Lecture 3 Notes - Cell Origins
Lecture 3 Notes - Cell Origins BIL 255
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This 5 page Class Notes was uploaded by Elizabeth Mompoint on Tuesday September 22, 2015. The Class Notes belongs to BIL 255 at University of Miami taught by Dr. Mallery in Fall 2015. Since its upload, it has received 22 views. For similar materials see Cellular & Molecular Biology in Biology at University of Miami.
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Date Created: 09/22/15
Cell and Molecular Biology Lecture 3 0 Origin of Cells Most experimental evidence favors a chemical evolutionary origin of life Earth formed 46 billion years ago between 45 to 40 bya asteroids bombard amp sterilize planet39s surface then by 35 bya first fossil evidence of microscopic life is present stromatolites Paleontologists study the forms of life in past geological periods by analyzing fossils through radiocarbon dating 0 14C has a halflife of 5730 years There are four views on the origin of life 1 Supernatural Creation based upon faith in which a supernatural being suspended the Laws of Chemistry and Physics to create life 2 Cosmetologists suggest that life is a unique accident and that its establishment was a singular event of unnatural possibility that is not likely to ever occur again 3 The third view is that life or the molecular components of life may have an original extra terrestrial origin and arose from a Panspermia 4 Chemical Evolution built upon the idea that all of the molecules which we can easily find in known living cells are made from the same small number of chemically reactive functional groups OH C02 NH2 COOH PO4 SH There are five steps in the sequence of events in the progression of chemical evolution from molecule to living cell First is the abiotic svnthesis of small organic molecules Second is the autocatalvtic assemblv of Dolvmers from abiotic monomers Third is the establishment of a hereditary information blueprint Fourth is the linking of selfreplicating RNA molecules to the formation of simple polypeptides Fifth is the encapsulation of the chemical s replicative processes into membranes a Coacervates are aggregations of macromolecules with catalytic activity in droplets with fat like boundary interfaces b A protobiont is a coacervate with specific encapsulated enzymatic properties Originoflife research has followed 2 approaches 1 A metabolism first approach in which chemical cycles may have led to the synthesis of organic molecules based upon idea of speculative prebiotic chemistry 2 A genetics first approach which favors the formation of some sort of replicating information molecule as being necessary prerequisite for life U PP PN 0 3 possible sources for first abiotically produced metabolic bioorganic molecules Molecules formed from a chemically reactive soup in the early oceans of primitive Earth 0 1953 Miller amp Urey achieve abiotic synthesis of organics in lab experiments at U Chicago I Passed sparks in brew of CH4 NH3 H2 amp H2O vapor to make HCN amp formaldehyde then amino acids nucleotides amp sugars 7 r m 0 2007 Repeat of MillerUrey experiments by Sam Bada who discovers 1953 samples m smlnm Molecules formed in deep dwelling hydrothermal vents mm SEW O 2007 Vents are full of organically rich 0 O Black Smokers chlirners of deposlts 01 FEB also White Smokers deposits 01f Ba Ba Si molecules amp constitute an ecosystem of bacterial life amp life worms crabs etc amp even a LUCA 2003 Huber amp Wachtershauser propose a beginning for metabolism in an Iron Sulfur World I Key organic molecules may have originated at vents with superheated water 300 C I H2S amp Fe gt pyrite FeS2 amp H2 and favors reduction of N2 to NH3 amp possible amino acids Speculation Chemosynthesis may have helped life originate in ventlike regions producing first biomolecules amp metabolic reactions 2012 Vents vs warm little ponds a Deepsea vnnl hypothesls b A daenssea vanl cummum v Astrobiological origin for biomolecules O O O 0 Early earth constantly bombarded by meteorites was a sterile habitat until space debris deposited organics on newly formed Earth Comets may be responsible for much of Earth s water Rosetta Spacecraft Asteroids contain organic molecules nucleobases quinones COOH s amines amp amides Extrasolar system gas planet shown to have organics spectrums find CO2 CH4 amp H20 0 Experimental Approaches used in Origin of Life Research The three above Build an artificial model molecular replicative system 0 Argues for the emergence of RNA molecular replication as both an informationcarrier molecule and a catalytic molecule as the important 1st step Evolution of an RNA world 1st proposed by Walter Gilbert in 1986 1989 Sidney Altman amp Tom Cech received Nobel Prize for demonstrating that RNA molecules ribozymes have catalytic activity A long standing weakness of the RNAworld hypothesis has been the inability to spontaneously generate the RNAs molecule s nucleotides from the basic ingredients presumed to be available on the prebiotic Earth Build molecularly active vesiclized quotprotocellsquot O Proteinoids aggregates of abiotically made organic molecules surrounded by a membrane I Molecules in solution are randomized amp unable to maintain an organized state order yet compartments allow concentration and increased reactivity Sidney W Fox conducted analyses of the first moon rock samples