1. IB Biology Option D D1 Origin of Life on Earth All syllabus statements ©IBO 2007 All images CC or public domain or link to original material, IB Biology Option D D1 Origin of Life on Earth All syllabus statements ©IBO 2007 All images CC or public domain or link to original material, http://www.flickr.com/photos/euthman/216030298/

2. D.1.1 Describe four processes needed for the spontaneous origin of life on Earth 1)The non-living synthesis of simple organic molecules Obviously if nothing was alive yet then the source of these molecules had to be abiotic We can presume that the early Earth had all of the base elements and compounds required They were somehow combined to make simple organic compounds Maybe the organic compounds were generated here, maybe they were extra-terrestrial! 2)The assembly of these molecules into polymers It makes sense, to make the larger molecules necessary for life, the simple organic compounds would have to polymerise 3)The origin of self-replicating molecules made inheritance possible DNA can’t self replicate, it needs protein enzymes However some RNA can self-replicate, it can catalyse the formation of copies of itself. Short RNA molecules that can duplicate others have been artificially produced in the lab. The shortest was 165-bases long They are called Ribozymes and are the basis of the RNA World Hypothesis 4)The packaging of these molecules into membranes with internal chemistry different from their surroundings The formation of closed membranes an important step Closed membrane vesicles can form spontaneously from lipids. This allowed differentiation between the internal and external environments http://exploringorigins.org/resources.html

3. D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds Earth’s atmosphere was ‘reducing’ in the early days. It did not contain oxygen gas until after plants started photosynthesising All molecules public domain from Wikimedia Commons, Background image http://www.flickr.com/photos/lrargerich/4587244190/http://www.flickr.com/photos/lrargerich/4587244190/ Can you identify these molecules?

4. D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds Earth’s atmosphere was ‘reducing’ in the early days. It did not contain oxygen gas until after plants started photosynthesising The atmosphere contained: Hydrogen Nitrogen Water vapour Methane (CH 4 ) Ammonia (NH 3 ) Hydrogen sulfide (H 2 S) All molecules public domain from Wikimedia Commons, Background image http://www.flickr.com/photos/lrargerich/4587244190/http://www.flickr.com/photos/lrargerich/4587244190/ The gases came from abundant volcanic activity

5. These monomers mixed in the ‘primordial soup’, shallow oceans laden with chemicals where it is thought that they reacted to form biological molecules Miller and Urey tried to recreate these conditions in the lab in 1953 They were trying to demonstrate ‘chemical evolution’, the formation of more complex molecules from simpler stock in the primeval soup They combined the molecules from the previous page in a closed glass vessel (simulated atmosphere), they heated the water (simulated volcanic activity) and sparked electricity through the gases (simulated lightning) http://www.flickr.com/photos/afeman/663646181/

6. Miller and Urey In 1953, Stanley Miller and Harold Urey tested the Oparin-Haldane Hypothesis using the conditions of pre- biotic Earth.

7. A.A warm flask of water simulated the primeval sea B.The atmosphere consisted of H 2 O, H 2, CH 4, and NH 3. C.Sparks were discharged to mimic lightning D.A condenser cooled the atmosphere, raining water and any dissolved compounds back to the miniature sea. E.As material circulated through the apparatus the solution in the flask changed from clear to murky brown F.After 1 week the contents of the flask were examined and found a variety of organic compounds including 13 of the twenty naturally occurring amino acids that make up proteins of organisms.

8. What are their conclusions? Organic compounds (amino acids) were formed from inorganic compounds. Organic compounds could have existed on pre- biotic Earth. Life might have arisen from non-living material.

9. D.1.2 Purpose: To test the hypothesis that organic molecules can form spontaneously under the right conditions. Gases used: ammonia, methane, hydrogen, which created a reducing atmosphere. – Water, heat, as well as a spark to simulate lightning was also used. It worked. 13 of the 20 amino acids were found as well as simple organic molecules.

