Origin of Life

Eons – largest time division Eons determined by major changes in the Earth Most recent Eon started with the appearance of multicellular animals = Phanerozoic Eon Three Eons make up what was previously know as the Precambrian Period 1) Proterozoic 2) Archean 3) Hadean

I. WHEN Did Life Evolve? A) Earth molten for Hadean Eon (4.5 – 3.9 bya) B) cooled by 3.9 billion years ago C) Solid rock formation began Archean Eon 3.9 bya

II. First life likely formed in water A) water vapor condenses and falls as rain B) Creates oceans C) salts added over billions of years as material eroded from continents D) water protects from U-V radiation

III. First cell = anaerobic conditions A) Early Archean rock dark-colored = unoxidized B) Formed before free O2 available C) oxidized (rusted) sediment appears 2.2 billion years ago in Proterozoic Eon D) Free oxygen produced by living cells doing .… photosynthesis E) Therefore, life must have evolved before 2.2 bya

IV. How did the first cell form? A) Spontaneous formation of monomers and macromolecules from chemicals in environment **** Only possible if no free O2 B) cell membranes form C) nucleic acids pass on Genetic infromation

V. Monomer Synthesis A. we created organic monomers from non-living chemicals B.Miller and Urey - created “Early Earth Apparatus” C. Archaean atmosphere D. electrodes produce “lightning” E. primordial pond in the bottom

F. Results: 12 of 20 most common amino acids synthesized + monomers Showed monomers can form from non-living source next step: polymerization

VI. Requirements for polymerization A. energy source: 1. lightning 2. geothermal vents B. concentration: to bring materials together 1. tide pools/evaporation 2. clay

clay a. Forms platelets b. platelets are: very small flat with negative charge on surface

VII. Cell membrane formation A) phospholipids amphipathic hydrophobic & hydrophilic B) form spheres in water C) hydrophobic ends protected on inside D) First cell membrane?

VIII. Protobionts/protocells A) fatty acid spheres form naturally B) Macromolecules & enzymes inside C) reactions occur inside D) Grow E) divide F)selectively permiable G) digest starch H) store & release energy

Experiments by Sidney W. Fox and Sidney w Experiments by Sidney W. Fox and Sidney w. Fox and Aleksandr Oparin have demonstrated that protobionts form spontaneously. They formed liposomes and microspheres, which have membrane structure similar to the phospholipid bilayer found in cells may be formed spontaneously, in conditions similar to the environment thought to exist on an early Earth. These experiments formed

I. Are Protobionts Alive? 1)No 2) they can’t replicate themselves (pass on their traits to offspring)

IX. Replication A) process by which organisms make genetic copies of themselves asexual reproduction 2) sexual reproduction

X. Origin of Heredity A) many different types of protobionts B) those best able to accumulate organic molecules, grow, and divide become most common C) but “competition” is useless unless traits can be passed on/inherited D) need polymers that can replicate themselves: DNA and RNA

XI. Nucleic acid reproduction A) RNA can assemble on its own (Zn catalyst) B) Can replicate (make more copies) C) Can pass on genetic info when cell divides D) RNA world Hypothesis

XII. Earliest Life Forms 3.5 bya 3.4 byo, South Africa A) prokaryotic bacteria B) anaerobic: live without O2 C) fermenters: use organic molecules for energy modern

XIII. The First Energy Crunch A) organic molecules become scarce B) competitive advantage goes to – C) organisms that can make their own food Photosynthesis D) done by primitive cyanobacteria

Photosynthesis 1) light-absorbing pigments (like chlorophyll) already present 2) chlorophyll rings form spontaneously 3) mutation causes e- to jump out 4) leads to Anaerobic cyclic psyn Makes only a little ATP (no glucose)

Aerobic Non-cyclic Photosynthesis some cyanobacteria evolved to use H2O as e- source O2 released as a by-product Advantage: glucose produced = storable energy Problem: O2 toxic to anaerobic cells 6CO2 + 6H2O carbon dioxide water C6H12O6 + 3O2 sugar oxygen energy from sunlight

Indirect (non-fossil) evidence Build up of oxygen Indirect (non-fossil) evidence for the presence of cyanobacteria ~ 3.5 bya

BIFs (Banded Iron Formations) Indirect evidence for the presence of cyanobacteria ~ 3.5 bya Precambrian, Australia

Banded Iron Formations Created iron dissolves in anaerobic water when iron bonds to O2 it becomes solid Iron oxide deposited in red layers When dissolved iron used up : 1) cyanobacteria die 2) dark, un-oxidized layers build up

Why are BIFs Banded? When runoff added more Fe to the water the entire process stared over again.

What Likely Happened O2 made by cyanobacteria at ocean surface O2 toxic to them but not if the O2 was removed by bonding with iron (Fe) Oceans contained dissolved iron

BIFs began forming 3.5 bya = 1st free O2 ended about 1.8 bya = constant free O2

Earliest (Undisputed) Fossils = Stromatolites 2.2 byo Michigan

Stromatolites dome-shaped, layered structures Up to 3.5 byo consist of layers of bacteria upper layers aerobic, photosynthetic lower layers anaerobic produce abundant oxygen how do we know?

They are still alive today in special environments, notably Shark Bay, Australia Tide In Tide Out

Formation of Stromatolites Cyanobacteria form a mat on top of sediment A new layer of sediment is deposited on top 1 cm Bacteria grow up through new layer

Stromatolites provide evidence for the occurrence of cyanobacteria in the fossil record. Modern Ancient

Aerobic Bacteria some bacteria evolved antioxidants allowed them to survive rising O2 levels by 1.8 bya some evolved to use O2… = aerobic respiration Obligate anaerobe bacteria restricted to refuges or go extinct

The rise of cyanobacteria & build up of oxygen in atmosphere had three significant effects: Aerobic photoautotrophs became producers that fuel the food chains of surface world The first mass extinction oxygen-rich atmosphere set stage for the multicellular life (aerobic respiration)

Eukaryotic Cells First well established fossils 1.7 bya Mid-Proterozoic eon Early protists unicellular with nucleus 100x larger than bacteria

Origin of Nucleus & E. R. In-folding of cell membrane Similar to bacterial psyn membrane Surrounded DNA Formed ER

Endomembrane system and nuclear envelope are continuous

‘In eukaryotes the organelles of the endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes and the cell membrane. The system is defined more accurately as the set of membranes that form a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport.’ https://en.wikipedia.org/wiki/Endomembrane_system

Origin of Mitochondria & Chloroplasts Endosymbiotic theory Eukaryotic cells take in bacteria as endosymbionts Aerobic Bacteria become mitochondria Cyanobacteria become chloroplasts

Evidence for Endosymbiotic T 1) Two membrane layers of A) Outer membrane like host cell B) Inner membrane like a bacteria

2) Mito. & chloro. have their own DNA Circular Chromosome Different genes than nucleus

3) Mito. & Chloro have own ribosomes & Make own proteins Ribosomes like bacteria

4) Mito & Chloro grow and reproduce on own