A 2.1_Originofcells.pptx

1.5 Origin of cells Essential idea: There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today. In the background you can see Late Mesoproterozoic and Neoproterozoic eukaryotic fossils images of cells. We know from such evidence that cells have always wo...

1.5 Origin of cells Essential idea: There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today. In the background you can see Late Mesoproterozoic and Neoproterozoic eukaryotic fossils images of cells. We know from such evidence that cells have always worked using the same basic principles. http://rstb.royalsocietypublishing.org/content/361/1470/1023/F3.larg Understandings, Applications and Skills 1.5.A1 Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth. Use the tutorials to learn about Pasteur’s experiment. http://www.sumanasinc.com/webcontent/animations/conte nt/scientificmethod.html Repeat Pasteur’s experiment and see the results for yourself. https://youtu.be/Xc-hHhDID9A http://bcs.whfreeman.com/webpub/biology/sadavalife9e/animated% 20tutorials/life9e_0401_pasteurs_exp.swf http://biologyjunction.com/pasteur_experi ment.htm Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth. Louis Pasteur designed an experiment to test whether sterile nutrient broth could spontaneously generate microbial life. Method: • Two experiments were setup • In both, Pasteur added nutrient broth to flasks and bent the necks of the flasks into S shapes • Each flask was then heated to boil the broth in order than all existing microbes were killed. • After the broth had been sterilized, Pasteur broke off the swan necks from the flasks in Experiment 1, exposing the nutrient broth within them to air from above. • The flasks in Experiment 2 were left alone. Results: • The broth in experiment 1 turned cloudy whilst the broth in experiment 2 remained clear. • This indicates that microbe growth only occurred in Conclusion: Pasteur experiment 1. rejected the hypothesis of spontaneous generation as for growth of microbes to occur a source of contamination was needed. Q – was Pasteur correct, could spontaneous generation of life never http://bcs.whfreeman.com/thelifewire/content/chp03/0302003. occur? According to the cell theory, living organisms are composed of cells. Cell theory states that: We will slide cove pres r ne xt enta tion A 2. 2 • All living things are composed of cells (or cell products) • The cell is the smallest unit of life • Cells only arise from pre-existing cells Source: Cells can only be formed by division of pre-existing cells. Cells can only be formed by division of pre-existing cells: • Cells multiply through division • Mitosis results in genetically identical diploid daughter cells • Meiosis generates haploid gametes (sex cells) 4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC) Cells can only be formed by division of pre-existing cells. What evidence do we have (other than Pasteur’s experiments) to support this theory? 4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC) Cells can only be formed by division of pre-existing cells. 1. Cells are highly complex structures and no mechanism has been found for producing cells from simpler subunits. http://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Eukaryotic_Cell_%28animal%29.jpg/1024px-Eukaryotic_Cell_%28 Cells can only be formed by division of pre-existing cells. 2. All known examples of growth be it of a tissue, an organism or a population, are all a result of cell division. http://upload.wikimedia.org/wikipedia/commons/thumb/d/d3/Onion_root_mitosis.jpg/749px-Onion_roo Cells can only be formed by division of pre-existing cells. 3. Viruses are produced from simpler subunits, but they do not consist of cells, and they can only be produced inside the host cells that they have infected. http://upload.wikimedia.org/wikipedia/commons/3/3a/Influenza_virus_particle_color.jpg Cells can only be formed by division of pre-existing cells. 4. Genetic code is universal each of the 64 codons (a codon is a combination of 3 DNA bases) produces the same amino acid in translation, regardless of the The logical[D deduction organism 1.1]*. is that all cells have arisen as the result of cell division from a single common ancestor. * There are some minor variations that are likely to have accrued since the common origin of life on Earth, but these are rare and most of the genetic code is universal most of the time. http://www.slideshare.net/gurustip/protein-synthesis-35-transcription The first cells must have arisen from non-living material. 