10. Around 15% of the carbon was now in organic compounds

11. http://www.flickr.com/photos/12057715@N00/354536849/ D.1.3 State that comets may have delivered organic compounds to Earth Panspermia is the hypothesis that life on Earth originated from material delivered by a comet, either in the form of amino acids or as hardy bacteria *Hundreds of meteorites and comets hitting the early Earth brought with them organic molecules formed by abiotic reactions in outer space. **Extraterrestrial organic compounds, including amino acids, have been found in modern meteorites, and it seems likely that these bodies could have seeded the early Earth with organic compounds. Space is so empty, yet full of the potential for life

12. http://www.flickr.com/photos/12057715@N00/354536849/ D.1.3 State that comets may have delivered organic compounds to Earth Existing bacteria and archaebacteria have been found in extreme environments on Earth: In hot springs, kilometers deep in the crust and even embedded in ice cores from deep inside Antarctica It is feasible that they could survive on or in a comet Space is so empty, yet full of the potential for life

13. Cosmic radiation could provide the energy for reactions that lead to the formation of complex organic molecules Analysis of the spectra of light coming from the comets reveals the presence of hydrocarbons, amino acids and peptides The bombardment of Earth by comets 4 billion years ago could have ‘kick started’ chemical evolution http://www.flickr.com/photos/jpstanley/2030855518/ http://www.youtube.com/watch?v=51V363V1bkI

14. D.1.3 Discuss possible locations where conditions could have allowed the synthesis of organic compounds (3 examples) 1)Hydrothermal vents Problem: The water in the Miller Urey experiment tends to hydrolyze (break apart) any polymers as they form and prevents their formation. The conditions in the ocean not ideal for polymerization Solution: “black smokers”, hydrothermal vents where superheated steam escapes from within the crust. The outflow is full of dissolved sulfides that crystallize around the vent and may be a suitable environment for the formation and concentration of complex biological compounds http://www.flickr.com/photos/noaaphotolib/5014975047/sizes/l/in/photostream/ http://www.youtube.com/watch?v=D69hGvCsWgA

15. 2) Volcanoes may also have played a part: Gases from above hot lava lakes have been found to contain a higher than average level of fixed nitrogen Nitrogen fixation is the formation of ammonia (NH 4 ) from nitrogen gas (N 2 ). The Haber process is a modern industrial way to fix nitrogen and it requires high pressures (200 atm) and high temperatures (400 °C) The hypothesis that life originated on Earth is called abiogenesis (ab bio genesis) (aboriginal – life – creation) http://www.flickr.com/photos/storm-crypt/3043902298/ http://exploringorigins.org/fattyacids.html# Volcanoes and geysers may have provided a suitable location for the formation of biological compounds

16. 3) extraterrestrial source: http://images.cdn.fotopedia.com/flickr-2406913018-hd.jpg As previously mentioned, organic molecules are out there Mars is smaller than Earth and therefore cooled down more quickly, life could have begun there while Earth was still scorching Meteorites and comets impacting on mars could have thrown up debris with early life attached, this could then have crashed on Earth. Meteorites of Mars origin have been found in Antarctica There is no evidence that life has been transferred in this way. Every now and then there is a news story about “Fossils found in Mars meteorite” but so far this has not been confirmed The extraterrestrial hypothesis still doesn’t address how life formed, just how it could move around the galaxy

17. D.1.5 Outline Two properties of RNA that would have allowed it to play a role in the origin of life http://genetics.mgh.harvard.edu/szostakweb/exploringOriginsDownloads/centralDogma.jpg RNAs can store, transmit and replicate genetic Information RNA is thought to have served as the first genes, not DNA. DNA  RNA  Proteins: the mechanisms for this is too complicated to have evolved all at once. Genes cannot be replicated without enzymes, and enzymes cannot be made without genes. The first genes were short strands of RNA that began self-replicating in the prebiotic world http://www.youtube.com/watch?v=Mo2DJ1dIoeg

