Origins of Life

*Cells only come from prexisting cells

Implication 1:

We can trace the origin of all the cells in our body to the zygote

Implication 2:

The origin of all cells can be traced to the LUCA, the last universal common ancestor

Implication 3:

There must have been a first cell (LUCA) that came from nonliving material

Prebiotic earth

• Frequent volcanic eruptions

• meteorites

  • brought water

• high temps

• lots of UV radiation

• literally hell

  • called the Hadean Eon

• Early atmosphere is mostly hydrogen and helium (quickly escaped)

• Second atmosphere

  • No ozone layer

  • Little oxygen

• Creates unique possibility for chemical reaction

Challenge of forming life

• Early earth conditions not good for life

• cells too complex to form by chance

Spontaneous generation: living organism from nonliving life

1. Simple organic molecules from inorganic ones

2. Organic compounds form polymers

3. self replication as basis for genetics

4. enclose in membrane

Organic from inorganic

Inorganic molecules (Water, carbon dioxide, etc) have random collisions to form organic collisions ( ie. amino acids, nitrogen bases, monosaccarides, fatty acids)

The Miller-Urey experiment (1953) was a model of early earth to see if they could get organic compounds

• Simulated ancient water cycle

• ocean - evaporation - atmosphere (included electricity)- condenser

• found amino acids

• prebiotic chemistry

• turned speculation into a testable science

Polymerization

• Second requirement for the formation of life

• Polymerization is the process in which small molecules combine to form large chain-like molecules called polymers

• Ex. Amino acids → proteins

Origins of inheritance (RNA)

RNA: Polymer formed by the formation of nucleotide monomers, probably came before DNA

RNA is a catalyst for their own replication

• Catalyst: substance that increases the rate of a chemical reaction

• can form copies of their own sequence without the use of enzymes

• RNA can also catalyze other biochemical reaction

• RNA makes things more efficient because it can make proteins

Early Membranes

The final requirement is that early cells needed a membrane to seperate outside from inside

• Made of phospholipids

  • hydrophobic tail

  • hydrophilic head

  • naturally form bilayes in water to form vesicles or micelles

Abiogenisis

Pasteur

He took a bunch of flasks and boiled them and had two flasks and broke one which had organism growth and the unbroken one had nothing in there

Disproved spontaneous generation occurring in current earth conditions

The OG Cell

Because spontaneous generation happened once but no longer does, all cells came from one ancestral cell

Cell is called LUCA

EVIDENCE

• All living cells have DNA as genetic material

  • DNA is translated into codons to form amino acids, 64 possible codons for 20 different amino acids to form proteins

• Study by Weiss et al

  • compared genomes of living bacteria and archaea

    • found only 355 homologous protein types (very small number)

  • Indicates that:

    • Bacteria and archea have been diverging for VERY long time

    • Any genes shared between them were inherited from LUCA

LUCA was probably not the first lifeform, but the older ones died off and have no progeny.

Estimating dates of the first cells

Genes are adapted to an organisms environment, so the genes likely would have been present in LUCA are a clue about how they lived

355 genes indicate that LUCA:

• Was an obligate anaerobe (did not use oxygen)

  • Little oxygen in early earth

• Was a chemoautotroph

Research done in Australia found 3.5 billion year old stromatolites were isotope dated and showed life

Eukaryotes

Two processes led to origin of eukaryotes

1. Infolding of plasma membrane

2. Endosymbiosis

Over time, the plasma membrane is thought to have folded inwards in ancestral prokaryotic cells. This is the origin of the single membrane organelles

Endosymbiosis: Origin of chloroplasts and mitochondria

symbiosis is an interaction between two things where both benefit, Endo means taken into cell but not digested

Chloroplasts and Mitchondria used to be independent prokaryotes until they started living in cells

*They became increasingly dependent on hosts

Mitochondria produces energy which is good for the cell, the mitochondria gets nutrients and protection. Same idea with chloroplasts, who don’t need to hunt for the sun.

Mitochondria came first

Evidence:

• Resemble bacterial structure

• They have their own internal membrane

• They have 70s ribosomes!

  • They can each make their own proteins, but they don’t because they are lazy (dependent on the cell)

• Are the same (approximate) size as prokaryotes

• Both chloroplasts and mitochondria have circular naked DNA

• DNA shares common sequence with modern prokaryotes.

• Move freely inside of the cell

• reproduce independently from the cell through binary fission

• are inhibited by antibiotics

Evolution of multicellularity

Advantages

• Longer life spans: death of one cell doesn’t affect others

• organisms can be larger: helps with survival

• complexity within the organisms: allows for variety of ecological functions