Cell Biology I. Overview II. Membranes: How Matter Get in and Out of Cells III. Cellular Respiration IV. Photosynthesis V. DNA and Chromosome Structure VI. Protein Synthesis VII. Cellular Reproduction VIII. Origin of Life Hypotheses

VIII. Origin of Life Hypotheses Cell Biology VIII. Origin of Life Hypotheses Origin of life hypotheses Evolutionary Theory

A. The Early Earth and Earth History 4.5 bya: Earth Forms Graviational sorting of materials…heavy to the core, gases released under pressure…

The Early Earth and Earth History - Earliest Atmosphere - probably of volcanic origin Gases produced were probably similar to those released by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 and CH4

A. The Early Earth and Earth History 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks

A. The Early Earth and Earth History 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils Stromatolites - communities of layered 'bacteria'

A. The Early Earth and Earth History 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils Putative microfossil bacteria from Australia that date to 3.4 by

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen in Atmosphere 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 0.24 bya:Mesozoic 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 0.24 bya:Mesozoic 0.065 bya:Cenozoic 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 4.5 million to present (1/1000th of earth history) 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 0.24 bya:Mesozoic 0.065 bya:Cenozoic 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously Aleksandr Oparin (1894-1980) J.B.S. Haldane (1892-1964)

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously - Miller-Urey (1953) all biologically important monomers have been produced by these experiments, even while changing gas composition and energy sources

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously - Miller-Urey (1953) - Sydney Fox - 1970 - polymerized protein microspheres

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously - Miller-Urey (1953) - Sydney Fox - 1970 - polymerized protein microspheres - Cairns-Smith (1960-70) - clays as templates for non-random polymerization - 1969 - Murcheson meteorite - amino acids present; some not found on Earth. To date, 74 meteoric AA's. - 2004 - Szostak - clays could catalyze formation of RNA's

C. Acquiring the Characteristics of Life Three Primary Attributes: - Barrier (phospholipid membrane) - Metabolism (reaction pathways) - Genetic System

C. Acquiring the Characteristics of Life 1. Evolution of a Membrane - form spontaneously in aqueous solutions

A B C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - problem: how can pathways with useless intermediates evolve? These represent 'maladaptive valleys', don't they? A B C D E How do you get from A to E, if B, C, and D are non-functional?

A B C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution A B C D E

E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution suppose E is a useful molecule, initially available in the env. E

E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution suppose E is a useful molecule, initially available in the env. As protocells gobble it up, the concentration drops. E

D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution Anything that can absorb something else (D) and MAKE E is at a selective advantage... D E

D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution Anything that can absorb something else (D) and MAKE E is at a selective advantage... but over time, D may drop in concentration... D E

C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution So, anything that can absorb C and then make D and E will be selected for... C D E

A B C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution A B C D E and so on until a complete pathway evolves.

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Solution - reverse evolution Problem with “Miller-Urey Experiments” Requires source of continuous environmental energy AND carbon, and continual production of activated nucleotides to drive the reactions to form RNA. Lightening and other sources of energy do not provide the carbon, and they are unstable and destructively high energy

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Solution - reverse evolution Problem with “Miller-Urey Experiments” What’s Needed: Continuous flow of energy Continuous flow of carbon as source of new molecules Rudimentary catalysts (could be inorganic FeS minerals that are often at the heart of organic catalysts) “Focusing” products to raise their concentrations to reactive levels

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Solution - reverse evolution Problem with “Miller-Urey Experiments” What’s Needed: Continuous flow of energy Continuous flow of carbon Rudimentary catalysts “Focusing” products “Black Smokers” Very hot – 250-400oC, driven by magma in contact with water. Most stable carbon compound is CO2. Very unstable, collapsing in decades Do have lots of FeS compounds but precipitated organics would be blown from chimney.

