Origin of Life
and Ordering Diversity
How Did Life Get Started?
Origin of Life on Earth
Oparin-Haldane Hypothesis
(1920s)
Key steps:
Stage 1. synthesis of organic molecules:
Organic molecules (amino acids, sugars, nucleotides)
essential to the formation of life could have been
made in the absence of life
Stage 2. polymerization of macromolecules
-
Spontaneous appearance of organic molecules
produced a “primordial soup” that gave rise to
living cells
Stage 3. formation of membranes
Stage 4. evolution of cellular properties
Reducing Atmosphere Hypothesis
Reducing Atmosphere Hypothesis
(1950s)
Atmosphere contained
H2
-
-
-
-
NH3
CH4
simple molecules of ancient earth participated in
chemical reactions that produced complex molecules
chemical reactions require energy
+ volcanic gases (mostly CO2, N2, and H2O)
Ancient earth - lack of ?
Why are these particular molecules of ancient
earth essential to chemical evolution?
Redox Reactions
Redox Reactions Involve a Transfer of Electrons
• reduction-oxidation reactions
• oxidation:
• reduction:
Chemical Evolution Hypothesis
Early Origin-of-Life: Miller-Urey Experiments
Extraterrestrial Hypothesis
- Evidence supporting this idea comes from study of
meteorites
- Meteorites contain substantial amounts of organic
carbon such as amino acids and nucleotide bases
Chemical Evolution Hypothesis
Simple molecules containing C, H, O, N react to form molecules with reduced
carbon atoms, which then react to form organic compounds with C-C bonds;
further reactions produce amino acids, sugars, etc.
Could these organic molecules have been destroyed by heat and collision?
Deep-Sea Vent Hypothesis
Stage 2: Formation of Organic Polymers
(1980s)
(1950s)
- Cracks in the earth’s surface release hot gases
- Synthesis of organic molecules may have occurred in
the gradient between hot and cold water
- Cannot form in water
- Likely formed in evaporating tidal pools, mud, clay
Most organisms near deep sea vents receive their energy from chemicals in the vent
Stage 3: Formation of Cell-like Structures
Protobionts and Lifelike Functions
Likely pathways:
- protobiont: first non living structures that evolved into
living cells
Requirements:
1. boundary
2. information
3. enzymatic ability
4. self-replicate
Protobionts and Lifelike Functions
2. Microsheres
- water filled vesicles surrounded by an outer layer of
protein
- formed when hot solutions of proteins are cooled
1. Coacervates
- droplets of charged polymers (carbohydrates, proteins,
nucleic acids) that form spontaneously and are
surrounded by a skin of water (proposed by Oparin)
- coacervates that contain enzymes perform metabolic
functions (eg. addition of glucose-1-phosphate
produces ?)
Protobionts and Lifelike Functions
3. Liposomes
- water filled vesicles surrounded by an outer lipid bilayer
2003 discovery
clay catalyses formation of liposomes that grow and divide
presence of RNA on clay results in liposomes that contain
RNA
Stage 4: Evolution of Cellular Characteristics
Requirements:
RNA macromolecule in protobionts
Why RNA?
1. stores info in nucleotide sequence
2. capacity for self-replication
3. enzymatic functions
Chemical selection hypothesis: when a chemical in a
mixture has advantages that result in ?
Evidence: scientists have demonstrated chemical selection in the
laboratory
Cell Theory: Organization of Life
• Robert Hooke, 1665
– discovered cells
• Anton van Leeuwenhoek, 1670s
– discovered single-celled life
• Matthias Schleiden & Theodor Schwann, 1839
– all living organisms are composed of cells
– cells are the basic units of life
• Rudolf Virchow, 1866
– all cells come from other cells
What is Life?
Properties of Life
– 1. Order and Cellular Organization
– 2. Metabolism/Energy Utilization
– 3. Regulation and Homeostasis
Properties of Life
Properties of Life
– 4. Reproduction, growth, and development
– 6. Response to stimuli/environment
– 5. Heredity
– 7. Evolve
Organization of Life
Each higher level contains novel properties not present at the
simpler level of organization
Classifying Living Organisms
• To name organisms, biologists use a multilevel grouping of
individuals called classification
• Organisms were first classified more than 2,000 years ago by
Aristotle
– Living things were either plants or animals
Carolus Linnaeus (1707-1778)
The “father” of taxonomy
• Binomial nomenclature
• Hierarchical system
of classification
kingdoms
phyla
classes
orders
families
genera
species
Classifying Living Organisms
• What is the purpose of classification?
• Provide _________ names for organisms
• Help reconstruct ___________ pathways
• Allows interpretation of _________ and _________
Common names may be confusing
Why use binomial nomenclature?
Corn
Bears
Robins
BINOMIAL NOMENCLATURE
• Two-name system, specifying the
__________ and ________
• Ursus arctos Linnaeus
What Is a Species?
• John Ray (about 1700)
Biological Species Concept
(Ernst Mayr, 1942)
– A species is a group of individuals that can ….
“Groups of actually or
potentially interbreeding
populations which are
reproductively isolated
from other such groups.”
Sterile
Comparative anatomy
Classifying organisms is based on many
lines of evidence
Developmental Stages
Behavioral Traits
Building a Family Tree
enables us to glimpse the evolutionary history of life on earth
Chromosome structure
Molecular Traits
Classifying the Diversity Life
Biological Diversity: Organization by
Cell Types
Diversity of Life
• Biologists divide all living organisms into three groups
(or domains) based on cell type:
2 fundamental cell types:
– Bacteria - prokaryotes
– Archaea - prokaryotes
– Eukarya - eukaryotes
– Prokaryotes
– Eukaryotes
Three Domain System
1.10
highest, most
inclusive taxonomic
category in the
evolutionary history
of life