Chapter 14 The Origin of Life

The early idea:

Spontaneous Generation- nonliving material can give

rise to life

maggots grow on meat, mud produce fish, mice appear

in sacks of grain

1668-Francesco Redi- disproved that decaying meat produces flies

But, during this time, the microscope got big.  scientists believed that the reason that there were so many bacteria that they must arise spontaneously.

mid-1800s  Louis Pasteur disproved spontaneous generation

of microorganisms

Led to theory of biogenesis: living organisms come only from

other living org.

Modern Theories on the Origin of Life

Biogenesis is accepted as fact, but does not explain how life first arose

            (nobody will ever know for sure, but we have alot of theories!)

2 developments must have preceded life

            A. Simple organic molecules formed

B. Organic molecules became complex macromolecules

(proteins, nucleic , acids, carbs)

            C. Formation of cells

A. Original atmosphere most likely had very little free oxygen- rather water  vapor, carbon dioxide, nitrogen, methane, ammonia- how did they

come together to make organic molecules?

1. 1930s- Alexander Oparin- primordial soup- life began in the ocean when solar energy, lightning, & heat triggered formation of organic  molecules in the atmosphere which then washed into the ocean

2.     1953- Stanley Miller and Harold Urey- simulated conditions

of early Earth in the lab.  Mixed water vapor, ammonia, methane, and hydrogen then zapped it with electrical current (lightning).  The vapors were cooled to produce liquid (rain) and analyzed- amino acids and sugars  were  detected

B. If amino acids are heated without oxygen, they will polymerize = proteins the same process will work for ATP and nucleic acids

            This may have been what happened to form macromolecules

C. Sidney Fox- How the first cells were formed

            heating solutions of amino acids forms protocells- large ordered

structure, enclosed by a membrane, carries out some lifelike

activities- cell division/ growth

The Evolution of Cells

Fossils indicate that photosynthetic prokaryotes existed 3.5 billion years ago

Most likely not the earliest cells

1. Earliest cells may have evolved from the protocell

                        anaerobic, ate organic molecules (heterotrophic)

2. After the food was used up, chemoautotrophs had evolved & were favored

3. Next, photosynthesizing prokaryotes produced oxygen

prokaryotic diversity increased about 2.8 billion years ago

After oxygen was produced, lightning made it ozone, formed the atmosphere, shielded organisms from UV radiation

Endosymbiont Theory

Where did complex cells come from?

1960s- Lynn Margulis- eukaryotes evolved thru symbiosis between prokaryotes

Some present day bacteria are similar to cyanobacteria and

chloroplasts  in size and ability to photosynthesize, some

others resemble mitochondria

Mitochondria and chloroplasts have own DNA and ribosomes