D1 Origin of Life on Earth IB Biology Option D D1 Origin of Life on Earth http://www.johnkyrk.com/evolution.html (Timeline of Origin of Life)

D.1.1 Describe four processes needed for the spontaneous origin of life on Earth The non-living synthesis of simple organic molecules: Obviously if nothing was alive yet, then the source of these molecules had to be abiotic We can presume that the early Earth had all of the base elements and compounds required They were somehow combined to make simple organic compounds Maybe the organic compounds were generated here, maybe they were extra-terrestrial!

D.1.1 Describe four processes needed for the spontaneous origin of life on Earth The assembly of these molecules into polymers: In order to make the larger molecules necessary for life, the simple organic compounds would have to polymerize The origin of self-replicating molecules made inheritance possible: DNA can’t self replicate, it needs protein enzymes However some RNA can self-replicate - it can catalyze the formation of copies of itself. They are called Ribozymes and are the basis of the RNA World Hypothesis

D.1.1 Describe four processes needed for the spontaneous origin of life on Earth 4) The packaging of these molecules into membranes with internal chemistry different from their surroundings: The formation of closed membranes an important step Closed membrane vesicles can form spontaneously from lipids This allowed differentiation between the internal and external environments http://www.ted.com/talks/martin_hanczyc_the_line_between_life_and_not_life.html?utm_source=newsletter_weekly_2011-11-11&utm_campaign=newsletter_weekly&utm_medium=email (On formation of protocell)

Can you identify these molecules? D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds Earth’s atmosphere was ‘reducing’ in the early days. It did not contain oxygen gas until after plants started photosynthesising Can you identify these molecules?

D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds Earth’s atmosphere was ‘reducing’ in the early days. It did not contain oxygen gas until after plants started photosynthesizing The atmosphere contained: Hydrogen Nitrogen Water vapour Methane Ammonia Hydrogen sulfide The gases came from abundant volcanic activity

D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds These monomers mixed in the ‘primordial soup’, shallow oceans with chemicals, where it is thought that they reacted to form biological molecules Miller and Urey tried to recreate these conditions in the lab in 1953 They were trying to demonstrate ‘chemical evolution’, the formation of more complex molecules from simpler stock in the primordial soup They combined the molecules from the previous page in a closed glass vessel (simulated atmosphere), they heated the water (simulated volcanic activity) and sparked electricity through the gases (simulated lightning)

D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds

D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds

D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds After a week they found: Thirteen of the twenty naturally occurring amino acids Around 15% of the carbon was now in organic compounds

Space is so empty, yet full of the potential for life D.1.3 State that comets may have delivered organic compounds to Earth Panspermia is the hypothesis that life on Earth originated from material delivered by a comet, either in the form of amino acids or as hardy bacteria Space is so empty, yet full of the potential for life Existing bacteria and archaebacteria have been found in odd and extreme environments on Earth: In hot springs, kilometres deep in the crust and even embedded in ice cores from deep inside Antarctica It is feasible that they could survive on or in a comet

D.1.3 State that comets may have delivered organic compounds to Earth Cosmic radiation could provide the energy for reactions that lead to the formation of complex organic molecules Analysis of the spectra of light coming from the comets reveals the presence of hydrocarbons, amino acids and peptides The bombardment of Earth by comets 4 billion years ago could have ‘kick started’ chemical evolution

D.1.3 State that comets may have delivered organic compounds to Earth The hypothesis that life came an extraterrestrial source: As previously mentioned, organic molecules are out there Mars is smaller than Earth and therefore cooled down more quickly, life could have begun there while Earth was still scorching Meteorites and comets impacting on mars could have thrown up debris with early life attached, this could then have crashed on Earth. Meteorites of Mars origin have been found in Antarctica

D.1.3 State that comets may have delivered organic compounds to Earth The hypothesis that life came an extraterrestrial source: There is no evidence that life has been transferred in this way. Every now and then there is a news story about “Fossils found in Mars meteorite” but so far this has not been confirmed The extraterrestrial hypothesis still doesn’t address how life formed, just how it could move around the galaxy

D. 1.4 Discuss possible locations where conditions would have allowed the synthesis of organic compounds Locations needed to be a reducing (electron adding) environment to encourage compound formation communities around deep-sea hydrothermal vents volcanoes extraterrestrial locations (carried to earth on a comet).

RNA shows enzymatic (catalytic) properties – called ribozymes D.1.5 Outline Two properties of RNA that would have allowed it to play a role in the origin of life RNAs can store, transmit and replicate genetic Information RNA is composed of a single helix. The bases are exposed and ready to combine with a complement, making replication simpler RNA was probably the first hereditary molecule having the ability to copy itself RNA shows enzymatic (catalytic) properties – called ribozymes Ribozyme: an RNA molecule that catalyzes a chemical reaction

D.1.5 Outline Two properties of RNA that would have allowed it to play a role in the origin of life Once RNA became enclosed in membranes, these protobionts would have a form of heredity. These protobionts may be selected for survival. RNA may have directed the sequencing of amino acids to form primitive enzymes.

