-Origins-

Vocab review Inorganic Organic Abioitc Catalyst

LUCA What are the characteristics of life? NASA: "A self-sustaining chemical system capable of Darwinian evolution."

Four Stages of the Origin of Life Abiotic synthesis of organic monomers Formaiton of organic polymers Protocells: packaging of molecules into a membrane Living Cells: origin of self-replicating molecules - inheritance

Early Earth: Precambrian *Deep Time* accounts for 87% of the geologic timescale

Formation of the ocean

Oparin-Haldane hypothesis “Primordial” soup aka organic soup hypothesis – Atmosphere had little O 2, but plentiful in H 2 O vapor, H 2 gas, CH 4 and NH 3 – Reducing environment – Abiotic synthesis of organic compounds via redox reaction (oxidation-reduction reactions)

REDOX: transfer of electrons from one molecule to another An electron donator = oxidized, becomes ____ charged…loss = oxidized An electron acceptor = reduced, becomes _____ charged…gain=reduced Important role in biological energy “transactions” Associated with free radicals Abnormal redox states can cause sepsis, hypoxia, shock

1953: Miller-Urey experiment

Hypothesized…organic compounds that formed… No free oxygen present – so no oxidation No bacteria – so no decomposition Washed into ocean = warm, organic soup from which life could arise

Spoiler alert N 2 gas, not NH 3 was more abundant… Repeated experiments with more likely atmospheric recipes have yielded no organic molecules

Pocket Hypothesis Atmosphere near volcanic openings Reducing environments

Replicated deep ocean thermal vent environment, iron-nickel sulfides reduced N 2 to NH 3 in a matter of minutes.

Iron-Sulfur World hypothesis Deep sea thermal vents provided all elements and conditions necessary for abiotic synthesis Iron and Nickel sulfide molecules act as a catalyst Carbon monoxide, ammonia, and hydrogen sulfide are reduced hermal_vent#p00fff1y hermal_vent#p00fff1y

Extra bonus Inorganic iron-nickel sulfides have a charged surface – attract amino acids and bind them together…

Extraterrestrial Origins Hypothesis Organic molecules present in some meteorites Could have seeded chemical origin of life on the planet A martian meteorite had what appeared to be fossilized bacteria present Bacteria from another planet arrived here via meteorite and seeded the whole shebang

Protein first hypothesis Polymerization of amino acids in dry heat, form proteinoids Proteinoids form microspheres Protein enzymes arose before DNA

RNA first hypothesis Need a way to pass down coded information from one generation to the next RNA can carry out enzyme like reactions Ribozymes Can catalyze its own synthesis  proteins associate with it and speed it up Haven’t seen it happen in “the wild” Natural selection can act upon it…

Spoiler alert Nucleotides are complicated Chances that nucleic acids were made spontaneously = immensely unfavorable odds

Membrane-first hypothesis Protocell (protobiont) Outer membrane Why is a membrane critical? – Regulation and maintenance of cellular activities

Other ideas… Various other religious beliefs  Not science. What’s the difference?

Protobionts Groups of abiotically produced molecules surrounded by a “membrane” Simple reproduction and metabolism Maintenance of internal chemical environment, different from surroundings Examples: – Liposomes – Coacervates

Coacervates

Liposomes: Form spontaneously in water

Capable of reproduction and simple metabolism

Simple RNA sequences could carry genetic information RNA could have been a template for DNA

Geology Index fossils and relative dating Absolute dating and radiometric techniques (K-Ar) Fossils Oldest prokaryotic fossils: resemble cyanobacteria

Oxygen in the atmosphere Photosynthetic bacteria (cyanobacteria) Formed ozone when struck by lightning

Endosymbiotic Theory Size, own DNA and some protein production, binary fission, outer membrane resembles bacterial cell

Multicellularity Cell specialization Cells in contact and actions are coordinated

Many questions remain… DNA? Association of RNA with amino acids to build proteins? Electron transport systems for energy transfer? Origins of eukaryotic cells?

1969 Advent of 5 kingdom system

DNA and Protein Sequencing 3 Domain system replaces kingdom monera