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