Modeling Chemical Evolution

1. Modeling Chemical Evolution Biology

3. Miller-Urey Experiment • Stanley Miller & Harold Urey • University of Chicago • 1952 • Simulated the early conditions thought to be on Earth… what were they again???

4. The Experiment • The experiment used water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2). • The chemicals were all sealed inside a sterile array of glass tubes and flasks connected in a loop, with one flask half-full of liquid water and another flask containing a pair of electrodes. • The liquid water was heated to induce evaporation. • Sparks were fired between the electrodes to simulate lightning through the atmosphere and water vapor.

6. The Experiment Continued… • The “atmosphere” was cooled again so that the water could condense and trickle back into the first flask in a continuous cycle. • At the end of one week of continuous operation, Miller and Urey observed that as much as 10–15% of the carbon within the system was now in the form of organic compounds.

7. Results of the Experiment • Two percent of the carbon had formed amino acidsthat are used to make proteins in living cells, with glycine as the most abundant. • Sugars, lipids, and some of the building blocks for nucleic acids were also formed. • Since this experiment, other scientists have repeated and extended the research. As a result, all 20 amino acids, sugars, lipids, nucleotides, and ATP have been produced.

8. Why does all of this matter? • Two things must have been present before life could form… 1 - Simple organic molecules such as amino acids & nucleotides (ATGCU) 2 - Complex organic molecules such as proteins & nucleic acids (DNA,RNA)

9. Current Scientific Theory about the Origin of the First Life Forms 4 Step Process: 1 - Chemical evolution 2 - Polymerization 3 - Microsphere formation 4 - Protocell & Prokaryotic cell formation

10. 1-Chemical Evolution • Inorganic Molecules Water - H2O Methane - CH4 Ammonia - NH3 Hydrogen gas - H2 • Organic Molecules Amino acids (only 20) glycine, alanine, serine… Nucleotides (only 5) adenine, thymine, cytosine, guanine, uracil

11. 2 - POLYMERIZATION • Process of joining 2 small organic molecules (monomers) into larger more complex organic molecules (polymers)

12. 3 - MICROSPHERES • Scientists believe that long chains of complex organic molecules eventually formed a circle around a water droplet. • This is called a microsphere & is believed to have been the precursor to the cell membrane.

13. 4 - PROTOCELLS & PROKARYOTES • Once microspheres formed, it is believed that small chains of nucleic acids (DNA or RNA) became trapped in the sphere creating what scientists call a protocell. • Scientists believe that this eventually developed into a prokaryote (simplest cell type - no nucleus & no organelles)

14. Characteristics of 1st Life? • Single celled • Prokaryotic - no nucleus or organelles • Chemotrophic - fed off chemicals (sulfur, ammonia, methane, etc.) • Anaerobic - lived without free oxygen

16. Alanine-the “radical” can be any atom or molecule

17. Analysis Questions from Lab • 1 – What 2 groups are identical in all amino acids?  • *Amine Group & Carboxlyic Acid Group • 2 – What is a “radical” and why are they important? • remaining bonding site on central C (open area) • determines amino acid to be formed • 3 – What 2 products are produced during the formation of a peptide bond? • *Protein & Water

18. 4 – Arrange the following terms in order of smallest to greatest in size: amino acid, carboxylic acid group, peptide, atom, polypeptide  • atom, carboxylic acid group, amino acid, peptide, polypeptide • 5 – If fifty amino acids are linked in a row, how many peptide bonds are created AND between which two parts of the amino acids does each of these bonds form? • 49 peptide bonds; carboxyl & amine group