Evolution of self-replicating RNA? Incubate billions of randomly generated RNAs with labeled ribonucleotides. Select labeled molecules, replicate (with mutation). Repeat. After 18 rounds of selection: Can catalyze RNA polymerization faithfully. But not self-replication…rather replication of other RNA! Johnston et al. 2001 Science

The origin of life on earth required the formation of larger macromolecules such as polypeptides from smaller organic molecules. the formation of cell-like structures that enclosed basic metabolic processes and a hereditary mechanism. DNA to transmit information from parent to offspring. All of the above. A and B.

Steps in the Origin of Life (Oparin-Haldane Theory) organic molecules form can occur spontaneously (Miller-Urey experiment) ex: amino acids, nitrogenous bases (part of DNA/RNA) macromolecules polymerize minerals may have acted as a template ex: proteins, nucleic acids membrane-enclosed protocells form can occur spontaneously under laboratory conditions a hereditary mechanism develops RNA as both enzyme and genetic material While the original Oparin-Haldane Theory implied that these events must have occurred in the listed order, more recent work (see reading) provides alternatives to the order of events in the origin of life.

06 Life on Earth First evidence for life: stromatolites & microfossils Oxygenic photosynthesis banded iron formations oxygen revolution endosymbiosis theory of eukaryotic development multicellular organisms in Ediacaran Cambrian explosion

Stromatolites (varying evidence of existence beginning 3 Stromatolites (varying evidence of existence beginning 3.45 BYA or more recently at 2.7 BYA) Campbell 8th, Figure 25.1, www2.fiu.edu/~longoria/gly1101/proterozoic.html

Microscopic fossils of bacteria or cyanobacteria from several sites, dated to 2.7–2.5 BYA Figure 3. ca 2500–2700 Myr old Archaean microfossils photographed in petrographic thin sections. (a–e) Broad prokaryotic (oscillatoriacean cyanobacterium-like) tubular sheaths (Siphonophycus transvaalense) from the ca 2516 Myr old Gamohaan Formation of South Africa (Klein et al. 1987; Buick 2001); scale for parts (a) and (b) shown in (b); scale for parts (c) and (d ) shown in (c). ( f–k) Solitary and paired (denoted by arrows) prokaryotic (bacterial or cyanobacterial) coccoidal unicells and (l–q) solitary and paired (denoted by arrows) bacterium-like rod-shaped unicells from the ca 2600 Myr old Monte Cristo Formation of South Africa (Lanier 1986; Buick 2001); scale for parts ( f–q) shown in ( f ) (modified after Lanier 1986). (r) Narrow prokaryotic (bacterial or cyanobacterial) septate filament and (s) broad sheath-enclosed prokaryotic (oscillatoriacean cyanobacterium-like) septate filament from the ca 2723 Myr old Tumbiana Formation of Western Australia (Schopf &Walter 1983). 2.5-2.7 Ga microfossils (Schopf, 2006. Phil. Trans. R. Soc. B 361: 869-885)

Cyanobacteria were the first organisms to perform oxygen-producing (oxygenic) photosynthesis Freeman 4th, Figure 28.10

Canfield (2005) Ann. Rev. Earth Planet. Sci. 33: 1-36 Atmospheric oxygen spiked after cyanobacteria became prevalent: The Oxygen Revolution % Present Day O2 Levels Canfield (2005) Ann. Rev. Earth Planet. Sci. 33: 1-36 8

Banded Iron Formations (Image courtesy of Dr. Pamela Gore, Georgia Perimeter College) (Hayes, 2002, Nature 417: 127-128)

Early Life, Photosynthesis and O2 Relative abundance of Banded Iron Formations Canfield (2005) Ann. Rev. Earth Planet. Sci. 33: 1-36

What caused atmospheric O2 to be present? O2 is formed by photosynthesis and consumed by respiration: CO2 + H2O  “CH2O” + O2 “CH2O” + O2  CO2 + H2O

Atmospheric O2 and the Ocean Most organic matter (“CH2O”) produced is respired quickly. Fig: Canfield (2005) Ann. Rev. Earth Planet. Sci. 33: 1-36

Oxygen Revolution is the greatest atmospheric pollution event on record. It fundamentally changed the oceanic and atmospheric conditions on earth. % Present Day Levels Atmospheric O2 and major biological events Earliest photosynthetic bacteria: ~ 2.5 BYA Earliest eukaryotes: ~ 2 BYA Multicellular organisms: ~ 0.6 BYA 13

At the beginning of the oxygen revolution, you would predict that cyanobacteria populations were Dying off Remaining steady in size. Increasing in size. No predictions can be made.

The accumulation of substantial quantities of free O2 in our atmosphere A. occurred with an increase in organic carbon in the atmosphere. B. created ideal conditions for the spread of anaerobic organisms. C. allowed the previously dominant species of non-photosynthetic bacteria to occupy new habitats and increase their population sizes. D. Was caused by the evolution of oxygenic photosynthesis. E. C and D.

Campbell & Reece 7th Edition, Fig. 25.18 All organisms we know of on Earth today are descended from a “common ancestor” that lived about 4 billion years ago. Over time, three domains arose. 4 Symbiosis of chloroplast ancestor with ancestor of green plants 3 Symbiosis of mitochondrial ancestor with ancestor of eukaryotes 2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells?? 1 Last universal common ancestor (LUCA) of all living things Campbell & Reece 7th Edition, Fig. 25.18

Freeman 4th, Figure 29.8

Endosymbiosis theory for the origin of mitochondria Freeman 4th, Figure 29.9, 29.10

All plants and animals have mitochondria, but only plants have chloroplasts, which enable the formation of chemical energy from light through the same mechanism as in cyanobacteria. The endosymbiosis theory would predict that mitochondria were engulfed first; chloroplasts were engulfed later. chloroplasts were engulfed first; mitochondria were engulfed later. Mitochondria and chloroplasts were engulfed by two separate and independent lineages and do not coexist. Any of these is possible. Either a or b but not c.

Cambrian explosion Opabinia Hallucigenia Image credits: paleobiology.si.edu/burgess/burgessSpecimens.html

II and IV III only II, III, and IV II only all five of these If it were possible to conduct sophisticated microscopic and chemical analyses of microfossils found in 3.2-billion-year-old stromatolites, then within such microfossils, one should be surprised to observe evidence of: I. double-stranded DNA II. a nuclear envelope III. a nucleoid IV. a nucleolus V. nucleic acids II and IV III only II, III, and IV II only all five of these

Which of these observations would fail to support the endosymbiotic theory for the origin of eukaryotic cells? rRNA sequence differences between eukaryotes and mitochondria size differences between some prokaryotic cells and mitochondria No genes in common between prokaryotes and chloroplasts All of these support the endosymbiotic theory.