ORIGINS OF LIFE

• Ultimate question for biologists• Many theories/hypotheses/beliefs– Cultural: How is all life connected?– Religious: Is there a creator?– Philosophical: Are we here at all?– Scientific: How could life originate?

• All are valid from each perspective and set of criteria. • However, scientific theory must meet 3 criteria: be based in unbiased research use empirical evidence acquired by observation and

experimentation through scientific method tested over time

What is SPONTANEOUS GENERATION?

• The hypothetical process by which living organisms develop from nonliving matter via a ‘vital force’ in the atmosphere

• An archaic concept, 4th century BC- late 19th century where many people(including scientists)utilized this process to explain the origin of life.

– According to this concept, pieces of cheese and bread wrapped in rags and left in a dark corner were thought to produce mice, because after several weeks there were mice in the rags.

– It was "common knowledge" that simple organisms like worms, frogs, and salamanders could ‘form’ from mud, dust, and unpreserved food.

frog estivation

– Many believed in spontaneous generation because it explained such occurrences as the appearance of maggots on decaying meat.

– Malaria: “bad air” sleeping with windows open made one sick because of the ‘vital force’ in the atmosphere

Experiments to disprove SG…Francesco Redi – 1668- One of the first to try to disprove spontaneous generation. An Italian doctor who proved maggots came from flies, not from meat.

Lazzaro Spallanzani - 1700s - Conducted an experiment with broth to show that the microscopic organisms entered from the air, not by means of spontaneous generation

Critics said by boiling the broth and sealing flasks “vital force” was destroyed…

Rudolf Virchow – 1858- challenged the notion with his theory of “BIOGENESIS”, claiming “all cells come from preexisting cells”. Although correct in his concept he lacked the experimentation to prove it…

Louis Pasteur - 1864 - Conducted an experiment with nutrient broth in curved-neck flasks to finally disprove spontaneous generation

7 SCIENTIFIC ORIGIN THEORIES

Panspermia

Hypothesizes organic molecules and life did not begin on Earth at all, but was brought here from elsewhere in space • Rocks regularly get blasted off Mars by cosmic

impacts• A number of Martian meteorites have been found

on Earth that may have brought microbes to Earth. • Other scientists have hypothesized that life might

have hitchhiked on comets from other star systems.

Community Clay

• The first molecules of life might have formed on clay.

• These sticky reactive surfaces helped:– concentrate organic compounds together–mineral crystals in clay could have arranged

organic molecules into organized patterns.

Chilly Start

Ice that covered the oceans during the last ice age might have protected fragile organic compounds in the water below from ultraviolet light and destruction from cosmic impacts. The cold might have also helped these molecules to survive longer, allowing key reactions to happen.

RNA

DNA needs proteins in order to form, and proteins require DNA to form, so how could these have formed without each other? The answer may be RNA, which can store information like DNA, serve as an enzyme like proteins, and help create both DNA and proteins. Later DNA and proteins succeeded this "RNA world," because they are more efficient. RNA still exists and performs several functions in organisms, including acting as an on-off switch for some genes.

Simple Beginnings

Instead of developing from complex molecules such as RNA, life processes might have begun with smaller molecules interacting with each other in cycles of reactions. These might have been contained in simple capsules akin to cell membranes, and over time more complex molecules that performed these reactions better than the smaller ones could.

Deep-Sea Vents

The deep-sea vent theory suggests that organic molecules and life may have begun at submarine hydrothermal vents, spewing key hydrogen-rich molecules. Their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents, rich in chemical and thermal energy, sustain vibrant ecosystems devoid of energy from the sun.

Electric Spark‘Primordial Soup’

Oparin/Miller-Urey’s apparatus demonstrated that electric sparks can generate simple organic compounds from an atmosphere loaded with water, methane, ammonia and hydrogen. The scientist hypothesized that volcanic clouds holding methane, ammonia and hydrogen together with the energy from lightning could be split and recombined to form organic monomers.

Simple amino acids, nucleotides, nucleic acids formed as elements were rearranged from the energy of lightning

EVAPORATION

PRECIPITATION

RUNOFF

CONDENSATION

Where did the first cells come from?The appearance of the first cells marked the origin of life on Earth. However, before cells could form, the organic molecules had to have united with one another to form more complex molecules called polymers…proteins, lipids, carbohydrates, nucleic acids

Most scientists agree that the biochemistry of life had to come before cellular structures.

Example: Cell Membrane

• Formation of phospholipid• nature of molecule gives it an end that is

attracted to water and an end that is repelled by water

• When these molecules are placed into a watery environment they form….. SPHEREShttp://exploringorigins.org/fattyacids.html

FIRST LIFE4.6 billion years ago

Earth Conditions No free oxygen, toxic

atmosphere, extremes in temperature, pH, cloudy humid, lightning

Earliest LifeAnaerobic heterotrophic

prokaryotes consuming organic molecules

Anaerobic autotrophic (chemosynthetic) prokaryotes

similar to the volcanic vent archaebacteria

Temperatures regulate, less evaporation-less

precipitation-more sun

Oxygen levels rise in atm, ozone forms and cuts UV levels dramatically

Aerobic heterotrophic and autotrophic(photosynthetic)prokaryotes

Heterotrophic eukaryotes

Autotrophic eukaryotes

Prokaryotic to Eukaryotic?Endosymbiont Theory

Cells engulf large nutrient molecules in process called endocytosis…animation

Lynn Margolis’ theory suggests small aerobicprokaryotes were taken in by endocytosis and began to live inside a larger anaerobic prokaryote in an endosymbiotic

relationship….eventually they became the mitochondria and chloroplasts

What evidence supports theory?The mitochondria and chloroplasts:• Only organelles that have a bi-lipid membrane• Have their own genes, DNA different from

nuclear DNA of cell• Replication cycle is independent from the

replication cycle of cell that contains them• Both convert energy(autotrophic/heterotrophic)