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Albia Dugger Miami Dade College Chapter 19 Life’s Origin and Early Evolution.

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Presentation on theme: "Albia Dugger Miami Dade College Chapter 19 Life’s Origin and Early Evolution."— Presentation transcript:

1 Albia Dugger Miami Dade College Chapter 19 Life’s Origin and Early Evolution

2 19.1 Looking for Life Astrobiology is the study of life’s origins and distribution – astrobiologists study Earth’s extreme habitats to determine the range of conditions living things can tolerate Life on Earth is protected by the ozone layer, which serves as a natural sunscreen, preventing most UV radiation from reaching the planet’s surface Life can adapt to nearly any environment with sources of carbon and energy – including extreme temperatures, pH, salinity, or pressure

3 Lessons from Chile’s Atacama Desert

4 19.2 The Early Earth Knowledge of modern chemistry and physics are the basis for scientific hypotheses about early events in Earth’s history

5 Origin of the Universe and Our Solar System Big bang theory The universe began in an instant, 13-5 billion years ago All existing matter and energy suddenly appeared and exploded outward from a single point The universe is still expanding Earth formed from dust and debris orbiting the sun, about 4.6 billion years ago

6 Formation of the Earth

7 Conditions on the Early Earth Earth’s early atmosphere came from gas released by volcanoes, and was low in oxygen Rain washed minerals and salts out of rocks to form early seas

8 ANIMATION: Origin of organelles To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

9 Early Earth

10 Take-Home Message: What were conditions like on the early Earth? Earth’s early atmosphere had little or no oxygen Meteorites pummeled the planet’s surface, and volcanic activity was more common than it is today

11 19.3 Formation of Organic Monomers All living things are made from the same organic subunits: amino acids, fatty acids, nucleotides, and simple sugars Small organic molecules that serve as building blocks of life can be formed by nonliving mechanisms

12 Possible Sources of Life’s First Building Blocks 1.Stanley Miller showed that amino acids form in conditions that simulate lightning in the atmosphere of early Earth 2.Wächtershäuser and Huber synthesized amino acids in a simulated hydrothermal vent environment 3.Amino acids, sugars, and nucleotide bases may have formed in interstellar clouds and been carried to Earth on meteorites

13 boiling water gases water in spark discharge electrodes water droplets water containing organic compounds liquid water in trap CH 4 NH 3 H 2 O H 2 to vacuum pump condenser water out Figure 19-4 p311

14 A Hydrothermal Vent on the Seafloor

15 Take-Home Message: What was the source of organic molecules to build the first life? Small organic molecules that serve as the building blocks for living things can be formed by nonliving mechanisms. For example, amino acids form in reaction chambers that simulate conditions on the early Earth, and are present in some meteorites

16 ANIMATED FIGURE: Miller's reaction chamber experiment To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

17 19.4 From Polymers to Protocells We will never know for sure how the first cells came to be, but we can investigate the possible steps on the road to life

18 Properties of Cells All living cells carry out metabolic reactions, are enclosed within a plasma membrane, and can replicate themselves Cells have a genome of DNA that enzymes transcribe into RNA, and ribosomes that translate RNA into proteins Studies support the hypothesis that cells arose from a stepwise process that began with inorganic materials

19 inorganic molecules …self-assemble on Earth and in space organic monomers …self-assemble in aquatic environments on Earth organic polymers …interact in early metabolism …self-assemble as vesicles …become the first genome protocells in an RNA world …are subject to selection that favors a DNA genome DNA-based cells Figure 19-6 p312

20 Origin of Metabolism Before cells, nonbiological process that concentrate organic subunits might increase the chance of polymer formation Concentration of molecules on clay particles in tidal flats may have caused organic subunits to bond as polymers The iron–sulfur world hypothesis holds that the first metabolic reactions began on the surface of rocks around hydrothermal vents

21 Origin of the Genome An RNA-based system of inheritance may have preceded DNA-based systems RNA world hypothesis RNA may have stored genetic information and functioned like an enzyme in protein synthesis RNAs that function as enzymes (ribozymes) are common in living cells today

22 Origin of the Plasma Membrane The cell’s plasma membrane allows organic molecules to concentrate and undergo reactions Membranous sacs (protocells) containing interacting organic molecules may have formed prior to the earliest life forms In experiments, small organic molecules can react with minerals and seawater to form vesicles with a bilayer membrane

