Origins of Life-2

1. Origins of Life-2 Unit 1 Part 1

2. Origins of Life -2 Objectives • Describe the chemical and physical conditions of the pre-biotic Earth • Discuss several theories of the origins of life on Earth. • Describe how the success of prokaryotic life has changed the chemical conditions of this planet. • Discuss how our understanding of the origins of life on Earth is helping us look for life (or the evidence of past life) elsewhere in the universe (discuss examples Mars, Titan, etc.).

3. Earth • The earth is 4.5 to 4.7 Billion Years Old

4. Major landmarks in biological evolution

6. How did we get here? ? Life 0.5-1 billion years No Life ~3.5 billion years ago 4.5 billion years ago

7. Inorganic Organic Cellular organization Progenote Universal Ancestor Pre-life Earth was a mixture of chemicals Elements of life H, O, C, N, S, P, (and a little P, Fe, Na, and K)

8. Theories of the Origins of Life • Spontaneous formation of organic molecules • “RNA” world • Solid-phase “Iron-Sulfur” world

9. Theories about the origin of life on Earth • Spontaneous Formation of Organic Molecules (Oparin and Haldane 1920s) • the combination of reduced gasses and electricity (or UV radiation or nuclear radiation) caused the formation of more complicated organic compounds

10. Spontaneous formation evidence • Urey & Miller experiments (1950s) • Created amino acids, sugars, fatty acids, thioesters, and nucleotide bases in the lab • Amino acids and other organic molecules are found in meteorites (shows that it can happen without human intervention) • Detected in space (spectral analysis)

11. Theories • “RNA world” • RNA has two properties that make it an attractive first polymer of life • Contains information (nucleotide bases) • Catalytic (RNA can do some chemical reactions)

12. The RNA World self-replicates Proteins take over catalysis DNA becomes long term storage and major coding molecule Packaging evolves - RNA codes and catalyses The current “most accepted “theory of life evolving hypothesizes an RNA world RNA in the early world would have functioned as a self replicating molecule, eventually developing a number of minimal catalytic properties RNA

13. Rybozymes The first ribozyme discovered was a piece of mRNA that could self-edit – cut out the introns.

14. Order of the Information Macromolecules DNA RNA Proteins RNA required for protein synthesis (mRNA, tRNA, rRNA) DNA is a modification of RNA Where did the first RNA come from?

15. Ribosymes • The first RNA polymers may have formed on clay templates (clay molecules have very regular structures)

16. Origin of Life • RNA World • -Most accepted theory • -In early world as self-replicating molecule • -Later developing other catalytic properties • Stages of RNA World: • 1-Formation of nucleotides (spontaneous formation?) • 2-Formation of RNA molecules (on clay template?) • 3-RNA replication • RNA molecules that evolve catalytic activities (protein synthesis) had a selective advantage • 4-The link between sequence of RNA and sequence of proteins (translation)

17. The RNA World self-replicates Proteins take over catalysis DNA becomes long term storage and major coding molecule Packaging evolves - RNA codes and catalyses RNA

18. Theories • Solid-phase “Iron-Sulfur” world – life formed on solid surfaces The reaction between Fe+2 and HS- (or H2S) can be coupled to CO2 fixation This type of reaction can occur in high temperature, high pressure environments - hydrothermal vents

19. Iron-sulfur world Evidence • Iron and sulfur are important catalytic elements in biology (oxidation/reduction reactions) • Laboratory demonstrations of the production of pyruvate under “prebiotic” conditions

20. Abiotic reactions leading to organic compounds – occur under high temp/high pressure conditions

21. Cells Inorganic Organic Cellular organization Progenote Universal Ancestor

22. Origin of Cells • Organic molecules have tendency to aggregate • membrane-like structures form easily and even happen in laboratory experiments • Microspheres- " coacervates“- form spontenously and can replicate by pinching off new spheres • Proteinous microspheres with catalytic and self- replicating properties could be formed in the lab (Fox 1965, Protobionts, Progenotes)

23. Coacervate growth and division Collection of aggregated polymers Grow by adding new polymers Form a semi-permeable membrane When they get too big they divide Demonstrates how polymers aggregate and act like membranes

24. Progenote or Protobiont • Proteinaceous microspheres – contain proteins and lipids but no nucleic acids • Self replicating • Some ability to catalyze reactions • “pre-cells” • Progenotes would eventually pick up RNA and DNA, develop enzymatic capabilities and membrane organization = primitive cell

25. Origin of Life

26. Where did life start? • Hydrothermal vents • RNA lineage puts hyperthermophiles nearest to the universal ancestor (see fig 2.3 where are the hyperthermophiles?) • Rich in reduced compounds Fe+2, H2S, H2 etc. • Protected from sterilizing cosmic radiation

27. Where did life start? • “Panspermia” – extraterrestrial – life landed here on a meteorite • Life started earlier than previously thought (when the earth was less than a billion years old) • Organic material is found in meteorites • Life exists on earth in habitats similar to those found (or once existed) on Mars, Europa, Titan

28. Magnetite crystals

29. The first organism must have employed a simple strategy to obtain energy. Primitive metabolism was anaerobic, and likely chemolithotrophic, exploiting the abundant sources of FeS and H2S present. One possibility is FeS + H2S ==> FeS2 + H2 The resulting H2 could have been used to drive a primitive ATPase with S0 asa potential electron acceptor Brock pg 428 Fermentations, and anaerobic respiration probably appeared later along with anoxygenic photosynthesis followed by oxygenic photosynthesis. The latter led to development of an oxic environment, and to great bursts of biological evolution.

30. Oxygen • Earliest Evidences: oldest fossils • Oldest photosynthetic microbes 3.5-3.2 B.Y. • - Bacterium-like • - Unicellular • - Evidence for breakdown products of photosynthesis • Cyanobacteria, 3.5 B.Y. • Stomatolites, 3.5- 0.7 B.Y.

31. Oxygen Evidence for O2 production: • Banded Iron Formations (BIF) • BIF found in ocean sediments red bands are high in Fe2O3 and Fe3O4 (red bands)- forms when reduced iron reacts with O2

32. Oxygen

33. Oxygen • Only known source of O2 in the atmosphere is oxygen producing photosynthesis • Photosynthesis produced O2 in the oceans that combined with the Fe producing iron oxides-sinking down to ocean floor producing BIF • BIFs occur in geological rock formations dating back to 3.2-2 B.Y.

34. Life on Earth

35. Oxygen • BIFs occur 3.2-2 B.Y. ago, suddenly disappear. • Red beds, terrestrial formations similar to BIF, but much lower in iron concentrations • Red beds, indication of presence of O2 in the atmosphere • Red beds are present in terrestrial sediments in last 2 B.Y. • Formation of red beds beginning 2B.Y. ago, after all reduced Fe in the oceans had been oxidized

36. Life on Earth Oxygen sinks: • Volcanic gases scavenge O2 • Aerobic respiration uses O2 • Weathering of rocks containing reduced elements such as carbon, sulfur, and iron • Above sinks has not changed since Archean time • But BIFs sink finally became saturated 2 B.Y. ago • Massive iron-rich ores that are used today to make steel are legacy of photosynthetic microbes • Summary: massive change in chemistry of the Earth, mediated entirely by bacteria

37. Why did the availability of oxygen drive evolution (or why are eukaryotes aerobic)? • Hint – see the Nealson 1999 paper.

38. Major landmarks in biological evolution