Transcript Chapter 16- Origin and Evolution of Microbial Life: Prokaryotes and

Chapter 16- Origin and Evolution of
Microbial Life: Prokaryotes and
Protists
• Earth formed 4.6 billion years ago
– Early atmosphere: CO, CO2, N2, H2O, CH4,
NH3
– Very different from atmosphere today
– Lightening, volcanic activity, UV- much more
intense
• Prokaryotes- fossils date 3.5bil yrs ago
– Prevalent in mats
– Photosynthesis produces O2 in atmosphere
– Organic chemicals- 3.9bil yrs ago- possibly
from energized inorganic material (from UV or
lightening)
• Hypotheses of life’s origin
– 1- spontaneous generation- didn’t explain how
life arose in the first place (Pasteur- maggots
on meat)
– 2- comets and meteorites brought organic
compounds to Earth
– 3- (broken up into stages) 1st- synthesis of
organic molecules. 2nd- formation of polymers
from organic molecules
3rd- polymers replicate (primitive heredity). 4thpolymers aggregate having different characteristics
– Heterotroph Hypothesis- conditions of primitive
Earth produced organic substances (which could
then give rise to organisms)
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These organisms absorbed organic nutrients
Miller and Urey experiment produced amino acids
Now disproved due to change in primitive atmosphere
Now, underwater volcanoes and vents may have
provided chemical resources
• Stages in chemical evolution
– Organic molecules polymerized on hot rocks/clay
• Due to binding sites and metals that clay contained
– 1st genetic material was RNA
• Replicated itself w/o assistance
• Ribozymes- RNA that acts as enzyme, aids in splicing
and polymerization
• RNA World- hypothetical period or evolution when
RNA served as genes and catalyst molecule
– RNA could translate into protein (w/o ribosomes or
tRNA)
• Protein produced helped RNA replicate
• Lipid/protein spheres held RNA/polypeptide co-op’s
– Co-op’s grew and replicated
• Evolved a single metabolism
• Prokaryotes- bacteria
– Smaller than eukaryotes, can live in extreme
environments, live inside of us (digestive
tract), are very important.
– Come in sphere, rod and spiral shapes
– 2 groups Bacteria and Achaea
– Bacteria- found in air, land and water,
everywhere
• Covers skin, lining nose and mouth, fill
digestive tract
• Many bacteria are pathogens- disease-causing
agent
– Lyme disease, staph, meningitis, syphilis
• Koch’s postulate*
– Archaea- thrive in extreme conditions (heat,
salt, areas high in methane)
– Ways of nourishment• Photoautotroph- sun and CO2
• Chemoautotroph- inorganic compounds and
CO2
• Most prokaryotes are heterotrophs**
• Photoheterotroph- sun and organic compounds
(obtain carbon from organic molecules, E from
sun)
• Chemoheterotroph- Most abundant*- get
everything from organic compounds
– Uses of bacteria
• Biological weapons
• Recycle chemicals, clean up environment (oil spills)
• Bioremediation- use of prokaryotes to clean up
pollution
• Eukaryotes originated from communities of
prokaryotes
– Lived symbiotically (endosymbiosis)- gave rise to
mitochondria and chloroplasts
• Protists- unicellular and some multicellular
eukaryotes
– Some are photosynthetic
– Heterotrophs are called protozoa
– More complicated than prokaryotes- have
membrane bound nucleus and organelles
– 4 types:
• Protozoa- ingest food “animal like” Ex:amoeba
• Slime molds- have uni- and multi-cellular stages of life,
heterotrophs
• Unicellular algae-photosynthetic
• Multicellular algae- “seaweed”- photosynthetic
– Multicellular life probably evolved by specialization
of protist colonies
– Multicellular life- arose about 1bil yrs ago and was
aquatic until 500mil yrs ago