Modeling Chemical Evolution Biology

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

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.

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.

Results of the Experiment Two percent of the carbon had formed amino acids that 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. http://www.youtube.com/watch?v=mUgOPYhXSxY&safety_mode=true&persist_safety_mode=1&safe=active

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) http://www.pbs.org/wgbh/nova/evolution/origins-life.html

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

1-Chemical Evolution Inorganic Molecules Organic 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

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

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.

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)

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

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

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

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