N. Bishop

Part II: Replication First (Gene First) or RNA World Hypothesis CLAIM: The first molecule of life was RNA which can both store information and has catalytic ability to copy itself. N. Bishop

TIMELINE Building blocks of RNA form and assemble into nucleotides RNA nucleotides form polymers Some RNAs are catalytic – can make copies of themselves RNAs attract amino acids – serve as template for polypeptides Protein favors RNA survival – later surrounded by membrane Later DNA stores info, proteins take over as catalysts N. Bishop

Part II: Metabolism Hypothesis CLAIM: Life began as interlocked networks of chemical reactions (metabolism) and became more complex over time. N. Bishop

TIMELINE (Iron-Sulfur World Hypothesis) H2S from hydro- thermal vents transfers energy by donating e- Iron compounds become catalyst when they receive e - Iron compounds hold & donate e- to carbon compounds Self-sustaining network of chemical reactions forms Chemical network becomes enclosed in membranes or iron-sulfur “bubble” N. Bishop

Part III: SUPPORT for Replication First Building blocks of RNA form and assemble into nucleotides 1.Such chemical reactions could have occured on early Earth 2.These chemical reactions occur in space 3.Nucleotides can form without creation of building blocks (sugar, base, phosphate) N. Bishop

Part III: SUPPORT for Replication First RNA nucleotides form polymers 1.Clay can attract nucleotides and act as catalyst for forming polymers 2.Polymers can form on frozen sea ice 3.Polymers can form near hot springs N. Bishop

Part III: SUPPORT for Replication First Some RNAs are catalytic – can make copies of themselves 1.Catalytic RNA exists – ribozymes 2.We are just beginning to discover all the reactions that RNAs are involved in! N. Bishop

Part III: SUPPORT for Replication First RNAs attract amino acids – serve as template for polypeptides 1.Current cells can do this – tRNA and ribosomal RNA 2.RNAs created in lab can do this N. Bishop

Part III: EVIDENCE AGAINST Replication First 1.How could RNAs form in the presence of so many building blocks? 2.RNA nucleotides can link together more than one way. 3.Replication by ribozymes is slow and has a high error rate. 4.RNA is unstable. Could it persist long enough for life to begin? N. Bishop

Part III: SUPPORT for Metabolism First 1.Experiments have produced a variety of organic molecules using metal as a catalyst. 2.Some proteins in our cells do require the presence of metal atoms to carry out catalysis. 3.Pores in hydrothermal vents provide containers for concentrating chemicals and for maintaining temperatures suitable for chemical reactions 4.Cells escaping iron-sulfide bubbles at different times could have chemically different membranes like current bacteria and archaea N. Bishop

Part III: SUPPORT for Metabolism First 5. Thermophilic bacteria that thrive on sulfur, methane and hydrogen are at the root of the evolutionary tree. N. Bishop

Part III: EVIDENCE AGAINST Metabolism First 1.Iron-sulfur catalyst cannot catalyze CO 2 (expected in early ocean) 2.Simulations indicate iron-sulfur catalyst very slow 3.Electron transfer near hydrothermal vents too slow N. Bishop

WHY ARE THESE HYPOTHESES NOT THEORIES? AS USED IN SCIENCE: Theory - an explanation of some aspect of the natural world that has been repeatedly tested and confirmed through observation and experiment. Hypothesis – a testable explanation made on the basis of limited evidence as a starting point for further investigation N. Bishop

MISCONCEPTIONS! “Evolution is a theory about the origin of life.” Evolutionary theory deals mainly with how life changed after its origin NOT how life started. Most evolutionary studies are focuses on how life branched and diversified after life started. However, science does try to investigate how life started. N. Bishop