AP Biology: Chapter 25: Origin of Life
1 AP Biology: Chapter 25: Origin of Life
2 Emphasize the importance of opening up niches
Watch the HHMI on mass extinction - watch the fist 1/3 of program.
3 Next Slide has this video clip
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http://www.ucsd.tv/miller-urey/ Simulation of experiment
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Comparison of two possible views for the path leading from a 'primordial soup' to a rudimentary protocellular structure (bottom). (A) The 'biopolymer first' scenario, according to which the emergence of self-replicating informational strings such as RNA and proteins are assumed to have had an independent origin from that of lipid encapsulation. (B) The 'Lipid World' scenario, which maintains that the roots of life could have been aggregates of spontaneously assembling lipid-like molecules endowed with capabilities for dynamic self- organization and compositional inheritance. More elaborate structures, including informational and catalytic biopolymers, might then have evolved gradually
However, enzymes are only one way to speed chemical reactions up. Heat is another way to join monomers into polymers. Scientists have shown that when organic monomers (like amino acids) are heated and splashed onto hot sand or rocks, the heat vaporizes the water and links the monomers into polymers - which scientists call 'proteinoids'.
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25 AP Biology: Chapter 25: Origin of Life
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In water, organic chemicals do not necessarily remain uniformly dispersed, but may separate out into layers or droplets. If the droplets which form contain a colloid rich in organic compounds and are surrounded by a tight skin of water molecules then they are known as coacervates. These structures were first investigated by Bungenburg de Jong in 1932. A wide variety of solutions can give rise to them; for example, coacervates form spontaneously when a protein, such as gelatin, reacts with gum arabic.
Coacervate droplets formed by interaction between gelatin and gum arabic. A. I. Oparin. Note: This photo appears on p. 103 of The Origin of Life by Cyril Ponnamperuma (E. P. Dutton & Co., 1972). http://www.daviddarling.info/encyclopedia/C/coacervate.html
COACERVATES, polymer-rich colloidal droplets, have been studied in the Moscow laboratory of A. I. Oparin because of their conjectural resemblance to prebiological entities. These coacervates are droplets formed in an aqueous solution of protamine and polyadenylic acid. Oparin has found that droplets survive longer if they can carry out polymerization reactions. http://www.biog1105-
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1106.org/demos/106/unit04/3a.protobionts.html
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http://www.sciencedirect.com/science/article/pii/S0144861709004925
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PROTOBIONTS... chemically made artificial vesicle systems... aggregates of prebiotic macromolecules that acquire a boundary to maintain an interior chemical environment distinct from "primordial soup"... Sidney W. Fox Univ of Miami (1912 - 1998) - Director of NASA supported Institute for Molecular Evolution at UM. his laboratory conducted analyses of the first moon rock samples... he produced proteinoidsg from amino acid solutions... dropped on hot lava rock,sand or clay
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http://biocab.org/files/PROBABLE_APPEARANCE_OF_AN_EARLY_P ROTOBIONT.jpg
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Ted Talk: http://www.youtube.com/watch?v=dySwrhMQdX4
3:53 – 10:00
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A. RNA can function as an enzyme in cells - called a ribozyme. RNA has been shown to remove its own introns as well as synthesize new RNA (mRNA, rRNA, and tRNA). There are over 500 different ribozymes known today.B. RNA can make a copies of itself in a test tube. If RNA in a test tube is supplied with monomers (ribonucleotides A, C, U and G), sequences 5-10 nucleotides long can be copied from the template according to base-pairing rules. If zinc is added as a catalyst, sequences up to 40 nt long are copied with less than 1% error.In 1989, Tom Cech won the Nobel Prize in Chemistry for his discovery of Ribozymes.: RNA, being capable of self-replication and catalytic, fits one criteria needed life = replicationAll it would take is one protobiont with the ability to replicate, and an inefficient replication process that would generate inevitable copying errors (mutations) to its descendants to produce a diverse population of living cells....Once replication (and its inevitable mistakes, or mutations) was possible, so was evolution (change over time).It is hypothesized that only after a differential reproductive success was seen in cells that stored their genetic 'blueprint" as the more stable molecule DNA did RNA taking on the intermediate role in the translation of genetic material into physical characteristics.
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Image in a pond ith warm and cold regions (kind of like PCR)
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Both disovered ribozymes – Cech in one type of protozoan and Altman in E. coli.
Video of Cech explaining his work: http://www.hhmi.org/biointeractive/enzymes-are-not-proteins-discovery- ribozymes
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Glycolysis – Cytoplasm Common to all cells No oxygen required It’s the first step
Artificial Molecule evolves in the Lab: http://www.newscientist.com/article/dn16382-artificial-molecule-evolves- in-the-lab.html
TimeLine & RNA World http://exploringorigins.org/index.html
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Evidence suggests that life first evolved around 3.5 billion years ago. This evidence takes the form of microfossils (fossils too small to be seen without the aid of a microscope) and ancient rock structures in South Africa and Australia called stromatolites. Stromatolites are produced by microbes (mainly photosynthesizing cyanobacteria) that form thin microbial films which trap mud; over time, layers of these mud/microbe mats can build up into a layered rock structure the stromatolite.Stromatolites are still produced by microbes today. These modern stromatolites are remarkably similar to the ancient stromatolites which provide evidence of some of the earliest life on Earth. Modern and ancient stromatolites have similar shapes and, when seen in cross section, both show the same fine layering produced by thin bacterial sheets. Microfossils of ancient cyanobacteria can sometimes be identified within these layers.
