Biology

Miller-Urey ExperimentStanley Miller & Harold UreyUniversity of Chicago1952Simulated 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 ExperimentTwo 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.

Why does all of this matter?Two things must have been present

before life could form…

1 - Simple organic molecules such asamino acids & nucleotides

(ATGCU)

2 - Complex organic molecules such asproteins & nucleic acids

(DNA,RNA)

Current Scientific Theory about the Origin of the First Life Forms

4 Step Process:

1 - Chemical evolution2 - Polymerization3 - Microsphere formation4 - Protocell & Prokaryotic cell

formation

1-Chemical EvolutionInorganic

MoleculesWater - H2O

Methane - CH4

Ammonia - NH3

Hydrogen gas - H2

Organic MoleculesAmino acids (only

20)glycine, alanine, serine…

Nucleotides (only 5)adenine, thymine, cytosine, guanine, uracil

2 - POLYMERIZATIONProcess of joining 2 small organic

molecules (monomers) into larger more complex organic molecules (polymers)

3 - MICROSPHERESScientists 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 & PROKARYOTESOnce 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 Lab1 – 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