How Did Life Begin?How Did Life Begin?And What is Life?And What is Life?

Barry SelinskyBarry Selinsky

Chemistry DepartmentChemistry Department

Villanova UniversityVillanova University

How was life established How was life established on earth?on earth?

•God did it.God did it.

God SchoolGod School

God School – Final Written God School – Final Written ExaminationExamination

As a community committed to the Augustinian As a community committed to the Augustinian ideals of truth, unity and love, God School ideals of truth, unity and love, God School prides itself on maintaining the highest prides itself on maintaining the highest standards of academic integrity and does standards of academic integrity and does not tolerate any forms of academic not tolerate any forms of academic dishonesty or misconduct. Accordingly, dishonesty or misconduct. Accordingly, each student who takes an examination is each student who takes an examination is expected to sign the following statement:expected to sign the following statement:

I, (sign your name)I, (sign your name)have not had any unsanctioned prior access have not had any unsanctioned prior access

to this examination and will conduct myself to this examination and will conduct myself in an honest manner in regard to all aspects in an honest manner in regard to all aspects of this examination. Unless authorized, I of this examination. Unless authorized, I will not discuss the contents of this will not discuss the contents of this examination with other students.examination with other students.

Final Thesis ProjectFinal Thesis Project

• Create life.Create life.

• You may use any atomic materials up You may use any atomic materials up to and including the element iron. to and including the element iron.

Periodic TablePeriodic Table

Final Written Examination - Final Written Examination - ContinuedContinued

• You may also use You may also use small molecules small molecules consisting of no consisting of no more than 5 total more than 5 total atoms and no more atoms and no more than 3 different than 3 different elements. That is, elements. That is, water and HCN are water and HCN are ok; acetate ok; acetate (CH(CH33COOH) is not.COOH) is not.

H

O

HH C N

C C

H

H

HO H

O

Final Written Examination - Final Written Examination - ContinuedContinued

• You may also You may also assume any assume any environmental environmental conditions needed conditions needed to complete the to complete the assignment.assignment.

Good news and bad newsGood news and bad news

• The bad news – there is no partial The bad news – there is no partial credit. Either you make a living credit. Either you make a living organism or you don’t.organism or you don’t.

• The good news – you have 800 The good news – you have 800 million years to complete the exam!million years to complete the exam!

Assumptions in our attempts to Assumptions in our attempts to determine how life begandetermine how life began

• All of today’s organisms arose from a All of today’s organisms arose from a single ancestor organism.single ancestor organism.

• Support – all organisms today share Support – all organisms today share many common features, proteins, many common features, proteins, and metabolic pathways.and metabolic pathways.

Evolution in picturesEvolution in pictures

Corollary to first assumptionCorollary to first assumption

• If multiple types of organisms If multiple types of organisms developed simultaneously (or nearly developed simultaneously (or nearly so), one type dominated and so), one type dominated and eliminated the others.eliminated the others.

What is the simplest life as we What is the simplest life as we know it?know it?

• Bacteria – single cell organisms with the ability to Bacteria – single cell organisms with the ability to independently reproduce and generate new independently reproduce and generate new bacteria.bacteria.

Bacteria are comprised of Bacteria are comprised of numerous small molecules and numerous small molecules and four classes of four classes of macromolecules:macromolecules:• Nucleic acids (DNA and RNA)Nucleic acids (DNA and RNA)

• ProteinsProteins

• Polysaccharides (polymers of sugars)Polysaccharides (polymers of sugars)

• LipidsLipids

King of Prussia Mall: A King of Prussia Mall: A Multicellular OrganismMulticellular Organism

Costco – A Modern Single Costco – A Modern Single Celled OrganismCelled Organism

The General store – A primitive The General store – A primitive single cell organismsingle cell organism

Definitions of Life:Definitions of Life:

• Any population of entities which has the Any population of entities which has the properties of multiplication, heredity, and properties of multiplication, heredity, and variation.variation. – John Maynard Smith – John Maynard Smith

• Life is an expected, collectively self-Life is an expected, collectively self-organized property of catalytic polymers.organized property of catalytic polymers. – – Stuart KauffmanStuart Kauffman

• Life possesses the properties of Life possesses the properties of replication, catalysis, and mutability.replication, catalysis, and mutability. – – Norman HorowitzNorman Horowitz

Definitions of lifeDefinitions of life

• Life is a self-sustained chemical Life is a self-sustained chemical system capable of undergoing system capable of undergoing Darwinian evolution.Darwinian evolution. – Gerald Joyce – Gerald Joyce

• From this definition, what minimal From this definition, what minimal elements must life contain?elements must life contain?

1.1. Life must be chemicalLife must be chemicalAs a result, computer generated artificial As a result, computer generated artificial

intelligence is excluded.intelligence is excluded.2.2. Life sustains itself by gathering atoms Life sustains itself by gathering atoms

and energy form its environment.and energy form its environment.If it doesn’t eat, it’s not alive. Life If it doesn’t eat, it’s not alive. Life

requires metabolism.requires metabolism.3.3. Living organisms must display Living organisms must display

variation.variation.No two people, bunnies, or bacteria are No two people, bunnies, or bacteria are

necessarily the same. Life requires necessarily the same. Life requires reproduction and genetic variability.reproduction and genetic variability.

