NSCI 314LIFE IN THE COSMOS7 - The Origin and Evolution of Life on Earth Dr. Karen KolehmainenDepartment of Physics, CSUSBhttp://physics.csusb.edu/~karen/WHERE DID LIFE BEGIN?MAYBE LIFE WAS DELIVERED TO EARTH FROM AN EXTRATERRESTRIAL SOURCE, AS OPPOSED TO HAVING ORIGINATED HERE (“PANSPERMIA”).–UNLIKELY, ALTHOUGH SIMPLE ORGANIC MOLECULES MAY HAVE BEEN DELIVERED TO EARTH VIA COMETARY IMPACTSPROBABLY NOT ON DRY LAND–IMPACTS AND/OR OTHER ENVIRONMENTAL HAZARDS WOULD MOST LIKELY HAVE WIPED IT OUT–HARD FOR MOLECULES TO REACT ENOUGH TO PRODUCE LONG POLYMERS UNLESS DISSOLVED IN A LIQUIDPOSSIBILITIES:–OCEANS NEAR HYDROTHERMAL VENTS –SMALL POOLS OF WATER (TIDEPOOLS?)–HOT SPRINGS–INSIDE ROCKSDID LIFE BEGIN AT HYDROTHERMAL VENTS?PRO:–ENVIRONMENT NOT AFFECTED MUCH BY BOMBARDMENT, UV RADIATION, AND OTHER ENVIRONMENTAL HAZARDS ON EARLY EARTH–SOME DNA EVIDENCE IS CONSISTENT WITH THISCON:–VENT LIFETIME SHORT (FEW CENTURIES)–MATERIALS QUICKLY DILUTED IN SEAWATER–MAYBE TOO HOT –SOME DNA EVIDENCE IS CONSISTENT WITH THISBOTTOM LINE: WE DON’T KNOWDID LIFE BEGIN IN SMALL POOLS OF WATER (MAYBE TIDEPOOLS)?WATER DISSOLVES MOLECULES SO THAT THEY CAN MOVE AROUND AND INTERACT MORE EASILY TO FORM LARGE MOLECULES.WATER PROVIDES SOME PROTECTION FROM ENVIRONMENTAL HAZARDS (BUT NOT AS MUCH AS VENT ENVIRONMENT DOES).IN A SMALL BODY OF WATER, CHEMICALS CAN BECOME MORE CONCENTRATED THAN IN A LARGE BODY OF WATER LIKE AN OCEAN.TIDES OCCASIONALLY BRING IN NEW MATERIALS INTO TIDEPOOLS.SOLID SUBSTRATE AT THE BOTTOM OF THE POOL COULD AID IN LINING UP MONOMERS TO FORM POLYMERS, AND SELECTING ONE HANDEDNESS (ISOMER) OF MOLECULES.MILLER-UREY EXPERIMENTSATTEMPTS TO CREATE LIFE IN THE LABORATORYPROVIDE A MIXTURE OF GASES SIMILAR TO THAT IN THE EARLY ATMOSPHEREPROVIDE WATER TO SIMULATE OCEANS OR POOLSPROVIDE A SOURCE OF ENERGYWAIT AND SEE WHAT HAPPENSWATERGASES:•H2O (WATER VAPOR)•CO2(CARBON DIOXIDE)•N2(NITROGEN)•H2(HYDROGEN)•CH4(METHANE)•NH3(AMMONIA)ENERGY:•HEAT•ELECTRIC SPARK (LIGHTNING)•ULTRAVIOLET LIGHTTIME (WAIT A FEW DAYS TO WEEKS)INGREDIENTS FOR MILLER-UREY EXPERIMENTSRESULTSMANY ORGANIC MOLECULES ARE PRODUCED, INCLUDING:SUGARS (INCLUDING RIBOSE)FATS OR LIPIDSAMINO ACIDS (50% L AND 50% D)GENETIC BASESNOTE: IF OXYGEN IS PRESENT, THESE MOLECULES ARE NOT FORMED!! (IF OXYGEN IS PRESENT, EVERYTHING CO2 & H2O)LIMITATIONSNOT ALL IMPORTANT ORGANIC MOLECULES ARE FORMEDNO ACTUAL LIVING ORGANISMS ARE FORMED WHY? MAYBE BASIC IDEA IS WRONGMAYBE MORE TIME IS NEEDED (MILLIONS OF YEARS, NOT JUST A FEW WEEKS OR MONTHS) – AFTER ALL, LIFE ON EARTH HAD HUNDREDS OF MILLIONS OF YEARS TO GET STARTED!MAYBE SOME KEY INGREDIENT IS MISSINGSOURCES OF SIMPLE ORGANIC MOLECULES ON EARLY EARTHMILLER-UREY TYPE REACTIONS IN–SMALL POOLS OF WATER–OCEANS NEAR HYDROTHERMAL VENTS–OTHER LOCATIONS?DELIVERY VIA COMET AND ASTEROID IMPACTSTHESE PROBABLY ALL PLAYED A ROLEBUT THIS ISN’T LIFE YET!WHAT HAPPENED NEXT?POLYMERIZATIONHOW DID SIMPLE ORGANIC MOLECULES (MONOMERS) JOIN UP TO MAKE LONG POLYMERS?IF IMMERSED IN A LIQUID, THEY CAN MOVE AROUND AND COMBINE MORE EASILY.THEY WILL BE MORE LIKELY TO ENCOUNTER EACH OTHER AND COMBINE IF THEY ARE CONCENTRATED, AS WOULD HAPPEN IN A SMALL POOL.THEY MAY HAVE ORGANIZED THEMSELVES ON SURFACES OF CRYSTALS OR CLAY. –THIS REQUIRES A SOLID SUBSTRATE, SUCH AS THE BOTTOM OF A SMALL POOL OF WATER.