D1 origin of life


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Option D1 IB Biology

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D1 origin of life

  1. 1. Option D: Evolution D1 Origin of life on Earth
  2. 2. What you need to be able to do and understand: D.1.1 Describe four processes needed for the spontaneous origin of life on Earth. D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds. D.1.3 State that comets may have delivered organic compounds to Earth. D.1.4 Discuss possible locations where conditions would have allowed the synthesis of organic compounds. D.1.5 Outline two properties of RNA that would have allowed it to play a role in the origin of life. D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings. D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere. D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes.
  3. 3. Imagine what it would take to create life. What do you need?
  4. 4. Spontaneous origin? If cells can only come from existing cells (the cell theory) when and where did the first cells come from? The oldest undisputed bacteria fossil dates back 1.9 billion years ago Gunflint microfossil Eosphaera 20 microns across. A recipe for cell-like structures: 1. Simple organic molecules need to be available (amino acids need to be made from water, carbon dioxide and ammonia) 2. Simple molecules need to be assembled into polymers (polypeptides from amino acids) 3. A mechanism that makes inheritance possible (self-replication is needed) 4. Development of membranes (to form with an internal chemistry different than their surroundings)
  5. 5. 1- Simple organic molecules Miller and Urey http://bcs.whfreeman.com/thelifewire/ content/chp03/0302001.html They investigated the theory that organic compounds could have formed spontaneously on Earth. Watch this tutorial: In Miller’s own words…
  6. 6. So what did Miller and Urey conclude? Organic compounds could have formed spontaneously on Earth, before there were any living organisms here. http://www.ucsd.tv/miller-urey/ Now do your own experiment to create amino acids
  7. 7. Where were the first organic compounds synthesized? From the experiments of Miller and Urey- in the atmosphere, in water, or on the surface of the Earth Hydrothermal vents with the chemicals from the interior of the Earth Delivered by meteorites. Extraterrestrial origins for organic compounds- NASA conducted experiments showing that organic compounds could have formed in cold interstellar space. Certain categories of meteorites are rich in carbon and some of these meteorites have been found to contain many of the same amino acids found in the Miller-Urey experiment
  8. 8. Data analysis question Read this paper for more information: http://www.lpi.usra.ed u/publications/MSR/B ada/BadaAbs.html Amino Acid Murchison meteorite Miller-Urey experiment Glycine   Alanice   α-amino-N-butyric acid   α-aminoisobutyric acid   Valine   Norvaline   Isovaline   Proline   Popecolic acid   Aspartic acid   N-ethylglycine   Sarcosine   1. Compare the amino acids found in the meteorite with those produced in the Miller-Urey experiment. Refer to named examples [3] 2. Suggest a conclusion based on your comparison. [1]
  9. 9. Hydrothermal vents Another theory suggests that life may have arisen at ancient volcanic vents. This environment provides the necessary gasses, energy, and a possible source of catalysts (metal sulfides). Read this site for a summary of what is known to date: http://www.chem.duke.edu/~jds/cr uise_chem/Exobiology/sites.html
  10. 10. 2- assembled into polymers (polypeptides from amino acids) Polymerization – monomers to polymers
  11. 11. 3- A mechanism that makes inheritance possible (self-replication is needed) RNA almost certainly preceded DNA as the genetic material Self-replication – RNA to RNA RNA has two key abilities that make it the likely original genetic material •genetically: self-replication •enzymatically: catalyzing chemical reactions Read this article on RNA: http://www.nytimes.com/ 2009/05/14/science/14rn a.html Genes cannot be made/ replicated without enzymes and enzymes cannot be made without genes. Therefore how did it all start?
  12. 12. self-replication of RNA RNA has been experimentally shown to have the ability to self-replicate – one molecule can be the template for the production of another molecule. Individual RNA nucleotides self-assemble into RNA polymers because of complementary nucleotide bases A=U G=C RNA nucleotide sequence is variable, thus allowing for diversity. Self-replication allows for the inheritance of information coding for amino acid sequences in polypeptides and transmitting genetic information between generations