18. D.1.5 Outline Two properties of RNA that would have allowed it to play a role in the origin of life http://genetics.mgh.harvard.edu/szostakweb/exploringOriginsDownloads/centralDogma.jpg Ribozymes are RNA molecules that can catalyse reactions (Hey! You told us that all enzymes are proteins! Liar!) Some can polymerize nucleotides using ATP Some can break chemical bonds, including peptide bonds Ribosomes are themselves Ribozymes (huh?). The part that catalyses the peptide bonds is RNA, the protein part of a ribosome seems to have a purely structural function RNA can catalyze the formation of more RNA (rRNA, tRNA, and mRNA) RNA can bind amino acids and form peptide linkages RNA can transcribe into DNA using reverse transcriptase Ribozymes are an example of a living fossil. Evolution by natural selection requires variation and heritability. RNA possesses these traits

19. D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings (Proto = first, or precursor) Coacervates are droplets of polymeric molecules. Coacervates containing enzymes can absorb and concentrate substrate molecules and then release the products to their surrounds If they absorb a lot of material they can divide into two smaller coacervate droplets This is not true reproduction though so they are not alive. http://exploringorigins.org/protocells.html An illustration of a protocell, composed of a fatty acid membrane encapsulating RNA ribozymes.

20. D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings (Proto = first, or precursor) This is biochemical evolution. Protobiont: A protobiont is an aggregate of abiotically produced organic molecules surrounded by a membrane or a membrane-like structure. Coacervates are droplets of polymeric molecules. Coacervate droplets self-assembles when a solution of polypeptides, nucleic acids, and polysaccharides is shaken. Coacervates containing enzymes that can absorb and concentrate substrate molecules and then release the products to their surroundings Coacervates can contain polynucleotides (RNA) Assembly of chains of amino acids can form proteins Alignment of lipids and the formation of a membrane Synthesis of ATP and anaerobic respiration If they absorb a lot of material they can divide into two smaller coacervate droplets This is not true reproduction though so they are not alive. http://exploringorigins.org/protocells.html An illustration of a protocell, composed of a fatty acid membrane encapsulating RNA ribozymes.

21. Protobionts may have arisen from coacervates. Coacervates containing RNA may have started synthesising proteins Enzyme controlled binary fission may have arisen. The first true cells probably heterotrophic (maybe getting energy from sulfur chemistry) and anaerobic (there was no free oxygen) Microspheres: are another candidate for a structure that might have given rise to protobionts. They form when amino acids are heated and polymerise to form simple proteins (thermal proteins) http://www.daviddarling.info/encyclopedia/M/microsphere.html One milligram of thermal proteins can make 100 million microspheres! They divide like coacervates and can catalyse some reactions

22. D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere Remember: there was little free oxygen in the early atmosphere Small amounts were made by UV light splitting water vapour in the atmosphere The oxygen concentration rose to 0.45% of the atmosphere Not much compared to today’s 21%, but it coincides with the rise of the Eukaryotes COINCIDENCE? Probably not. The increase in Oxygen led to: The breakdown of the chemicals in the ‘chemical soup’ to carbon dioxide and oxidised sediments The formation of the ozone layer, which blocked out UV and stopped the production of more of the ‘soupy’ molecules After about 2 billion years of prokaryote life (2 billion years ago) there was an Earth changing event: a form of chlorophyll appeared in bacteria that allowed oxygenic photosynthesis

23. D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes Endosymbiosis is the theory that chloroplasts and mitochondria were once free- living prokaryotes that were engulfed by larger prokaryotes and survived to evolve into the modern organelles Evidence in support: 1.Mitochondria and Chloroplasts have their own DNA that is more like bacterial DNA than what is found in the nucleus 2.The structure and biochemistry of chloroplasts is similar to cyanobacteria 3.New organelles are made by a process that resembles binary fission 4.Both organelles have a double membrane which resembles the structure of prokaryotic cells 5.Their ribosomes resemble those of bacteria (70S) 6.DNA analysis suggests that some DNA in plant nuclei was previously in the chloroplast 7.Some proteins coded for in the nucleus are transported to the organelles. The organelles have lost the DNA to make it themselves. http://www.youtube.com/watch?v=q71DWYJD-dI

24. http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_endosymbiosis.html

25. Further information: http://www.youtube.com/watch?v=DE4CPmTH3xg http://exploringorigins.org/timeline.html