–THE SHAPE OF THE SURFACE MAY HELP THE MONOMERS LINE UP PROPERLY. –THIS MAY HAVE ALSO SELECTED ONE HANDEDNESS.–EXPERIMENTS HAVE SHOWN THAT THEY CAN LINE UP PROPERLY ON CERTAIN SOLID SUBSTRATES.PROTEINS, DNA, AND RNADNA AND RNA CAN REPLICATE THEMSELVES (AN IMPORTANT CHARACTERISTIC OF LIFE).IN MODERN LIVING ORGANISMS, DNA AND PROTEINS INTERACT IN IMPORTANT WAYS.–INSTRUCTIONS FOR CONSTRUCTING PROTEINS ARE CARRIED IN DNA.–PROTEINS ARE IMPORTANT IN CONSTRUCTING DNA. (SOME ARE NEEDED FOR DNA REPLICATION).“CHICKEN AND EGG” PROBLEM: WHICH CAME FIRST?POSSIBLE SOLUTION: RNA MAY HAVE PRECEDED DNA AS GENETIC MATERIAL IN EARLIEST LIFE FORMS (LIKE IN SOME MODERN VIRUSES). RNA CAN FILL THE ROLE OF PROTEINS AS WELL AS THAT OF DNA.ORIGIN OF CELLSALL LIFE ON EARTH OF MADE OF CELLS.A CELL IS SEPARATED FROM ITS ENVIRONMENT BY A MEMBRANE.EXPERIMENTS SUGGEST HOW CELLS MAY HAVE ORIGINATED. EXPERIMENTS HAVE SHOWN THAT ORGANIC POLYMERS DISSOLVED IN WATER CAN EASILY GROUP TOGETHER INTO DROPLETS, AND MEMBRANES CAN FORM AROUND THE DROPLETS. WHICH CAME FIRST - CELLS OR SELF-REPLICATION? WE DON’T KNOW!–IF CELLS FORMED FIRST, THEY COULD HAVE CONCENTRATED THE POLYMERS THAT FORMED INSIDE.–IF SELF-REPLICATING POLYMERS FORMED FIRST, THEY MAY HAVE USED A SMALL POOL AS A “HOST” BEFORE CELLS EXISTED (SIMILAR TO THE WAY MODERN VIRUSES USE A HOST CELL FOR REPLICATION) .MUTATIONSCHANGES IN THE SEQUENCE OF BASES IN DNA DUE TO MISTAKES IN DNA REPLICATION.THESE OCCUR EITHER RANDOMLY (LESS THAN ONCE PER BILLION BASES), OR BECAUSE OF EXPOSURE TO HIGH ENERGY PHOTONS (ULTRAVIOLET, X-RAYS, OR GAMMA RAYS), OTHER HIGH ENERGY PARTICLES, OR CERTAIN CHEMICALS.WHAT IS THE EFFECT OF A MUTATION? REMEMBER THAT THE DNA IS PART OF A GENE THAT CODES FOR A PARTICULAR PROTEIN. WHAT IS THE EFFECT ON THE PROTEIN? –SOMETIMES THERE IS NO EFFECT ON THE PROTEIN (BECAUSE OF THE REDUNDANCY IN THE GENETIC CODE).–SOMETIMES THERE IS A CHANGE IN SEQUENCE OF AMINO ACIDS IN THE PROTEIN, OFTEN CHANGING ITS FUNCTION.•ADDITIONALLY, SOMETIMES THERE IS A CHANGE IN THE WAY THE PROTEIN IS FOLDED. (THIS IS CAUSED BY A CHANGE IN THE AMINO ACID SEQUENCE.)MUTATIONSSOME MUTATIONS HAVE IMPORTANT EFFECTS, AND OTHERS DO NOT.OF THOSE THAT DO HAVE IMPORTANT EFFECTS, MOST RESULT IN CHANGES ARE HARMFUL TO THE ORGANISM, BUT A FEW ARE BENEFICIAL TO THE ORGANISM.FOR MUTATIONS THAT HAPPEN IN MOST CELLS OF A MULTICELLULAR ORGANISM, THAT ORGANISM ITSELF MAY BE AFFECTED (e.g., CANCER), BUT THE CHANGE IS NOT PASSED ON TO THE ORGANISM’S OFFSPRING.IF A MUTATION HAPPENS IN AN EGG OR SPERM CELL (OR IN A SINGLE-CELLED ORGANISM), THEN IT IS PASSED ON TO THE ORGANISM’S SUBSEQUENT OFFSPRING.EVOLUTIONTHE RESULT OF MUTATIONS THAT HAVE BEEN PASSED ALONG TO OFFSPRINGNATURAL SELECTION: –IF THE MUTATION IS HARMFUL, THE ORGANISM HAS REDUCED REPRODUCTIVE SUCCESS. THE MUTATION IS “WEEDED OUT” OF THE POPULATION.–IF THE MUTATION IS BENEFICIAL, THE ORGANISM HAS GREATER REPRODUCTIVE SUCCESS. THE MUTATION IS
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