  13. 13. RNA can catalyze chemical reactionsRNA can act as an enzyme, catalyzing various reactions, producing polymers from monomers in eukaryotic organisms today. RNA regulates numerous cellular functions, including protein synthesis and gene control. For example, RNA ribozymes are found in modern cell RNA can self- replicate An interview with Dr. Thomas Cech- talking about what RNA can do. He won the Nobel prize in Chemistry in 1989
  14. 14. 4- Development of membranes- creating an internal chemistry different from the external A spherical vesicle composed of a bilayer membrane form spontaneously from phospholipids. coacervates A spherical aggregation of lipid molecules making up a colloidal inclusion which are held together by hydrophobic forces. They form spontaneously from certain dilute organic solutions. Generally 1 to 100 micrometers in diameter and possess osmotic properties. microsphere sThey form spontaneously from heated and cooled amino acids and exhibit some properties associated with life (response to the environment, basic metabolism and simple reproduction) liposom es See for more information: http://www.biog1105- 1106.org/demos/106/unit04/3a.protobionts.html
  15. 15. The result of the recipe?“Protobionts:" the product of the four processes which are cell-like structures. They are an aggregate of abiotically produced organic molecules surrounded by a membrane or a membrane-like structure. Protobionts exhibit some of the properties associated with life, including simple reproduction, metabolism and excitability, as well as the maintenance of an internal chemical environment different from that of their surroundings. Experiments by Sidney W. Fox and Aleksandr Oparin have demonstrated that they may be formed spontaneously, in conditions similar to the environment thought to exist on an early Earth. Fox dripped organic monomers onto hot sand, clay, and rock. The water vaporized and left behind polypeptides he called proteinoids. Clay was abundant in prebiotic earth and has the ability to act as a substrate. The charged sites on the clay attracted monomers in such concentrations to bring them into close proximity for chemical binding. Once these organic compounds were produced, aggregates self-assembled into small spheres called protobionts. These small spheres were capable of osmotic swelling and shrinking and even able to produce a membrane potential. http://www.siuc.edu/~ protocell/
  16. 16. Endosymbiotic theory be eaten and survive… Eukaryotic cells appear to have evolved from prokaryotic ancestry as a smaller prokaryote within a larger prokaryote and then coexisted. Evidence: Mitochondria and chloroplasts both have double membranes where the second outer membrane is from the host, therefore it might have been “eaten”.Mitochondria and chloroplasts both have a loop of naked DNA that lacks histone proteins, as do prokaryotes. Mitochondria and chloroplasts both divide by binary fission which is independent of nuclear division. Mitochondria and chloroplasts both have smaller 70S ribosomes which are similar to prokaryotes and different from 80S eukaryotic ribosomes. Chloroplast thylakoids are similar to cyanobacterial photosynthetic structures. Chlorophyll a is the main photosynthetic pigment for both chloroplasts and prokaryotes.
  17. 17. What did prokaryotes give to us? The first pollution crisis However, oxygen is a powerful degrader of organic compounds. Even today, many bacteria and protists are killed by oxygen. Organisms had to evolve biochemical methods for rendering oxygen harmless; one of these methods, oxidative respiration, had the advantage of producing large amounts of energy for the cell, and is now found in most eukaryotes. Where was this oxygen coming from? Cyanobacteria, photosynthetic organisms that produce oxygen as a byproduct, had first appeared 3.5 billion years ago, but became common and widespread in the Proterozoic era. The first "pollution crisis" hit the Earth about 2.2 billion years ago. Several pieces of evidence -- the presence of iron oxides in paleosols (fossil soils), the appearance of "red beds" containing metal oxides, and others -- point to a fairly rapid increase in levels of oxygen in the atmosphere at about this time. Holland, H.D. 1994. Early Proterozoic atmospheric change. Pp. 237-244. In: Bengtson, S. (ed.) Early Life on Earth. Columbia University Press, New York. Oxygen levels in the Archaean had been less that 1% of present levels in the atmosphere, but by about 1.8 billion years ago, oxygen levels were greater than 15% of present levels and rising. (Holland, 1994). It may seem strange to call this a "pollution crisis," since most of the organisms that we are familiar with not only tolerate but require oxygen to live.
  18. 18. A good summary of everything we have done so far: http://www.plosbiology.org/article/info: doi/10.1371/journal.pbio.0030396 When Art and Science collide, you get the Big Bang and the Origins of Life, as interpreted by the amazing street art animators, Blu.