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http://www.snowballearth.org/week13.html
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47 AP Biology: Chapter 26: Eukaryotic Evolution
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Invagination
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Margulis hypothesized that chloroplasts (lower) originated as cyanobacteria (top).
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Lynn Margulis -- Late 1960s
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Ribosomes from bacteria, archaea and eukaryotes (the three domains of life on Earth), have significantly different structures and RNA sequences. These differences in structure allow some antibiotics to kill bacteria by inhibiting their ribosomes, while leaving human ribosomes unaffected. The ribosomes in the mitochondria of eukaryotic cells resemble those in bacteria, reflecting the likely evolutionary origin of this organelle.
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59 AP Biology: Chapter 25: Origin of Life
Paramecium bursaria
Symbiotic chlorella (green algae)
Paramecium bursaria, a single-celled eukaryote that swims around in pond water, may not have its own chloroplasts, but it does manage to "borrow" them in a rather unusual way. P. bursaria swallows photosynthetic green algae, but it stores them instead of digesting them. In fact, the normally clear paramecium can pack so many algae into its body that it even looks green! When P. bursaria swims into the light, the algae photosynthesize sugar, and both cells share lunch on the go. But P. bursaria doesn't exploit its algae. Not only does the agile paramecium chauffeur its algae into well-lit areas, it also shares the food it finds with its algae if they are forced to live in the dark.
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The morphological and evolutionary progression of the volvocales suggests stepwise evolution of multicellularity, starting with colony formation between unicells (e.g. Gonium), then a stepwise progression of cell expansion, division of labor, specialization and tissue differentiation (e.g. Volvox). Despite their morphological differences, the genomes of Chlamydomonas and Volvox are remarkably similar, suggesting that multicellularity requires few genetic changes.
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Last Universal Common Ancestor – Cells, DNA, Membrane, Ribosomes,Cytosol/cytoplasm, ATP,
Ribosome structure No nuclear membranes Introns Pepdidoglycan- Bacteria (Antibiotic will kill) No Pepdicoglycan – Archaeans Membrane – Phospholipids can be branched and even connnected.
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68 AP Biology: Chapter 26: Eukaryotic Evolution
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Two Japanese scientists have discovered a heterotrophic flagellate that engulfs a unicellular green alga that lives freely in the surrounding water. Once inside, the alga loses its flagella and cytoskeleton; the host loses its feeding apparatus; the host switches from heterotrophic to autotrophic nutrition (photosynthesis); the host becomes capable of phototaxis.
T hypothesis that mitochondria and chloroplasts originated as free- living bacteria captured by another cell and essentially enslaved.This week's Science has evidence of this process at work today. A Secondary Symbiosis in Progress? -- Okamoto and Inouye 310 (5746): 287 -- Science. The figure labeled A shows the normal adult Hatena. It has a flagellum, an eyespot (the arrow), and all that green chlorophyll. Turns out, as shown in figure B, the eyespot is inherited by only one daughter cell, as is the green. All that stuff is from a symbiont living within the cell. The eyespot helps the organism move into the light, meaning that the host's movement is controlled by signals from the symbiont.When the cell divides, one side has the symbiont, the other has a very different morphology. It has a feeding apparatus where the symbiont would be if
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it had one, and is predatory. As it hunts for food, if it picks up a Nephroselmis, it doesn't digest it, but integrates it into the host. First, a green cell (step a) divides (b) into one green (c) and one colorless (d) cell. The colorless cell develops a feeding apparatus de novo (d to e) and engulfs a Nephroselmis (e to g). The symbiont plastid develops and the feeding apparatus degenerates (g to a). As we never observed any dividing cell without a symbiont (d) or with an "immature" plastid (h), symbiont acquisition and modification apparently occur within one generation. How many generations the symbiont persists is an open question.As they say:Hatena represents an early stage in the development of an ongoing secondary endosymbiosis.Secondary symbiosis because the symbiont is a cell with chloroplasts in it.These two organisms illustrate one step in a process which would ultimately lead to organisms like the Euglena, which has a persistent secondary symbiosis. It's chloroplasts can be killed off, leaving the organism to hunt for food. The symbiont can regrow under better conditions. Each symbiont has double membranes, rather than a single membrane, indicating that the original symbiont (probably a kinetoplastid) was ingested by the ancestral euglenophyte. At this stage in Hatena's development, the symbiont doesn't divide in synchrony with the host, but that synchrony can evolve, just as the host-symbiont specificity has evolved already.
The DNA in the symbiont shows that it's a member of the genus Nephroselmis. The free living form of the symbiont has morphological differences from the symbiont, but it's abundant where the host occurs.
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