PTYS 214 – Spring 2011 Homework #2 DUE in class TODAY Homework #3 available for download on the...
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Transcript of PTYS 214 – Spring 2011 Homework #2 DUE in class TODAY Homework #3 available for download on the...
PTYS 214 – Spring 2011
Homework #2 DUE in class TODAY
Homework #3 available for download on the class website DUE Thursday, Feb. 3
Useful Reading: class website “Reading Material” http://en.wikipedia.org/wiki/Origin_of_life http://www.talkorigins.org/faqs/abioprob/originoflife.html http://sandwalk.blogspot.com/2009/05/metabolism-first-and-origin-of-life.html
Announcements
Homework #1
Total Students: 29
Class Average: 7.5
Low: 4
High: 10
If you have questions see Lissa 3 4 5 6 7 8 9 10 11
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Metabolism-first vs. Replication-first
Both theories have a problem with low probability events:
– Metabolism-first: bringing together the right sets of metabolic paths in an enclosed setting
– Replication-first: bringing together a self-replicating polymer
Neither has been reproduced in the laboratory Some new results:
Feb. 2009: “Self-sustained replication of an RNA enzyme”, Lincoln and Joyce, Science 323, p.
1229
Open (lively!) debate
Bottom-Up Strategy: Primordial Soup Theory
Life began in a warm pond/ocean from a
combination of basic building blocks of life (organic
molecules) into ever more complex organic molecules,
such as amino acids, proteins, and some early
version of RNA
Where did the building blocks of life came from?
Building Blocks of Life: Atmosphere
Almost all organic carbon which we observe today is produced biologically (via photosynthesis):
CO2 + H2O CH2O + O2 (CH2O – any organic matter)
Carbon which comes out of volcanoes is in a form of CO2
CO2 gas mixture does not produce organic molecules on its own
inorganicorganic
Recipe for a Primordial Soup
Find it on YouTube at: http://www.youtube.com/watch?v=7pt0rIZ3ZNE
CH4
NH3
H2O
C
H
N
O
HCN (cyanide)
H2CO (fomadehyde)
Amino acids
Other simple organics
Spark discharge breaks the chemical bonds in CH4,
NH3, H2O
C, H, N, O atoms can recombine into various organic molecules that eventually end up into
the oceans
Urey-Miller Experiment in ShortA
ncie
nt a
tmos
pher
e
Problems of organic synthesis via Urey-Miller experiment
It is hard to justify large amounts of NH3 and CH4 in the early (prebiotic) atmosphere
In a CO2-rich atmosphere organic production by spark discharge is not very efficient – dilution problem
If CH4/CO2 < 0.1 essentially no organic production
CONONO2
H2O
O >> C,N,HCO2 >> CH4, NH3
In an atmosphere dominated by CO2 the most abundantradical after spark discharge or photolysis is O
“Bad” CO2 Atmosphere
The dominant species after recombination are inorganic molecules!
Current Research: organic production in CO2-N2-H2 mixtures
Building Block of Life: Hydrothermal Vents
Find it on YouTube: http://www.youtube.com/watch?v=D69hGvCsWgA
Organic synthesis in Hydrothermal Vents
Hydrothermal vents were likely to be present in the prebiotic environment
Synthesis requires only CO2, H2O and silicate rocks
Processes Involved (Fischer-Tropsch - high T and P) Serpentinization:
Spinel polymerization:
Olivine + Serpentine + Magnetite(spinel group)
Seawater & dissolved CO2
Hematite
Major hydrothermal vent sites © Dr. Sven Peterson – IFM-GEOPMAR, Keil
Problems with organic synthesis via Hydrothermal Vents
Only very simple organics are generated (no amino acids, etc.)
Any complex organics are unstable at high temperatures (they are not around long enough to form larger macromolecules)
Hydrothermal Vents:Organics are unstable at high temperatures
1) Organic molecules could form away from vents, where temperatures are lower (it is a steep gradient!)
2) Expandable clay (smectites) surrounding the hydrothermal vents might serve as a “primordial womb" for infant organic molecules, sheltering them within its mineral layers
Williams et al. (2005) Geoloby 33, p. 913
Can you think of any other source of organic matter?
Both atmosphere and hydrothermal vents have problems producing complex organics
Space!
Extraterrestrial origin – organic material was synthesized in space and was brought to Earth somehow
~150 interstellar and circumstellar molecules
H2
CH2
C6H6
NH3
Glycine
Giant molecular cloud
Star formation
Do we have examples of extraterrestrial material on Earth?
Meteorites!
Murchison (1969, Australia)
MeteoritesNatural objects originating in outer space that
survive an impact with the Earth's surface without being destroyed
Chondrites – 86% (oldest rocks in the solar system)
5% are Carbonaceous Chondrites
Achondrites – 8%
Irons – 5%
Some of the amino acids synthesized in the Miller-Urey experiment and also found in the Murchison meteorite
Problems with Extraterrestrial Organic Delivery
Simple organics only – no large macromolecules
It is hard to accumulate necessary mass of carbon for the “concentrated” prebiotic soup (dilution problem)
Building Blocks or Life:The Phosphorus Problem
Cosmic DNA
H 2.8 × 106 10
O 1400 6
C 680 9.5
N 230 3.75
S 43 0
P 1 1
Phosphorus is a very rare element in the universe
On Earth it is found as insoluble phosphate minerals
Life selects phosphorus!
Phosphorous is in nucleic acids (DNA,RNA)
(like phospholipids and ATP)
…and other important organic macromolecules
Extraterrestrial P
Two forms:– Phosphate
Ca5(PO4)3(OH,F)
like typical phosphates on Earth
– Schreibersite
(Fe,Ni)3P
NOT a naturally-occurring crustal mineral
Seymchan meteorite (pallasite) 20 cm
Phosphorus on the Earth’s surface
Phospates are not soluble in water at normal terrestrial conditions
Schreibersite rusts in presence of water to form soluble and reactive P
Meteorites may be an important source of P for the origin of life
Pasek (2008) “Rethinking early Earth phosphorus geochemistry” PNAS 105(3), p.853
Bottom-Up Approach - Summary1. Small organic molecules
Small organic carbon molecules could have come from three sources in the prebiotic world:
1)Synthesis in the atmosphere2)Synthesis in the hydrothermal vents3) Synthesis in space and delivery via meteorites
Bottom-Up Approach - Summary 2. Subunits of RNA
Phosphates: rock (meteorite) weathering
Ribose: CO2 + H2O + Energy 5 CH2O + H2O Ribose
Base: CH4 + N2 + Energy 5 HCN Adenine
(formaldehyde)
(and similar reactions for the other 3 RNA bases)
(hydrogen cyanide)
- Formation of longer molecules from simple organic molecules
Dehydration reaction: two simpler organic molecules are bonded through the loss of water
Bottom-Up Approach - Summary
3. Polymerization
H2O
Primordial soup was probably too dilute in simple monomers to form very long molecules
Possible concentration mechanisms: Heat from expelled lavas (eg. St. Helens) Tidal pools (evaporation) Freezing water Mineral catalysts (clays)
All of them are quite inefficient compared to enzymes and cells
The Dilution Problem
Minerals can help polymerization
Minerals (like clay and pyrite) can provide a repeating pattern to act as a template for polymerization
Small organic molecules could have stuck to the mineral surface (organic film)
Kaolinite
Quiz Time !