1. Non-living synthesis of simple organic molecules, e.g. sugars and amino acids 2. Assembly of these organic molecules into polymers 3. Formation of polymers that can self-replicate (enabling inheritance) 4. Formation of membranes to package the organic molecules http://exploringorigins.org/resources.html If we accept that there were times in the history of the Earth when cells did not exist then it is an obvious point that ‘The first cells must have arisen from non-living material’. The only other possible explanation is that life, in the form of cells, was transported here from elsewhere in the universe. As illustrated above, it is extremely difficult (and given our level of technology currently impossible), to generate cells from anything but other cells. So how did the first cells arise? Some of the key problems are: The first cells must have arisen from non-living material. Earth’s atmosphere was ‘reducing’ in the early days. It did not contain oxygen gas until after plants started photosynthesising Can you identify these molecules? All molecules public domain from Wikimedia Commons, Background image The first cells must have arisen from non-living material. 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 Ammonia Hydrogen sulfide The gases came from abundant volcanic activity All molecules public domain from Wikimedia Commons, Background image The first cells must have arisen from non-living material. These monomers mixed in the ‘primeval 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/6636 The first cells must have arisen from non-living material. After a week they found: Thirteen of the twenty naturally occurring amino acids Around 15% of the carbon was now in organic compounds The first cells must have arisen from non-living material. 1. Non-living synthesis of simple organic molecules: Miller and Urey recreated the conditions of pre-biotic Earth in a closed system. • These conditions included a reducing atmosphere (low oxygen), high radiation levels, high temperatures and electrical storms • Water was boiled to form vapour • and then was mixed with methane, ammonia and hydrogen • The mixture of gases was exposed to an electrical discharge (sparks) to simulate lightning • Carny The mixture was then allowed to cool and after one week was found to contain some simple amino acids and complex oily hydrocarbons Based on these findings, it was concluded that under the hypothesised conditions of prebiotic Earth, organic molecules could be formed The first cells must have arisen from non-living material. 2. Assembly of these organic molecules into polymers: Miller and Urey’s experiments allowed for the formation of amino acids, but the conditions used also tended to hydrolyse bonds preventing polymers forming. Deep-sea thermal vents • Fissures in a planet's surface from which geothermally heated water issues. Vents are commonly found near in volcanically active areas) • Along with heat energy the Vents issue a ready supply of reduced inorganic chemicals • Vents provide the right conditions and chemicals to allow organic polymers to arise. http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Blacksmoker_in_Atlantic_Ocean.jpg/220px-Blacksmoker_in_A The first cells must have arisen from non-living material. • DNA though very stable and effective at storing information is not able to self-replicate – enzymes are required • However RNA can both store information and self-replicate - it can catalyse the formation of copies of itself. • In ribosomes RNA is found in the catalytic site and plays a role in peptide bond formation For more detail research the RNA World Hypothesis http://exploringorigins.org/resources.html 3. Formation of polymers that can self-replicate (enabling inheritance) The first cells must have arisen from non-living material. 4. Formation of membranes to package the organic molecules Experiments have shown that phospholipids natural assemble into bilayers, if conditions are correct. Formation of the bilayer creates an isolated internal environment. The formation of an internal environment means that optimal conditions, e.g. for replication or catalysis can be maintained. http://upload.wikimedia.org/wikipedia/commons/thumb/0/01/Liposome_scheme-en.svg/220px-Liposome_scheme-en.svg.pn The origin of eukaryotic cells can be explained by the endosymbiotic theory. Endosymbiotic theory explains the existence of several organelles of eukaryotes. The theory states that the organelles (e.g. mitochondria and chloroplasts) originated as symbioses between separate single-celled organisms, Use the video and/or the tutorial to understand how this occurred. http://youtu.be/q71DWYJ D-dI https://highered.mheducation.com/sites/9834092339/student_view0/chapter4/animation_-_endos