IB HL Biology - Origin of Cells

Conditions of early Earth

1) high temperature due to the higher levels of carbon dioxide and methane
2) UV radiation: lacked free oxygen= no ozone layer, which means UV radiation was not absorbed
3) Volcanic eruptions
4) Lightning
5) Reducing atmosphere: less oxygen

how did carbon compounds form?

1) formation of organic compounds from inorganic compounds
2) assembly of carbon compounds into polymers
3) polymers self-replicate and acts as catalysis such as RNA
4) compartmentalization: polymer molecules are packaged into membranes to distinguish the internal chemistry of a cell from the external chemistry

Urey-Miller Experiment

1) boil water to produce steam, recreating primordial soup evaporating in the high temperatures of early Earth (represents the ocean)
2) mix steam with a mixture of gases such as methane, hydrogen and ammonia to recreate the atmosphere
3) add electrical discharges to stimulate lightning which is a source of energy
4) cool the mixture

-> after a week, there were traces of simple organic molecules, which suggested that it was possible for carbon compounds to form spontaneously

Cell theory

idea that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from pre-existing cells

all cells:
- are enclosed by a plasma membrane
- store genetic information in DNA molecules

8 life processes

1) Nutrition
2) Transport
3) Synthesis
4) Growth
5) Excretion
6) Respiration
7) Regulation
8) Reproduction

Viruses are non-living

- they are not made up of cells
- do not grow
- can not replicate
- can not perform independent metabolism
- cannot self regulate

Spontaneous origin of cells

1) simple organic molecules such as amino acids and hydrocarbon chains were formed
2) catalysis
3) larger organic molecules including RNA and phospholipids were formed from smaller molecules
4) RNA able to self-replicate
5) compartmentalisation: formation of a cell membrane, allowing it to have a different internal chemistry than the outside

Formation of Vesciles

- formed of fatty acids
- when a few lipid molecules are placed in water, they from a monolayer on the surface
- if there are enough, they form bilayers
- these bilayers spontaneously form small vesicles, which are enclosed and possibly formed the membrane of early cells

spherical bilayer: double layer of phospholipids

RNA as the first cell

- RNA can assemble spontaneously from nucleotides
- RNA can replicate itself
- RNA can control the rate of chemical reactions/catalysis

LUCA

Last Universal Common Ancestor

- A simple, single celled, prokaryote, likely with an RNA genome, that existed 2.5-3.5 billion years ago

Evidence for LUCA

All living organisms we know have...
1) same biochemistry in all organisms
2) same DNA base and genetic code
3) same shared amino acids forming protein molecules

Hydrothermal vents

- scientists have found fossilised structures in the rocks
- presence of carbonate = oxidation may haver occurred

LUCA:
1) anaerobic = able to survive in the absence of oxygen
2) converted carbon dioxide into glucose
3) converted nitrogen into ammonia
4) survived in high temperatures