Bacteria are comprised of Bacteria are comprised of numerous small molecules and numerous small molecules and four classes of four classes of macromolecules:macromolecules:• Nucleic acids (DNA and RNA; Nucleic acids (DNA and RNA;

polymers of nucleotides)polymers of nucleotides)

• Proteins (polymers of amino acids)Proteins (polymers of amino acids)

• Polysaccharides (polymers of sugars)Polysaccharides (polymers of sugars)

• LipidsLipids

How can we make these?How can we make these?

Miller’s experiments: Miller’s experiments: A A production of amino acids production of amino acids under possible primitive earth under possible primitive earth conditions.conditions.

Miller’s amino acid Miller’s amino acid synthesissynthesis

C

H

H H

H

N

H

H H

H H N

C

H H

C

O

H

H H

O

H2O

+ +

methane 2:

ammonia 2:

hydrogen 1

glycine(an amino acid

Oro’s purine synthesisOro’s purine synthesis

H C N

N

NN

N

H

NH2

hydrogen cyanide(poisonous gas)

adenine (forms adenosinetriphosphate (ATP), DNA, and RNA

Amino acids, sugars, purines, Amino acids, sugars, purines, and pyrimidines can be made and pyrimidines can be made from simple precursors.from simple precursors.

Next, is it possible to generate Next, is it possible to generate polymers of these materials to polymers of these materials to make biomacromolecules make biomacromolecules important to life?important to life?

Polymerization on crystalline Polymerization on crystalline templatestemplates

The chirality issueThe chirality issue

Chiral moleculesChiral molecules

Order out of chaos: the entropy Order out of chaos: the entropy problemproblem

• Second law of Second law of thermodynamics:thermodynamics:

In any spontaneous In any spontaneous process there is process there is always an increase always an increase in the entropy of in the entropy of the universe.the universe.

The theory of “emergence”The theory of “emergence”

• While systems While systems become more become more disordered with disordered with time, local order time, local order and complexity and complexity arise due to the arise due to the input of energy.input of energy.

The Iron-Sulfur WorldThe Iron-Sulfur World

• Hypothesis – life Hypothesis – life began at began at hydrothermal vents hydrothermal vents at the bottom of at the bottom of the ocean, fed by a the ocean, fed by a constant stream of constant stream of hot volcanic gas.hot volcanic gas.

Energy from volcanic gasEnergy from volcanic gas

Feo + H2S FeS + H2 + energy

FeS + H2S FeS2 + H2 + energy

The Reverse Citric Acid The Reverse Citric Acid CycleCycle

Pyruvate Acetyl-CoA

Citrate

Aconitate

Isocitrate

2-Oxoglutarate

Succinyl-CoA

Succinate

Fumerate

Malate

Oxaloacetate

CO2

H2

H2O

H2

CoA

CO2

H2CO2

H2O

H2O

CoA

CO2

In support of the reverse citric In support of the reverse citric acid cycle:acid cycle:

• At hydrothermal vents, there is a constant At hydrothermal vents, there is a constant stream of hydrogen gas and energy stream of hydrogen gas and energy generated from the reaction of hydrogen generated from the reaction of hydrogen sulfide with iron sulfide.sulfide with iron sulfide.

• The reactions can be catalyzed by iron The reactions can be catalyzed by iron sulfide, pyrite, or other iron-sulfur complex.sulfide, pyrite, or other iron-sulfur complex.

• In organisms, the reactions are catalyzed In organisms, the reactions are catalyzed by enzymes. Most enzymes require iron-by enzymes. Most enzymes require iron-sulfur clusters to work.sulfur clusters to work.

Problems with the Iron-Sulfur Problems with the Iron-Sulfur worldworld

• The iron sulfur world does not explain The iron sulfur world does not explain the generation of genetic material, the generation of genetic material, and does not include reproduction or and does not include reproduction or genetic variability.genetic variability.

The RNA WorldThe RNA World

• Hypothesis: Life began as a Hypothesis: Life began as a collection of a small number of self-collection of a small number of self-reproducing catalytic RNA molecules reproducing catalytic RNA molecules localized within a small area.localized within a small area.

What is RNA?What is RNA?

Evidence in support of the RNA Evidence in support of the RNA WorldWorld

• Some RNA molecules can catalyze Some RNA molecules can catalyze chemical reactions (mostly done by chemical reactions (mostly done by proteins).proteins).

• Some RNA molecules can replicate Some RNA molecules can replicate themselves if ribonucleotides are themselves if ribonucleotides are present.present.

• This explains both metabolism and This explains both metabolism and genetic variability.genetic variability.

Problems with the RNA Problems with the RNA worldworld

• Self-replicating RNA molecules have Self-replicating RNA molecules have only been made up to 14 nucleotides only been made up to 14 nucleotides long. Catalytic RNAs are estimated long. Catalytic RNAs are estimated to require at least 50 nucleotides.to require at least 50 nucleotides.

• There is no known physical There is no known physical encouragement for multiple self-encouragement for multiple self-replicating RNA molecules to collect replicating RNA molecules to collect in the same local area.in the same local area.

Thanks for living!Thanks for living!