Origin of cell formation D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings Origin of cell formation  Began as molecular aggregates  Separate inside from outside  Divide often (binary fission)  Grow larger in size  Maintain a level of homeostasis internally  Produce electrical potential across surfaces  Absorbs materials from the surface (selective permeability)  Catalytic actvity Bubbles… Tiny bubbles…

Protobionts = Aggregation of abiotically produced D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings Protobionts = Aggregation of abiotically produced molecules in droplets - Maintain an internal environment different from their surroundings. - Exhibit some properties associated with life: metabolism and reproduction - May have arisen from coacervates, microspheres, or liposomes

of polymeric molecules D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings Coacervate = droplets of polymeric molecules Colloidal suspension of macromolecules A water film acts as a barrier like a cell membrane Grows in size When large enough, it breaks down into small globules with the same traits as that of the “parent”

Microsphere = polypeptides with a semipermeable protein membrane D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings Microsphere = polypeptides with a semipermeable protein membrane formed by adding water to polypeptides show an electrical potential - may absorb materials from the surrounding environment membranes are made of phospholipid bilayers with proteins may give clues to the evolution of the cell membrane undergo shrinking and swelling due to osmosis

D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings Liposome = form spontaneously when the organic molecules includes lipids Form lipid bilayer membrane Grow by engulfing other liposomes and may split to form two

How Polymerization could Occur? D.1.6 State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings How Polymerization could Occur? Clay was thought to be a possible site for polymerization (rather than primordial soup in the sea) Binds well to organic molecules Contains Zinc, iron, nickel, etc serving as a catalyst Has been shown to occur experimentally: dry clay...heat it...200 amino acids can spontaneously join & form polypeptides!! ...can possibly form microspheres

Prokaryotes dominated life on Earth from 3.5–2.0 bya D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere Prokaryotes dominated life on Earth from 3.5–2.0 bya 3.5 billion year old fossil of bacteria modern bacteria chains of one-celled cyanobacteria

 Stromatolites offer more fossil evidence D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere Lynn Margulis  The first cells were prokaryotic  Stromatolites offer more fossil evidence – rocklike columns composed of many minute layers of prokaryotic cells (usually cyanobacteria)  Living stromatolite reefs are still found in hot springs and in warm, shallow pools of fresh and salt water

D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere Fossilized Stromatolites – 3.5 billion years old Modern day stromatolites

Oxygen begins to accumulate 2.7 bya D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere Oxygen begins to accumulate 2.7 bya reducing  oxidizing atmosphere evidence in banded iron in rocks = rusting makes aerobic respiration possible photosynthetic bacteria (cyanobacteria)

D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere first photosynthetic organism were autotrophs which split H2S as a hydrogen donor (purple and green sulfur bacteria) the first photosynthetic organisms to use H2O as a hydrogen donor were the cyanobacteria (released O2 as by-product) source of the first free oxygen in aquatic environment and atmosphere – O2 existed in significant quantities by 2 billion years ago

The increase in Oxygen led to: D.1.7 Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere The increase in Oxygen led to: The breakdown of the chemicals in the ‘chemical soup’ to carbon dioxide and oxidized sediments The formation of the ozone layer, which blocked out UV and stopped the production of more of the ‘soupy’ molecules The oxygen concentration rose to 0.45% of the atmosphere - not much compared to today’s 21%, but it led to the rise of the eukaryotes

D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes Endosymbiosis is the theory that chloroplasts and mitochondria were once free-living prokaryotes that were engulfed by larger prokaryotes and survived to evolve into the modern organelles

First Eukaryotes Development of internal membranes ~2 bya D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes First Eukaryotes ~2 bya Development of internal membranes create internal micro-environments advantage: specialization = increase efficiency nuclear envelope endoplasmic reticulum (ER) plasma membrane infolding of the plasma membrane nucleus DNA cell wall plasma membrane Prokaryotic cell Prokaryotic ancestor of eukaryotic cells Eukaryotic cell

Endosymbiosis D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes Endosymbiosis Evolution of eukaryotes origin of mitochondria engulfed aerobic bacteria, but did not digest them mutually beneficial relationship internal membrane system aerobic bacterium mitochondrion Endosymbiosis Ancestral eukaryotic cell Eukaryotic cell with mitochondrion

Endosymbiosis Evolution of eukaryotes D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes Eukaryotic cell with mitochondrion Endosymbiosis Evolution of eukaryotes origin of chloroplasts engulfed photosynthetic bacteria, but did not digest them mutually beneficial relationship photosynthetic bacterium chloroplast mitochondrion Endosymbiosis Eukaryotic cell with chloroplast & mitochondrion

Theory of Endosymbiosis D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes Theory of Endosymbiosis Evidence structural mitochondria & chloroplasts resemble bacterial structure genetic mitochondria & chloroplasts have their own circular DNA, like bacteria functional mitochondria & chloroplasts move freely within the cell mitochondria & chloroplasts reproduce independently from the cell