23 Laboratory-Produced Protocells

24 Testing a Hypothesis

25 Take-Home Message : What do experiments reveal about steps that led to the first cells? All living cells carry out metabolic reactions, are enclosed within a plasma membrane, and can replicate themselves Metabolic reactions may have begun when molecules became concentrated on clay particles or in tiny rock chambers near hydrothermal vents RNA can serve as an enzyme, as well as a genome. An RNA world may have preceded evolution of DNA-based genomes Vesicle-like structures with outer membranes form spontaneously when certain organic molecules are mixed with water

26 19.5 Life’s Early Evolution Fossils and molecular comparisons among modern organisms inform us about the early history of life

27 Origin of Bacteria and Archaea Life that arose 3-4 billion years ago was probably anaerobic and used dissolved carbon dioxide as a carbon source Early fossil cells are similar in size and structure to modern archaea and bacteria The first photosynthetic cells were bacteria that used the cyclic pathway (does not produce O 2 )

28 Fossil Prokaryotic Cells

29 The Proterozoic Era The oxygen-producing, non-cyclic pathway of photosynthesis first evolved in cyanobacteria In the Proterozoic era Layers of photosynthetic bacteria formed large dome-shaped, layered called stromatolites Oxygen accumulation in air and seas halted spontaneous formation of molecules of life, formed a protective ozone layer, and spurred evolution of organisms using aerobic respiration

30 Stromatolites

31 The Rise of Eukaryotes The earliest evidence of eukaryotes is lipids in 2.7-billion- year-old rocks – the lipids are biomarkers for eukaryotes A red alga that lived 1.2 billion years ago is the oldest species known to reproduce sexually, a trait unique to eukaryotes Multicellularity and cellular differentiation allowed evolution of larger bodies with specialized parts Spongelike animals evolved about 870 million year ago; animals with more complex bodies existed about 570 mya

32 Fossils of Some Early Eukaryotes

33 Take-Home Message: What was early life like and how did it change Earth? Life arose by 3–4 billion years ago; it was probably anaerobic and did not have a nucleus An early divergence separated ancestors of modern bacteria from the lineage that lead to archaea and eukaryotic cells The first photosynthetic cells were bacteria that used the cyclic pathway; later, the oxygen-producing, noncyclic pathway evolved in cyanobacteria Oxygen accumulation in air and seas halted spontaneous formation of the molecules of life, formed a protective ozone layer, and favored organisms that carried out the highly efficient pathway of aerobic respiration

34 19.6 How Did Eukaryotic Traits Evolve? Eukaryotic cells have a composite ancestry, with different components derived from different lineages Archaea-like nuclear genes govern genetic processes (DNA replication, transcription, translation) Bacteria-like nuclear genes govern metabolism and membrane formation

35 Origins of Internal Membranes In eukaryotes, DNA resides in a nucleus bordered by a nuclear envelope – a double membrane with pores that control the flow of material into and out of the nucleus A few modern bacteria also have internal membrane- enclosed compartments The nucleus and endomembrane system probably evolved from infoldings of plasma membrane

36 19-10a p1910 nuclear envelope infolding of plasma membrane ER

37 Bacteria with Internal Membranes

38 Evolution of Mitochondria and Chloroplasts The endosymbiont hypothesis holds that mitochondria and chloroplasts descended from bacteria that were prey or parasites of early eukaryotic cells Mitochondria are genetically similar to aerobic bacteria called rickettsias; chloroplasts are similar to photosynthetic bacteria called cyanobacteria

39 Rickettsia prowazekii

40 Evidence of Endosymbiosis Endosymbiosis can occur when a bacterium infects a eukaryotic cell Eventually, host and symbiont become incapable of living independently Example: The photosynthetic organelles of glaucophytes are dependent on their host – they can’t survive on their own

41 Figure 19-12a p317 photosynthetic organelle that resembles a cyanobacterium

42 Figure 19-12b p317 photosynthetic organelle that resembles a cyanobacterium

43 Take-Home Message: How might eukaryotic organelles have evolved? A nucleus and other organelles are defining features of eukaryotic cells The nucleus and ER may have arisen through modification of infoldings of the plasma membrane Mitochondria and chloroplasts most likely descended from bacteria

44 19.7 Time Line for Life’s Origin and Evolution

45 Table 19-1 p320

46 ANIMATION: Evolutionary tree of life To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

47 ANIMATED FIGURE: Milestones in the history of life To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE


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