prebiotic chemstry jeff g. wardeska, phd jan. 24, 2008
TRANSCRIPT
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.
H2N CH C
CH3
OH
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.
N
NNH
N
NH2
Adenine
NH
NNH
N
O
NH2
Guanine
N
NH2
NH
NH
O
O
Thiamine
CytosineO
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.
N
NN
N
NH2
O
HOH
HH
HH
HO
Adenosine
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.
– 3. Proper conditions
N
NN
N
NH2
O
HOH
HH
HH
OP-O
O-
O
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.
• 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)
N
NNH
N
NH2
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
1. Large number of amino acids, > 50 not found on earth.
2. Slight enantiomeric excess of l-enantiomers in some.
3. Diff. 15N/14N ratio from terrestial samples. Same ratio in both d & l enantiomers.
Precambrian, cont’d. 3800. Oldest rocks,
oceans form. 3500-2800. 1st
prokaryotes, photosynthesis produces O2.
2800-1600. Banded Iron Formations.
Fe(II)
Fe(III)
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?
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