3 What is life?One way to answer this question would be to require certain properties that we associate with living things.Obviously a bad choice. Many living thing do not have legs.For example: It must have legsIt must have metabolismThis sounds much more reasonable.BUT!Unfortunately, there are things that behave just as if they has a ‘living’ metabolism, but these things are not alive.
4 What is life? What can be considered to have metabolism but not life? Fire!Atoms go in, change, and go out. This process is essential for the survival to the phenomenon. The overall phenomenon is constant (i.e. there is a flame) for as long there is food (oxygen, fuel …). There even can be replication (one fire can light another fire).But obviously, we do not consider fire to be alive.
5 What is life? Is there a better way to describe what’s alive? One could look at the properties that are required for a population to evolve by natural selection.MultiplicationHeredityMutationFor individuals of the population, the requirement should be made a bit less strict in that at least the parents fulfill the above requirement (a mule e.g. cannot multiply).
6 What is origin of life?* God? Outer space? a way to envisage the origin or life as a series of simple steps is more satisfactory than a single, massively improbable event….*by definition, the origin of life only happened once and no one was around to see it
7 Stages of prebiotic evolution How did the earth’s crust and atmosphere look like when life originated?Geophysical StageChemical StageBiological StageReasonably well understood.How can the building blocks of life (nucleotides, amino acids) be synthesized?These blocks may (partially) have been different from modern blocks.How did the building blocks organize into living organisms?Poorly understood.
8 Geophysical stage H2O, CO, CO2, N2, H2S and H2 The first atmosphere probably consisted of gaseous hydrogen, nitrogen, carbon monoxide and carbon dioxideGaseous oxygen and water were not thought to be presentWhen the crust cooled the water condensed, rains began, and pools of chemicals began to form
9 Urey-Miller experiment Chemical stagetovacuumpumpboiling watersparkdischargeliquid water in trapwater containingorganic compoundswater dropletswater incondenserelectrodeswater outCH4NH3H2OH2gases1938:Aleksandr Oparin1953:Urey-Miller experimentExperiment by Miller:In a reducing environment, amino acids and bases are easy to synthesize from naturally occurring molecules. The experiments fail in a neutral or oxygen-rich atmosphere.
10 Chemical stage Multiple variations of the study (e.g., atmosphere) 20+ amino acids, sugars, bases for DNA and RNA, ATP, etc.Significance: scenario for the abiotic formation of key carbon polymers (macromolecules)Probable environmentsDeep sea ventsTidal pools (role of repeated evaporation and concentration – “evapoconcentration”)Chemical events leading to an “RNA World”
11 a word about RNA diversity and catalysis… Biological stageSome common biopolymers that could have participated in the formation of early life: Proteins: amino acid diversity, catalysis DNA: stability and storage RNA: diversity, storage, and catalysis!a word about RNA diversity and catalysis…
13 a “natural” RNA enzymeIn 1982, Tom Cech et al discovered that an intron within a pre-rRNA from Tetrahymena thermophila can catalyze its own cleavage (called self-splicing) to form the mature rRNA product.
15 RNA-based RNA polymerase Why are ribozymes important for an RNA world hypothesis?RNA-based RNA polymeraseHypothetical moleculecompletely self-replicating+ nucleotides
16 reconstructing evolution:making RNA enzymes SELEX: Systematic evolution of ligands by exponential amplificationThis technique makes useof large populations ofrandom RNA or DNAsequences as the rawmaterial for the selectionof rare functional molecules.
17 RNA enzymes from selex experiments These types of enzymes have been made!Limited polymerizationRNA ligasesRNA cappingRNA phosphorylationRNA cleavagePeptide bond formationAmide bond formationCan a high school lab do selex experiments? YES!
18 a minimal ribo-organism Will this be made one day?Bartel and Unrau, TCB 1999
19 overview and conclusions livingcellsmembrane-bound proto-cellsself-replicating system enclosed in aselectively permeable, protective lipid sphereDNARNAenzymes andother proteinsThe “Central Dogma”formation ofprotein–RNA systems,evolution of DNAlipid spheresspontaneous formation of lipids,carbohydrates, amino acids, proteins,nucleotides under abiotic conditions