of Life (1/2) ABIOGENESIS: The Origins (2/2)

Interesting Examples… • For centuries people (including scientists) believed that simple living organisms could come into being by spontaneous generation. This was the idea that nonliving objects can give rise to living organisms. It was common “knowledge” that simple organisms like worms, beetles, frogs, and salamanders could come from dust, mud, etc., and food left out, quickly “swarmed” with life. For example:

Interesting Examples… reference http://biology.clc.uc.edu • Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times. – Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs.

Interesting Examples… reference http://biology.clc.uc.edu • In many parts of Europe, medieval farmers stored grain in barns with thatched roofs As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around. – Conclusion: It was obvious to them that the mice came from the moldy grain. –

Interesting Examples… reference http://biology.clc.uc.edu

• Observation: Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them. – Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies.

Biogenesis Experiment reference http://biology.clc.uc.edu • In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat. This was a true scientific experiment — many people say this was the first real experiment — containing the following elements:

Biogenesis Experiment reference http://biology.clc.uc.edu • • • •

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Observation: There are flies around meat carcasses at the butcher shop. Question: Where do the flies come from? Does rotting meat turn into or produce the flies? Hypothesis: Rotten meat does not turn into flies. Only flies can make more flies. Prediction: If meat cannot turn into flies, rotting meat in a sealed (fly-proof) container should not produce flies or maggots. Testing: Wide-mouth jars each containing a piece of meat were subjected to several variations of “openness” while all other variables were kept the same.

Biogenesis Experiment reference http://biology.clc.uc.edu •

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control group — These jars of meat were set out without lids so the meat would be exposed to whatever it might be in the butcher shop. experimental group(s) — One group of jars were sealed with lids, and another group of jars had gauze placed over them. replication — Several jars were included in each group. Data: Presence or absence of flies and maggots observed in each jar was recorded. In the control group of jars, flies were seen entering the jars. Later, maggots, then more flies were seen on the meat. In the gauze-covered jars, no flies were seen in the jars, but were observed around and on the gauze, and later a few maggots were seen on the meat. In the sealed jars, no maggots or flies were ever seen on the meat. Conclusion(s): Only flies can make more flies.

Early Ideas of Origin

biology.clc.uc.edu

vilenski.org

Spontaneous generation is the idea that life arises from non-life. This idea was rejected in the mid-1800's. It was replaced by the theory of biogenesis which states that only living organisms can produce other living organisms.

Theory of Biogenesis • Pasteur used a similar experiment to show that this applied to microorganism as well as organisms like flies which are visible.

Modern Ideas of Origins If life can arise only from preexisting life then how did we first appear? • Haldane and Oparin were the first to speculate on the spontaneous origin of life. The Haldane-Oparin Hypothesis proposed that the precursors of life's molecules formed from inorganic sources

Miller and Urey • Chemist Stanley Miller and physicist Harold Urey did a famous experiment in 1950 to test this theory. They mixed gases thought to be present on primitive earth: • • Methane (CH4) • Ammonia (NH3) • Water (H2O) • Hydrogen (H2)

Modern Ideas of Origins They tested the HaldaneOparin hypothesis with a device that simulated the primitive environment. Using a mixture of gases and applying an electrical discharge, they succeeded in synthesizing amino acids, Because AAs are the building blocks of proteins this supported the primordial soup hypothesis

Making Proteins • Clay would have been a common sediment in early oceans, and it could have provided a frame work for protein assembly. See figure 14.14 in our text

Modern Ideas of Origins continued ………….

• A requirement for life is the coding system for protein production (DNA or RNA). • Another important step in evolution of life was the formation of membranes. Connection between the various chemical events and the overall path from molecules to cells remains unresolved

Cellular Evolution • Scientists hypothesize that the first cells were prokaryotic cells. • Many scientists think that modern prokaryotes called archaea are the closest relatives of Earth’s first cells. • These organisms live in extreme environments, such as the hot springs of Yellowstone Park or volcanic vents in the deep sea. They do not need oxygen. Scientists believe that the earth’s earliest atmosphere did not contain oxygen.

Cyanobacteria • Photosynthesizing bacteria (cyanobacteria) probably evolved after the archaea (based on fossil record) These bacteria would have released oxygen

Cyanobacteria • The oxygen would have produced an ozone (protective) layer around the earth which would have set the conditions for the first eukaryotic cell

The Endosymbiont Theory • This theory was proposed by Lynn Margulis in 1966. It is hypothesized that eukaryotic cells may have once lived in symbiosis with prokaryotic cells and over time may have evolved into organelles of the eukaryotes specifically mitochondria and chloroplasts

The Endosymbiont Theory

Evidence • Factors in favor of mitochondrial and chloroplast endosymbiosis. • Outer membrane is similar to the plasma membrane. • Mitochondria look a lot like bacteria; chloroplasts look a lot like blue-green algae. These organelles are similar to prokaryotes in that: – Both have their own DNA. -Both reproduce by fission (independant from the rest of the cell) – Both have prokaryotic type and size ribosomes. – Inner membrane lipids of mitochondria and chloroplasts are similar to their prokaryotic counterparts.

1. • Chemical methods seem most likely and scientists have been able to generate the necessary biomolecules from molecules that were thought to be present on the early earth.

2. • Spontaneous Generation is the idea that life can arise form non-living matter • Biogenesis states that only living things can produce living things

3. • Prokaryotes are simpler organisms than eukaryotic cells

4. • If prokaryotic cells linked symbiotically with early eukaryotic cells they could have been mutually beneficial to each other and eukaryotic cells could have evolved to incorporate prokaryotes likely as mitochondria or chloroplasts