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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 26 The Tree of Life.

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Presentation on theme: "Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 26 The Tree of Life."— Presentation transcript:

1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 26 The Tree of Life

2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1. How Life Began Geological events that alter environments – Change the course of biological evolution Conversely, life changes the planet that it inhabits Figure 26.1

3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Conditions on early Earth made the origin of life possible Hypothesis: – Chemical and physical processes on early Earth produced very simple cells through a sequence of stages

4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1. Atmosphere Earth formed ~ 4.6 billion years ago Earths early atmosphere – Contained water vapor + many chemicals released by volcanic eruptions – Little or no O 2 reducing atmosphere – But it did have: CO, CO2, H2, N2, H2O, S, and HCl,

5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. SEAS First organic compounds may have formed near submerged volcanoes and deep-sea vents Figure 26.3

6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As material circulated through the apparatus, Miller and Urey periodically collected samples for analysis. They identified a variety of organic molecules, including amino acids such as alanine and glutamic acid that are common in the proteins of organisms. They also found many other amino acids and complex, oily hydrocarbons. RESULTS Figure 26.2 Miller and Urey set up a closed system in their laboratory to simulate conditions thought to have existed on early Earth. A warmed flask of water simulated the primeval sea. The strongly reducing atmosphere in the system consisted of H 2, methane CH 4 ), ammonia ( NH 3 ), and water vapor. Sparks were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and any dissolved compounds into the miniature sea. EXPERIMENT Electrode Condenser Cooled water containing organic molecules H2OH2O Sample for chemical analysis Cold water Water vapor CH 4 H2H2 NH 3 CONCLUSION Organic molecules, a first step in the origin of life, can form in a strongly reducing atmosphere. 3. Complex Molecules Lab simulations of early Earth atmosphere:

7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some organic cmpds. may have come from space Carbon cmpds. have been found in some of the meteorites

8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4. Abiotic synthesis of polymers Small organic molecules – Polymerize when they are concentrated on hot sand, clay, or rock

9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5. Protobionts – Aggregates of abiotically produced molecules surrounded by membrane

10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Protobionts could have formed spontaneously from abiotically produced organic cmpds e.g., small membrane-bounded droplets called liposomes form when lipids are added to water

11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 20 m (a)Simple reproduction. This lipo- some is giving birth to smaller liposomes (LM). (b)Simple metabolism. If enzymesin this case, phosphorylase and amylaseare included in the solution from which the droplets self-assemble, some liposomes can carry out simple metabolic reactions and export the products. Glucose-phosphate Phosphorylase Starch Amylase Maltose Phosphate Figure 26.4a, b

12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings RNA molecules (ribozymes) catalyze many different reactions, including – Self-splicing – Making copies of short stretches of their own sequence Figure 26.5 Ribozyme (RNA molecule) Template Nucleotides Complementary RNA copy 3 5 5

13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Early protobionts with self-replicating, catalytic RNA – used resources and increased in number through natural selection

14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6. Heterotrophs As prokaryotes evolved, they exploited and changed young Earth Oldest known fossils are stromatolites – Rocklike structures w/ many layers of bacteria and sediment – 3.5 billion years old

15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lynn Margulis (top right), of the University of Massachussetts, and Kenneth Nealson, of the University of Southern California, are shown collecting bacterial mats in a Baja California lagoon. The mats are produced by colonies of bacteria that live in environments inhospitable to most other life. A section through a mat (inset) shows layers of sediment that adhere to the sticky bacteria as the bacteria migrate upward. Some bacterial mats form rocklike structures called stromatolites, such as these in Shark Bay, Western Australia. The Shark Bay stromatolites began forming about 3,000 years ago. The inset shows a section through a fossilized stromatolite that is about 3.5 billion years old. (a) (b) Figure 26.11a, b

16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prokaryotes were Earths sole inhabitants – From 3.5 to about 2 billion years ago

17 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electron transport systems of a variety of types – Essential to early life – Some aspects that possibly precede life itself

18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 7. Photosynthesis Earliest types of photosynthesis – Did not produce O 2 – Cyanobacteria are autotrophic prokaryotes that obtain their energy and manufacture organic compounds by photosynthesis

19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8. Oxygen Revolution Oxygenic photosynthesis – Evolved ~ 3.5 bya in cyanobacteria Figure 26.12

20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings O 2 began to accumulate in the atmosphere ~ 2.7 bya – Challenge for life – Opportunity to gain energy from light – Allowed organisms to exploit new ecosystems

21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As the ozone formed the UV light was absorbed by the atmosphere disrupting the energy available for abiotic synthesis of organic compounds.

22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 9. Eukaryotes Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes

23 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oldest fossils of eukaryotic cells – 2.1 billion years

24 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endosymbiosis – Mitochondria and plastids were formerly small prokaryotes living within larger host cells

25 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Probably undigested prey or internal parasites Figure Cytoplasm DNA Plasma membrane Ancestral prokaryote Infolding of plasma membrane Endoplasmic reticulum Nuclear envelope Nucleus Engulfing of aerobic heterotrophic prokaryote Cell with nucleus and endomembrane system Mitochondrion Ancestral heterotrophic eukaryote Plastid Mitochondrion Engulfing of photosynthetic prokaryote in some cells Ancestral Photosynthetic eukaryote

26 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Eventually host and endosymbionts would have become a single organism

27 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Supporting evidence: – Similar inner membrane structures and functions – Both have their own circular DNA (genes) – Own ribosomes

28 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chinese paleontologists recently described 570-million-year-old fossils – probably animal embryos Figure 26.15a, b 150 m 200 m (a) Two-cell stage (b) Later stage

29 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The first multicellular organisms were colonies – Collections of autonomously replicating cells Figure m

30 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some cells in the colonies – Became specialized for different functions The first cellular specializations – Had already appeared in the prokaryotic world


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