bubbles - possible precursors to cells
- each cell's interior differs from the exterior
- molecules w/ hydrophobic regions spontaneoulsy form bubbles in water
- edges of early oceans exposed to methane, simple organic molecules, and radiation
- primary abiogenesis - theory developed by Alexander Oparin
- early cells evolved in conditions very different from current conditions
- protobionts - early bubblelike structures that separated their contents from the environment
- idea became popular after the Urey-Miller experiment
- Lerman's bubble hypothesis - shows how organic molecules became more complex
- underwater volcanoes release gases in bubbles
- gases in bubbles react to form simple organic molecules
- bubbles pop and release contents into the air once they reach the surface
- UV rays and energy sources make the simple organic molecules form more complex molecules
- complex molecules fall back into the water and become in enclosed in bubbles
- other names for bubbles - microspheres, protocells, protobionts, micelles, liposomes, coacervates (depending on what the bubbles contain)
- coacervates - lipid bubbles that form an outer 2-layer boundary; can grow by adding more lipid molecules from the environment; can divide by pinching in 2 like bacteria
- microspheres carrying out metabolic reactions survive longer than those w/o protein or lipids inside
- bubbles better able to use the molecules/energy from the early oceans and produce offspring w/ similar characteristics would live longer
- protein microspheres - could possibly have a genetic system, do not form in water (able to form on dry land though)
- discovery of RNA enzymes >> support for idea that RNA molecules (not lipid/protein bubbles) were 1st lifeforms
microfossils - fossilized form of microscopic life
- about 1-2 micrometers in diameter
- single-celled, lacked outer appendages, similar to present-day bacteria
- prokaryotes - lack nucleus (found in eukaryotes); very simple organic body plan
- earliest records go back 2.5 billion years
- 1st eukaryotes appeared 1.5 billion years ago
archaebacteria - "ancient ones"; live in environments similar to that of early earth
- simplest organisms
- methanogens - produce methane, can't live in presence of oxygen (grows anaerobically); have DNA, lipid cell membrane, cell wall, metabolism based on ATP
- lack of peptidoglycan in their cell walls (found in other prokaryotes)
- uses strange lipid not found in any other organisms
- extreme halophiles - "salt lovers"; live in very salty environments, like the Dead Sea
- extreme thermophiles - "heat lovers"; live near volcanic vents; could be successors of earliest organisms due to ability to live w/ high heat
- DNA shows that it split from other life 2 billion years ago
bacteria - 2nd major prokaryote group; larger group than archaebacteria
- have very strong cell walls
- account for the majority of prokaryotes living today
- some can use light as energy (photosynthetic)
- cyanobacteria - aka blue-green algae; played important role in increasing the amount of oxygen/ozone in the atmosphere
eukaryotes - 1st microfossils different from prokaryotes
- all organisms other than prokarotes
- may go back 2.7 billions years, but fossil evidence only goes back 1.5 billion years
- have internal membranes and thicker cell walls
- early forms were as large as 60 micrometers in diameter
- possess internal structure called the nucleus (possibly evolved from the endoplasmic reticulum that isolated the nucleus)
- endosymbiotic bacteria - bacteria that live in other cells and perform functions for it
- theory of endosymbiosis - claims that bacteria living inside larger bacteria eventually evolved into mitochondria, chloroplasts, and other cellular parts
- developed sexual reproduction, able to frequently recombine genes
multicellularity - promoted diversity
- started when eukaryotic cells started living in colonies
- colonies began working as a single unit
- allows for specialization, giving specific tasks to certain cells
6 kingoms
- Bacteria - prokaryotic organisms w/ peptidoglycan cell wall
- Archaebacteria - prokaryotes w/o peptidoglycan in cell wall
- Protista - eukaryotic, unicellular (except for certain types of algae); can be photosynthetic/heterotrophic
- Fungi - eukaryotic, multicellular (except for yeast), heterotrophic; have chitin cell walls
- Plantae - eukaryotic, multicellular, photosynthetic
- Animalia - eukaryotic, multicellular, motile, heterotrophic
extraterrestrial life?
- at least 10% of all stars can have planetary systems
- highly unlikely that earth is the only planet w/ life
- Mars meteorite - oldest rock known to science (4.5 billion years old); contained small patches similar to microfossils and bacteria (but many times smaller)
- Europa - Jupiter's moon; most likely known place for extraterrestrial life due to liquid ocean under icy surface