Ch15. The Origin Of Life Flashcards
4 main stages of the origin of life
- Synthesis of small organic molecules
- Joining of small molecules into macromolecules
- Origin of self-replicating molecules
- Assembly of protocells
Stage 1
Nucleotides and amino acids were produced prior to the existence of cells
- spontaneous soup
- prebiotic soup
reducing atmosphere hypothesis
early atmosphere
- water vapor, nitrogen, carbon dioxide, hydrogen gas, ammonia
the atmosphere was a reducing environment
others suggest the environment was neutral
Miller Urey experiment
Electrodes passed sparks through heated gasses, which cooled into liquids before another round of heating. The process generated organic compounds, including amino acids.
-Proved that the conditions that existed on primitive Earth were capable of leading to organic compounds
- chemicals used: Water, H2, CH4 and NH3 gases, UV Rays and electricity
Deep sea vent hypothesis
Cracks in the earth’s surface: superheated water rich in metal ions and hydrogen sulfide mixes with cold seawater.
Organic molecules may have been formed in a temperature gradient.
Stage 2
Simple molecules polymerize to form RNA
- RNA synthesis can occur spontaneously
- organic molecules formed on the surface of clay
stage 3
Origin of self-replicating molecules
- RNA first macromolecule
- Ribosomes
RNA (first macromolecule)
- store information
- capacity for self-replication
- perform enzymic functions
- It is more versatile than DNA
Ribosomes
act as a catalyst to synthesize macromolecules
- can make copies of short pieces of RNA
RNA evolution
- RNA performs two roles – DNA takes over the information storage
- RNA can serve as a template to make DNA
- Proteins have greater catalytic ability than RNA
- RNA can catalyze peptide bond formation
Stage 4
polymers enclosed by a boundary
protocells
Protocells
- Cluster of molecules surrounded by a boundary
- Chemically separate from the environment
-ex: coacervates, liposomes
1. boundary
2. information
3. enzymic function
4. self-replication
History of life on Earth
4.55 billion years ago (6,000ish years)
- Genetic Changes of Evolution
- Environmental Changes
Geological time scale
4 eons
- phanerozoic
- proterozoic
- archaean
- Hadean
eras (phnaerozoic eon)
- cenozoic
- mesozoic
- paleozoic
precambrian vs cambrian
Prokaryotes (first cell)
1.8 billion years ago
endosymbiosis theory
Oxygen boom (2)
-little oxygen at first
-began with little photosynthesizers
-evolution of cellular respiration
Evolution of Mitochondria and Chloroplasts
-Enveloped by a double membrane
-Contain free ribosomes and circular DNA molecules
-Grow and reproduce somewhat independentlyin cells
-Replicate by a splitting process similar to prokaryotes
Endosymbiosis Theory
some ancient organisms engulfed bacterial cells. rather than digesting them as food, the host cells kept them on as partners in mitochondria and chloroplasts
Cambrian explosion
535-525 million years ago
marine invertebrates, arthropods, vertebrates, rising oxygen levels
Diversification?
-hard shell in marine species to find new habitats
-increase oxygen levels
-an arms race between predator and prey
Triassic and cretaceous period
-first mammals and dinosaurs appear
-reptiles are dominant land animals
first hominins
-Sahelanthropus tchadensis dated between 6 and 7 mya
-Australopithecus afarensis “Lucy” about 3.85 and 2.95 mya
-Modern Homo sapiens about 170,000 years ago
Consequences of Continental Drift
Formation of the supercontinent Pangaea about 250 million years ago had many effects
- A deepening of ocean basins
- A reduction in shallow water habitat
- A colder and drier climate inland
