How Did Life Begin? And What is Life? Barry Selinsky Chemistry Department Villanova University

How was life established on earth?

God did it. God did it.

God School

God School – Final Written Examination As a community committed to the Augustinian ideals of truth, unity and love, God School prides itself on maintaining the highest standards of academic integrity and does not tolerate any forms of academic dishonesty or misconduct. Accordingly, each student who takes an examination is expected to sign the following statement: I, (sign your name) have not had any unsanctioned prior access to this examination and will conduct myself in an honest manner in regard to all aspects of this examination. Unless authorized, I will not discuss the contents of this examination with other students.

Final Thesis Project Create life. Create life. You may use any atomic materials up to and including the element iron. You may use any atomic materials up to and including the element iron.

Periodic Table

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

Final Written Examination - Continued You may also assume any environmental conditions needed to complete the assignment. You may also assume any environmental conditions needed to complete the assignment.

Good news and bad news The bad news – there is no partial credit. Either you make a living organism or you don’t. The bad news – there is no partial credit. Either you make a living organism or you don’t. The good news – you have 800 million years to complete the exam! The good news – you have 800 million years to complete the exam!

Assumptions in our attempts to determine how life began All of today’s organisms arose from a single ancestor organism. All of today’s organisms arose from a single ancestor organism. Support – all organisms today share many common features, proteins, and metabolic pathways. Support – all organisms today share many common features, proteins, and metabolic pathways.

Evolution in pictures

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

What is the simplest life as we know it? Bacteria – single cell organisms with the ability to independently reproduce and generate new bacteria. Bacteria – single cell organisms with the ability to independently reproduce and generate new bacteria.

Bacteria are comprised of numerous small molecules and four classes of macromolecules: Nucleic acids (DNA and RNA) Nucleic acids (DNA and RNA) Proteins Proteins Polysaccharides (polymers of sugars) Polysaccharides (polymers of sugars) Lipids Lipids

King of Prussia Mall: A Multicellular Organism

Costco – A Modern Single Celled Organism

The General store – A primitive single cell organism

Definitions of Life: Any population of entities which has the properties of multiplication, heredity, and variation. – John Maynard Smith Any population of entities which has the properties of multiplication, heredity, and variation. – John Maynard Smith Life is an expected, collectively self-organized property of catalytic polymers. – Stuart Kauffman Life is an expected, collectively self-organized property of catalytic polymers. – Stuart Kauffman Life possesses the properties of replication, catalysis, and mutability. – Norman Horowitz Life possesses the properties of replication, catalysis, and mutability. – Norman Horowitz

Definitions of life Life is a self-sustained chemical system capable of undergoing Darwinian evolution. – Gerald Joyce Life is a self-sustained chemical system capable of undergoing Darwinian evolution. – Gerald Joyce From this definition, what minimal elements must life contain? From this definition, what minimal elements must life contain?

1. Life must be chemical As a result, computer generated artificial intelligence is excluded. 2. Life sustains itself by gathering atoms and energy form its environment. If it doesn’t eat, it’s not alive. Life requires metabolism. 3. Living organisms must display variation. No two people, bunnies, or bacteria are necessarily the same. Life requires reproduction and genetic variability.

Bacteria are comprised of numerous small molecules and four classes of macromolecules: Nucleic acids (DNA and RNA; polymers of nucleotides) Nucleic acids (DNA and RNA; polymers of nucleotides) Proteins (polymers of amino acids) Proteins (polymers of amino acids) Polysaccharides (polymers of sugars) Polysaccharides (polymers of sugars) Lipids Lipids How can we make these?

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

Miller’s amino acid synthesis

Oro’s purine synthesis

Amino acids, sugars, purines, and pyrimidines can be made from simple precursors. Next, is it possible to generate polymers of these materials to make biomacromolecules important to life?

Polymerization on crystalline templates

The chirality issue

Chiral molecules

Order out of chaos: the entropy problem Second law of thermodynamics: Second law of thermodynamics: In any spontaneous process there is always an increase in the entropy of the universe.

The theory of “emergence” While systems become more disordered with time, local order and complexity arise due to the input of energy. While systems become more disordered with time, local order and complexity arise due to the input of energy.

The Iron-Sulfur World Hypothesis – life began at hydrothermal vents at the bottom of the ocean, fed by a constant stream of hot volcanic gas. Hypothesis – life began at hydrothermal vents at the bottom of the ocean, fed by a constant stream of hot volcanic gas.

Energy from volcanic gas

The Reverse Citric Acid Cycle

In support of the reverse citric acid cycle: At hydrothermal vents, there is a constant stream of hydrogen gas and energy generated from the reaction of hydrogen sulfide with iron sulfide. At hydrothermal vents, there is a constant stream of hydrogen gas and energy generated from the reaction of hydrogen sulfide with iron sulfide. The reactions can be catalyzed by iron sulfide, pyrite, or other iron-sulfur complex. The reactions can be catalyzed by iron sulfide, pyrite, or other iron-sulfur complex. In organisms, the reactions are catalyzed by enzymes. Most enzymes require iron-sulfur clusters to work. In organisms, the reactions are catalyzed by enzymes. Most enzymes require iron-sulfur clusters to work.

Problems with the Iron-Sulfur world The iron sulfur world does not explain the generation of genetic material, and does not include reproduction or genetic variability. The iron sulfur world does not explain the generation of genetic material, and does not include reproduction or genetic variability.

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

What is RNA?

Evidence in support of the RNA World Some RNA molecules can catalyze chemical reactions (mostly done by proteins). Some RNA molecules can catalyze chemical reactions (mostly done by proteins). Some RNA molecules can replicate themselves if ribonucleotides are present. Some RNA molecules can replicate themselves if ribonucleotides are present. This explains both metabolism and genetic variability. This explains both metabolism and genetic variability.

Problems with the RNA world Self-replicating RNA molecules have only been made up to 14 nucleotides long. Catalytic RNAs are estimated to require at least 50 nucleotides. Self-replicating RNA molecules have only been made up to 14 nucleotides long. Catalytic RNAs are estimated to require at least 50 nucleotides. There is no known physical encouragement for multiple self- replicating RNA molecules to collect in the same local area. There is no known physical encouragement for multiple self- replicating RNA molecules to collect in the same local area.

Thanks for living!