The origin of eukaryotic cells can be explained by the endosymbiotic theory. Development of the Nucleus • A prokaryote grows in size and develops folds in it’s membrane to maintain an efficient SA:Vol • The infoldings are pinched off forming an internal membrane • The nucleoid region is enclosed in the internal membrane and hence becomes the nucleus http://ib.bioninja.com.au/options/option-d-evolution-2/d1-origins-of-life-on-earth.html The origin of eukaryotic cells can be explained by the endosymbiotic theory. * An endosymbiont is a cell which lives inside another cell with mutual benefit The development of chloroplasts would be a very similar process Development of Mitochondria except the benefit to the cell would be glucose/starch instead of ATP • An aerobic proteobacterium enters a larger anaerobic prokaryote (possibly as prey or a parasite) • It survives digestion to become a valuable endosymbiont* • The aerobic proteobacterium provides a rich source of ATP to it’s host enabling it to out-compete other anaerobic prokaryotes • As the host cell grows and divides so does the aerobic proteobacterium therefore subsequent generations automatically contain aerobic proteobacterium. • The aerobic proteobacterium evolves and is assimilated to become a http://ib.bioninja.com.au/options/option-d-evolution-2/d1-origins-of-life-on-earth.html The origin of eukaryotic cells can be explained by the endosymbiotic theory. The evidence supporting the endosymbiotic theory for mitochondria and chloroplasts: • They have their own DNA (which is naked and circular) • They have ribosomes that are similar to prokaryotes (70S) • They have a double membrane and the inner membrane has proteins similar to prokaryotes • They are roughly the same size as bacteria and are susceptible to the antibiotic chloramphenicol • They transcribe their DNA and use the mRNA to synthesize some of their own proteins. • They can only be produced by division of pre-existing mitochondria and http://sites.roosevelt.edu/mbryson/files/2011/11/endosymbiosis.jpg chloroplasts. Exploring the Origin of Cells: Last Universal Common Ancestor (LUCA) and Evolution at Hydrothermal Vents The Mystery of Life’s Origin The origin of life remains a profound scientific mystery. • How did the first cells come into existence? • LUCA: A key concept in understanding this puzzle. Last Universal Common Ancestor (LUCA) LUCA is the hypothetical singlecelled organism from which all life on Earth descended. Represents the point where the tree of life's branches converge. Shared genetic and biochemical features provide clues about LUCA's characteristics. Unveiling LUCA's Characteristics Genetic evidence suggests LUCA was a prokaryote, lacking a nucleus and organelles. Likely thrived in anaerobic environments with limited oxygen. Possessed basic metabolic pathways for energy production. Calculating the Age of LUCA Estimating LUCA's age is challenging due to the lack of direct evidence. Genetic analysis and molecular clock methods help approximate LUCA's existence around 3.5 to 3.8 billion years ago. Geological and geochemical records provide additional insights into early Earth conditions. Molecular Clocks: use of Cladistics Molecular clocks use genetic mutations to estimate evolutionary time. Accumulation of mutations provides a relative timeline. Helps approximate LUCA's age by comparing genes among different organisms. Evolution at Hydrothermal Vents Extreme environments on the ocean floor with high pressure, temperature, and mineral-rich fluids. Hypothesized as potential sites for life's origin due to the availability of energy and organic molecules. Hydrothermal Vent Ecosystems Chemosynthetic bacteria thrive near hydrothermal vents. These bacteria convert inorganic compounds into organic molecules, serving as a foundation for vent ecosystems. Vent Hypothesis for LUCA's Origin Vent hypothesis suggests life could have originated at hydrothermal vents. Energy-rich compounds released from vents could have supported early life's energy needs. Minerals in vent environments may have acted as catalysts for key biochemical reactions. Evidence Supporting the Vent Hypothesis Similarities between modern extremophiles (organisms living in extreme conditions) and LUCA's hypothetical characteristics. Chemosynthetic pathways found in modern organisms resemble potential early metabolic pathways. LUCA's Legacy LUCA's genetic legacy is reflected in the diversity of life on Earth today. Deciphering LUCA's characteristics provides insights into the early stages of evolution. The search for LUCA helps us understand the unity and diversity of life.