Hydrothermal Vents

“White Smokers” of Today Hydrothermal Vents “White Smokers” of Today Mantle rock near spreading centers is exposed to sea water; the olivine (rich in ferrous iron) is oxidized by water in an exothermic reaction, giving off heat and H2. The warm (60-90oC), H-rich water percolates up and the carbonate minerals precipitate into microporous chimneys. High flux of carbon and energy is channeled over inorganic catalysts Thermal currents through pores can concentrate organics 1000 – 106 fold Vents persist for millennia 500 um

H+ The role of a proton gradient: If the formate (CO2- ) can accept a H+ to balance the charge, it won’t get rid of the electron. If the CO2 is placed in an acidic environment rich in H+, this will tend to happen. Likewise, if the free H+ is placed in an alkali environment (rich in OH-), it will bind to form stable water. The H2 has reacted with the CO2 irreversibly. If these fluids are separated by a thin inorganic membrane with FeS minerals, the FeS will draw the electrons from the H2 and transfer them to CO2. Physical structure of vent drives the synthesis of organics. These accumulate 1000x Pore Wall Seawater percolating through pores: pH = 6 H+ Percolating from mantle: pH = 11 OH- H2 FeS H2O CO2-2 + 2H+  CH2OO FeS 2e- 2 H+ e-

ATP STEP 2: Energy Harvest The proton gradient can be exploited by protein synthesized organically for Energy Harvest (ATP Synthase). So, both E harvest AND organic production ATP

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? DNA RNA (m, r, t) protein

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? DNA DNA stores info, but proteins are the metabolic catalysts... RNA (m, r, t) protein

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? - Ribozymes info storage AND cataylic ability

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? - Ribozymes - Self replicating molecules - three stage hypothesis

Stage 1: Self-replicating RNA evolves

(REPLICATION ENZYMES) Stage 1: Self-replicating RNA evolves RNA m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 2: RNA molecules interact to produce proteins... if these proteins assist replication (enzymes), then THIS RNA will have a selective (replication/reproductive) advantage... chemical selection.

(REPLICATION ENZYMES) DNA Reverse transcriptases m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 3: Mutations create new proteins that read RNA and make DNA; existing replication enzymes replicate the DNA and transcribe RNA.

Can this happen? Are their organisms that read RNA and make DNA?

Can this happen? Are their organisms that read RNA and make DNA? yes - retroviruses....

(REPLICATION ENZYMES) DNA m- , r- , and t- RNA Already have enzymes that can make RNA... PROTEINS (REPLICATION ENZYMES) Stage 3: Mutations create new proteins that read RNA and make DNA; existing replication enzymes replicate the DNA and transcribe RNA.

(REPLICATION ENZYMES) DNA m- , r- , and t- RNA Already have enzymes that can make RNA... PROTEINS (REPLICATION ENZYMES) Stage 3: Mutations create new proteins that read RNA and make DNA; existing replication enzymes replicate the DNA and transcribe RNA.

(REPLICATION ENZYMES) This is adaptive because the two-step process is more productive, and DNA is more stable (less prone to mutation). DNA m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 4: Mutations create new proteins that replicate the DNA instead of replicating the RNA...

(REPLICATION ENZYMES) This is adaptive because the two-step process is more productive, and DNA is more stable (less prone to mutation). DNA And that's the system we have today.... m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 4: Mutations create new proteins that replicate the DNA instead of replicating the RNA...

D. Summary: STEPS REQUIRED FOR THE SPONTANEOUS, NATURAL FORMATION OF LIFE, and the evidence to date: 1. Spontaneous synthesis of biomolecules - strong evidence; Miller-Urey experiments. 2. Polymerization of monomers into polymers (proteins, RNA, sugars, fats, etc.) - strong evidence;  Fox and Cairns-Smith experiments. 3. Formation of membranes - strong evidence; behavior of phospholipids in solution. 4. Evolution of metabolic systems - reasonable hypotheses, and genetic similarity in genes involved in particular pathways (suggesting gene duplication and subsequent evolution of new genes and elaboration of existing pathways) 5. Evolution of a genetic system - a reasonable hypothesis and significant corroborating evidence that it could happen. But no experimental evidence of the process evolving through all three steps. 6. How did these three elements (membrane, metabolism, genetic system come together?) a few untested hypotheses.