Transcript Prebiotic Chemstry

Prebiotic Chemstry
Jeff G. Wardeska, PhD
Jan. 24, 2008
Two Questions
1. How were the molecules necessary
for the first living organisms
synthesized?
 2. Could life as we know it exist
elsewhere in the universe?

1. How were the necessary
molecules for the first living
organisms synthesized?

What molecules are needed to make
the simplest cell, e.g., virus?
1. How were the necessary for
the first living organisms
synthesized?

What molecules are needed to make the
simplest cell, e.g., virus?
– 1. Protein; 20 amino acids.
O
H2N
CH
CH3
C
OH
1. How were the necessary
molecules for the first living
organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?
– 1. Protein; 20 amino acids.
– 2. DNA; 4 bases (A, G, C, T), PO4-3, ribose.
O
NH2
N
N
N
H
N
N
H
N
NH
N
NH
N
O
NH2
O
NH2
N
H
Cytosine
Adenine
Guanine
Thiamine
O
1. How were the necessary
molecules for the first living
organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?
– 1. Protein; 20 amino acids.
– 2. DNA; 4 bases (A, G, C, T), PO4-3, ribose.
NH2
N
N
HO
O
H
H
OH
H
H
H
Adenosine
N
N
1. How were the necessary
molecules for the first living
organisms synthesized?

What molecules are needed to make the simplest cell, e.g., virus?
– 1. Protein; 20 amino acids.
– 2. DNA; 4 bases (A, G, C, T), PO4-3, ribose.
NH2
– 3. Proper conditions
N
N
O
-O
P
O
O
O-
H
H
OH
H
H
H
N
N
Today’s Atmosphere
Oxidizing: N2, O2, CO2, H2O
 Organic Molecules are oxidized.
 CH4 + 2 O2 -> CO2 + 2 H2O
 Unique to Earth.
 Fe3+; Fe(OH)3, Ksp ~ 10-39.

A. I. Oparin, 1938
The Origin of Life. (Dover, 2nd edition)
 Original atmosphere- reducing.
 H2, CO, CH4, NH3, H2O, (H2S).
 Oxygen is the result of Life on Earth.
 Fe2+ primary form of iron.

Miller-Urey Experiment
1950.
 Reacted Mixture of
CH4, NH3, H2, H2O.

Miller-Urey Experiment


•
•
1950.
Reacted Mixture of
CH4, NH3, H2, H2O.
Produced about 20
amino acids (<2%
yield, each),+ HCN.
Reacted about 15%
of C.
Miller-Urey, cont’d

Can form amino acids
under a variety of
conditions;
–
–
–
–
–
–
UV light energy.
Sound.
Heat.
+ H2S -> cysteine.
HCN -> A, G
+HCCCN -> C, U
(Cyanoacetylene)
NH2
N
N
H
N
N
Adenine = (HCN)5
H
C
C
C
N
What’s the evidence
that this chemistry
might have actually
happened?
Murchison Meteorite, Australia, 1969.
 Geologic Record.

Murchison Meteorite

Sept. 1969, Australia
Murchison Meteorite
1. Large number of amino acids, > 50
not found on earth.
 2. Slight enantiomeric excess of lenantiomers in some.
 3. Diff. 15N/14N ratio from terrestial
samples. Same ratio in both d & l
enantiomers.

Precambrian Era, Mya
Fe(III)
Fe(II)
Precambrian, cont’d.


Fe(III)

Fe(II)
3800. Oldest rocks,
oceans form.
3500-2800. 1st
prokaryotes,
photosynthesis
produces O2.
2800-1600.
Banded Iron
Formations.
Stromatolites
Banded Iron Formations
Issues
Origin of l-forms of amino acids.
 Mechanism of synthesis of
nucleosides and nucleotides.
 Chicken vs. egg; which came first,
DNA or proteins?

– RNA world?
Are we alone?
Further reading

Stanley L. Miller and Leslie E. Orgel, “The Origins
of Life on the Earth”, Prentice-Hall, 1974.

Antonio Lazcano* and Stanley L. Miller, “The Origin
and Early Evolution. Review of Life: Prebiotic
Chemistry”, the Pre-RNA World, and Time. Cell,
Vol. 85, 793–798, June 14, 1996.

Leslie E. Orgel, “Prebiotic Chemistry and the Origin
of the RNA World”, Critical Reviews in Biochemistry
and Molecular Biology, 39:99–123, 2004
Thank You!