amp produced proteinoids amp microspheres by dropping amino acid solutions on hot lava rock or clay Experimental systems include coacervates proteinoid microspheres amp liposomes I Coacervate droplets formed by polypeptides polysaccharides nucleic acids ampor lipids have tough skin of water molecules held by hydrophobicity with osmotic capability I Proteinoids abiotic protein polymers can form microspheres 12um dia I Liposomes are microscopic spherical vesicles that form spontaneously when phospholipids are hydrated Hollow sphere of phospholipid Phospholipid tilled with water bilaver Skin oi water r r quot 39 b lLiposolmee a cga ewateg l l ILLm Solidi droplet of protein and Emmi dram Figure 184 Protobionts and their lifelike functions Primitive celllike structures such as coacervates and liposomes could have given rise to living cells a An electron micrograph and illustration of liposomes iEach liposome is made of a phoslplholipid bilayer surrounding an ego eous compartment Protobionts 8 their lifelike functions Primitive celllike structures such as coacervates might have given rise to primitive cells Above is a micrograph of coacervates which are droplets of protein and carbohydrates surrounded by a skin ofwater 0 A Genetic experimental approach Via Synthetic Biology and Artificial Cell Research The ultimate challenge of CMB may be to construct an artificial organism that can reproduce amp evolve Synthetic Biology uses a bottomup approach it is the construction of fully functional cells or parts from scratch Some experimental examples of synthetic biology accomplished With Viri 0 Synthetic Polio Virus Eckard Wimmer used the polio Virus Widely known genetic sequence to synthesize a Virus from shelf chemicals 0 Phi X174 Virus was artificially synthesized in Nov 2003 by Craig Venter and colleagues using synthetic DNA sequences ordered from a biotechnology company amp a technique called polymerase cycle 0 The 1918 Spanish Flu Virus is Reconstructed October 2005 by Jeffery K Taubenberger Knockout cells looking for a minimalist essential genome required to make a cell leads to synthesis of an artificial functional genome 0 Of the 482 proteinencoding genes only about 382 of them are essential to life 1 Prebiotic Primordial Soup a Emiliaquot 3 394 I In affirm it A Hamming mlmtin gamer 7quot r wl WHHWJ 2 Hydrothermal Vents 3 MeteoriteComets Asteroids Mimicking the primordial conditions of Earth in 1953 Miller amp Urey abiotically created amino acids by exposing a mix of volcanic gases ammonia methane hydrogen sulfide CO2 to a lightninglike electrical spark Using modern analytical procedures Jeff Bada amp Eric Parker analyzed Miler samples years later and found 23 amino acids 4 amines and several other organics suggesting that volcanic eruptions amp lightning may have synthesized a variety of prebiotic organic molecules Submarine hydrothermal vents spewing key hydrogenrich molecules along with mineral catalysts may have provided the first prebiotic molecular system Carbonyl sulfide a vents chemical and added minerals has been used in the lab to form peptides from amino acids Carbon rich meteorites known as carbonaceous chondrites such as the Murchison Meteorite ALH84001 contain amino acids as glycine alanine and glutamic acid Alkanes also occur Measured purine and pyrimidine compounds are indigenous to meteorites Comets also contain lots of organics Many organic compounds which are common to life on Earth were already present in the early solar system and may have played a role in life39s origins on Earth Minerals may have allowed the first molecules of life to react with each other in clays Their surfaces may have allowed them to concentrate and to even organize them into polymeric patterns like genes do now Alex CairnsSmith suggested that mineral crystals in clay may have allowed organics to organize in complex patterns Ice hundreds of feet thick might have covered the Earth39s oceans 3 billion years ago and could have protected the fragile organic compounds in the waters below from UV light and cosmic ray impact The cold could have helped these molecules survive longer allowing key reactions to happen 6 RNA World RNA can store information like DNA has catalytic enzymelike activity and functioned to help create DNA and proteins and therefore may have supported precellular life being a major step in the evolution of cellular life Selfreplicating molecular systems may have originated with RNA This idea being a genefirst model of life 7 39Protobionts39 F39Eilll i39iJELE E39FLPEF EgaEEJ39 TETE Fl J39squotivquot EARLquot3 31EMHHJiaE39EIl1iE n ti g itar3Eit rlam 0f MetabOIism may haVe begun incite35515 a smaller molecules interacting with each other in 39 tr 3 cycles of reactions These might have been simple quotmembranequot capsules Over time more complex m molecules that performed these reactions better tl ii w t than the smaller one could have evolved a 1 quotmetabolismfirstquot model of life39s replicating 7 finaliseMutant SYStemS i L39Ii iiUi L i E39I i H I 1 lil H Maybe life did not originate on Earth at all but was brought her from elsewhere in space Earth is routinely bombarded by space debris and maybe microbes are capable of surviving space travel Life may have hitchhiked on comets from other star systems but then how did Life begin elsewhere in space
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