Origin of Life

Question 1

Chemical composition of Earth’s early (Archean) atmosphere

Answer 1

Lots and lots of carbon dioxide– made up the main composition. Also had significant portion of ammonia and methane compared to today.

Question 2

Miller & Urey Experiments

Answer 2

Demonstrated that by mimicking the early atmosphere, amino acids can be synthesized from inorganic molecule.

Question 3

Molecules to microbes:

Answer 3

Compound synthesis
phospholipid bilayer
replication (RNA, ribozymes)
Bilayers are perfect and allow molecules to enter and exit due to their fluidity.
Fatty acid membranes spontaneously separate into separate vesicles as they grow(replication)
RNA and fatty acid membranes likely occurred independently at first.
Putting it together: simple organic compounds form and eventually polymerize, self replication molecules(RNA) occur, self replicating machinery gets enclosed in a membrane, true cells with rna arise, modern cell DNA replaces RNa

Question 4

Role of mineral surfaces (clays) in concentrating and organizing organic molecules

Answer 4

Large surface area which serve as a template for organizing simple molecules into more complicated molecules
Long linear crystal structures, chemically attractive, huge surface area

Question 5

An Early RNA world as a precursor to the modern DNA world

Answer 5

RNA molecules are capable of catalyzing chemical reactions
RNA in ribosomes (“Ribozymes”) catalyze their own self replication w/o enzymatic mediators
RNA plays a key part in expression of DNA- indicating that Rna was key agent in catalysis and genetic coding in prebiotic world
Protein may have been recruited to assist in RNA replication, then other metabolic processes
Finally, may have been enclosed in a membrane.

Question 6

Molecular phylogeny & extremophiles – especially “hyperthermophile” bacteria & archaea

Answer 6

Hyperthermophiles are the lowest on the genetic tree, indicating life started there.

Question 7

Deep-sea hydrothermal vents

Answer 7

Likely the place where life started.
Enormous size of mid ocean ridges provide a variety of warm environs
Abundance of dissolved organic and inorganic compounds in warm environ- low oxygen levels
Somewhat Phosphorus rich
Releases metals (Zn, Ni) which life requires in trace amounts
Has clay for a template
Supports microbial community and has primitive bacteria and archaea
Protection from cosmic radiation (ozone layer)

Question 8

Green Sulfur Bacteria and anoxygenic photosynthesis

Answer 8

Infrared photosynthesis!! Found living near deep sea hydrothermal vents. Instead of taking H2O, it takes H2S, and instead of producing O2, they produce S.
H2S + CO2 => “CH2O” + S (shorthand)
Anoxygenic photosynthesis is the precursor to oxygenic photosynthesis

Question 9

Archean-aged terranes of Pilbara Craton, Australia

Answer 9

World class paleobiology sites.
Home of the oldest signs of life
3.4-3.5 billion year old prokaryote fossils are found here

Question 10

Oldest prokaryote fossils, stromatolites, how old?

Answer 10

3.5 Ga

Question 11

Cyanobacteria & oxygenic photosynthesis

Answer 11

CO2 + H2O -> CH2O + O2
Cyanobacteria are prokaryotes that engage in oxygenic photosynthesis
These form stromatolites
Oxygenic photosynthesis paved the way for aerobic metabolisms

Question 12

Oldest eukaryote fossils? When?

Answer 12

2Ga
Acritarchs - cysts of early eukaryotic algae
First eukaryotes evolved through endosymbiosis

Question 13

Endosymbiosis

Answer 13

casually enclosed prokaryotic cells which made up the organelles. The “enclosure” of some prokaryotic cells by other larger prokaryotic cells (one cell lives inside the other)

Question 14

3 pieces of evidence(Endosymbiosis):

Answer 14

Size of cells within eukaryotic cells nearly identical to free-living prokaryotes to which they are metabolically similar
Mitochondria and chloroplasts have cell membranes just like prokaryotic cells do
Organelles have their own DNA, RNA and ribosomes.

Question 15

Amino Acid Sequences: evidence of fusion of Archaea & Bacteria in evolution of eukaryotes

Answer 15

Organelles have their own RNA and DNA and ribosomes. ssrRNA sequences similar to bacteria
Proteins used by dna to package their dna in chromosomes, to transcribe dna, and to decode genetic messages remarkably similar to those used by eukaryotes
Based on ssrRNA sequences, archaea are more similar to eukaryotes than bacteria

Question 16

When did concentration of free molecular oxygen first start to rise?

Answer 16

The great oxygenation event around 2.5 - 2.3 Ga due to oxygenic photosynthesis by cyanobacteria

Question 17

Oldest fossils of multicellular organisms: What is the Ediacara Fauna? How old are these fossils?

Answer 17

570 Ma (late Pre-Cambrian)
Softbodied fossils preserved as impressions. First multicellular animals. Occurred worldwide. We don’t know their relationship with any other extant species.

Question 18

Fossil embryos (multicellular animals) in Doushantuo Formation of China – how old?

Answer 18

635-571 Ma

Fossil embryo and eggs- phosphatized eggs of bilaterally symmetrical animals

Question 19

compound synthesis

Answer 19

abundant organic compounds found in the universe are concentrated and synthesized on Earth (on clay minerals)

Question 20

phospholipid bilayer

Answer 20

cell membranes (made up of fatty acids and alcohol). Composed of a hydrophilic head and a hydrophobic group. Isolates interior chemistry from outside.