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.

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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

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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 !