Transcript Origins of Life

The Origin and Diversity of Life
Biodiversity
• ~1.5 Million species identified
• Many more remain to be identified
Possible origin(s) of life on earth?
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Extraterrestrial aliens brought it
Came with meteors from other planets
Divine creator
Chemicals from primordial soup combined
None of the above
Review of what have we learned
• Cell theory
– All living organisms are made of cells, and all living
cells come from other living cells.
• Molecular basis of inheritance
– DNA encodes genes which make-up and control
living organisms.
• Evolutionary change
– Life-forms have evolved varying characteristics to
adapt to varied environments.
• Evolutionary conservation
– Some characteristics of earlier organisms are
preserved and passed on to future generations.
Fundamental Properties of Life
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Cellular organization
Sensitivity
Growth
Development
Reproduction
Regulation
Homeostasis
Heredity
Evolution
Where did the first cell come from?
• Or….Can life arise from non-life?
• Can we test this scientifically?
– Conditions on early earth
– Formation of organic molecules
– Chemical evolution
– Primitive cell
– Prokaryotes
– Eukaryotes
– Multicellular organisms
Origins of Life
• The Earth formed as a hot mass of molten rock about
4.5 billion years ago (BYA)
– As it cooled, chemically-rich oceans were formed
from water condensation
• Life arose spontaneously
– Ocean’s edge, hydrothermal deep-sea vents, or
elsewhere
Conditions on Early Earth
• Seems likely that Earth’s first organisms emerged and
lived at very high temperatures
• First organisms emerged between 3.8 and 2.5 BYA
• Early atmosphere composition not agreed on
– May have been a reducing atmosphere
– Would have made it easier to form carbon-rich
molecules
Miller and Urey Experiment
• Reproduced early atmosphere
– Assembled reducing atmosphere rich in hydrogen
with no oxygen gas
– Atmosphere placed over liquid water
– Temperature below 100ºC
– Simulate lightning with sparks
What Was Found?
• Found within a week that methane gas (CH4)
converted into other simple carbon compounds
– Compounds combined to form simple molecules and
then more complex molecules
• Later experiments produced more than 30 carbon
compounds including amino acids and nucleotides
Chemical Evolution
• If life originally arose from non-life, how might this
have happened?
• Consider the following scenario
• Synthesis and accumulation of small organic
molecules
• Joining of these monomers into polymers
• Aggregation of these molecules into droplets to
form localized microenvironments
• Origin of heredity
Polymer Formation
• Sidney Fox (University of Miami) demonstrated the
abiotic polymerization of organic monomers
• Polymers were formed when dilute solutions of
organic molecules were dripped onto hot sand, clay, or
rock
• “Proteinoids”
• Clay can serve to concentrate these molecules
• Monomers bind to charged sites on clay particles
• Metal ions in clay have catalytic function
Which came first?
DNA
(Information)
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RNA
(Information and Catalytic)
A. DNA
B. RNA
C. Protein
Most Likely
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PROTEIN
(Catalytic and Structural)
Probable Scenario
• RNA may have been first genetic material
– Ribozyme activity
• Amino acids polymerized into proteins
• Metabolic pathways emerged
– Primitive organisms may have been autotrophic –
built what they needed
• Lipid bubbles could increase the probability of
metabolic reactions
– Leads to cell membranes
• Other innovations contributed to diversity of life
Classification of Organisms
• More than 2000 years ago, Aristotle divided living
things into animals and plants
• Later, basic units were called genera
– Felis (cats) and Equus (horses)
• In the 1750s, Carolus Linnaeus instituted the use of
two-part names, or binomials
– Apis mellifera the European honeybee
– Genus name capitalized, all in italics
Taxonomy
• Taxonomy is the science of classifying living things
– A classification level is called a taxon
• Scientific names avoid the confusion caused by
common names
The Linnaean Hierarchy
• Taxa are based on shared characteristics
– Domain → → → Species
• Early taxonomists not aware of distinction between
derived and ancestral traits
– Many hierarchies now being re-examined
• Categories at the different levels may include many, a
few, or only one taxon
• Limitations
– Many higher ranks are not monophyletic
– Linnaean ranks not equivalent in any meaningful
way
Domain
Bacteria
(Bacteria)
Domain
Archaea
(Archaebacteria)
Common Ancestor
• 3 domain system
– Domain Archaea
– Domain Bacteria
– Domain Eukarya
Domain
Eukarya
(Eukaryotes)
Grouping Organisms
Carl Woese proposed a 6-kingdom system
• 4 eukaryotic kingdoms
• Plantae
Each fundamentally different
• Fungi
• Animalia
• Protista – did not fit into 3 other kingdoms
– 2 prokaryotic kingdoms
• Archaea
• Bacteria
• Tree based on rRNA analysis
• Archaea and Eukarya are more closely related to
each other than to bacteria
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Prokaryotes
Eukaryotes
Bacteria
• Most abundant organisms on Earth
• Key roles in biosphere
– Extract nitrogen from the air, and recycle carbon and
sulfur
– Perform much of the world’s photosynthesis
• Responsible for many forms of disease
• Highly diverse
• Most taxonomists recognize 12–15 different groups
Archaea
• Shared characteristics
– Cell walls lack peptidoglycan (found in bacteria)
– Membrane lipids are different from all other
organisms
– Distinct rRNA sequences
• Divided into three general categories
– Methanogens
– Extremophiles
– Nonextreme archaea
Archaea
• Methanogens
– Use H2 to reduce CO2 to CH4
– Strict anaerobes that live in swamps and guts
• Extremophiles
– Thermophiles – High temperatures (60–80ºC)
– Halophiles – High salt
– Acidophiles – Low pH (pH = 0.7)
Eukarya
• Prokaryotes ruled the earth for at least one billion
years
• Eukaryotes appeared about 2.5 BYA
• Their structure and function allowed multicellular life to
evolve
• Eukaryotes have a complex cell organization
– Extensive endomembrane system divides the cell
into functional compartments
Mitochondria and Chloroplasts
• Mitochondria and chloroplasts most likely gained entry
by endosymbiosis
• Mitochondria were derived from purple nonsulfur
bacteria
• Chloroplasts from cyanobacteria
Archaebacteria
Animalia
Fungi
Protista
Plantae
Bacteria
Brown
algae
Red Green
algae algae
Photosynthetic
protists
Nonphotosynthetic
protists
Chloroplasts
Mitochondria
Ancestral
eukaryotic cell
Halophiles
Thermophiles
Methanogens
Purple
bacteria
Photosynthetic
bacteria
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Other
bacteria
Viruses
• Are literally “parasitic” chemicals
– DNA or RNA wrapped in protein
• Cannot reproduce on their own
• Not considered alive – cannot be placed in a kingdom
• Viewed as detached fragments of a genome
• Tobacco mosaic virus (TMV) first discovered in 1933