origin of life today how did life originate? working back from today the most basic components how...
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Origin of Life
Today
How did life originate? Working back from today
The most basic components
How DNA and RNA work
Working forward from simple molecules
Bridging the gap
Debate: how easily does life arise?
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Current Life: Animals and Plants• Very complex• Many organs, tissues with specialized functions
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The Origins of Life on Earth• What is the simplest form of life today?
The cell
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Eukaryotes
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Prokaryotic Cell
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The Origins of Life on Earth
What about viruses?• Smallest form of “life” – if considered life• Genetic material is DNA or RNA
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Prions
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The Origins of Life on Earth
• And herein lies the rub…. Viruses and Prions are dependent on hijacking the DNA of the host cell to reproduce..
• Which is the chicken and which is the egg…
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Sizes of Organisms
• Smallest eukaryote: 10^ 11atoms• Smallest prokaryote: 10^ 9 atoms• Smallest virus: 10^6 atoms• Smallest prion/viroid: 10^3 atoms
• Even smallest of these had to have smaller ancestors!
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Giant Molecular Clouds
• Amino acids
and other
• Organic Molecules
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The Origins of Life on Earth
• Miller-Urey Experiment – showed that complex
molecules can be made with simple chemical reactions
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The Origins of Life on Earth
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The Origins of Life on Earth
• Miller-Urey Experiment:
did not produce any self-replicating molecules
Today-debate about the composition of Earth’s early atmosphere
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Water
• Polar Molecule
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Phospholipids
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Cell Membrane
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What about self-replicating molecules?
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Eukaryotic Cell
• DNA contains genetic code
• Gives instructions to mRNA
• Instructions then transcribed by ribosome
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The Origins of Life on Earth
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The Origins of Life on Earth
• Proteins serve a wide variety of functions-– Best known is as enzymes
Enzymes are needed to unzip the DNA for mRNA to read
Chicken and egg?
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Gap in Understanding
• DNA- is too complicated to have been first genetic molecule
• Noted that some organisms use RNA instead.
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DNA vs RNA
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RNA in eukaryote cell• mRNA – messenger RNA is copied
from part of the DNA and contains the blueprint for a protein
• tRNA – delivers amino acids to ribosomes for building proteins
• rRNA – ribsome RNA which does the decoding of mRNA
• Ribosomes – structures of RNA and proteins which build proteins from amino acids delivered by transfer RNA
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DNA vs. RNA
• RNA can duplicate itself
• Catalyze reactions that produce subunits of RNA (more building blocks!)
• Catalyze chains of amino acids which can be used to produce proteins!
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The Origins of Life on Earth
RNA World Hypothesis:
The first genetic molecule used was RNA not DNA.
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The Origins of Life on Earth
RNA World Hypothesis:
• Hypothesis that RNA were the first self-reproducing molecules.
• They were capable of making themselves and proteins
• Later evolved to make DNA, and later evolved into DNA dominated world.
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RNA world in eukaryote cell• mRNA – messenger RNA is copied
from part of the DNA and contains the blueprint for a protein
• tRNA – delivers amino acids to ribosomes for building proteins
• rRNA – ribsome RNA which does the decoding of mRNA
• Ribosomes – structures of RNA and proteins which build proteins from amino acids delivered by transfer RNA
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The Origins of Life on Earth
What is the bare minimum for “life”?
Perhaps the first “life” included the concept of a cell….
The RNA reproduced when the soup was concentratedenough… for whatever reason….
The step to RNA is huge.
We don’t know how it happened!
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Gerald Joyce Lab
• Scripps, in CA
• Fitness of RNA, putting in only basic chemicals
• Lenski-like: let run, take out solution, put in fresh batch
• See clear improvement of
fitness
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The Origins of Life on Earth
• Working in the forward direction….• From simple molecules to life?• We know a lot about the conditions
on the Earth 4 Billion years ago. liquid watercarbon dioxidemethaneammoniahydrogenlightgeothermal energy
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The Origins of Life on Earth• Continuing extensions of the experiments with best estimates of the early Earth’s atmosphere continue at a modest level.
• Experiments can produce amino acids, sugars.• No experiment to date has produced self-replicating molecules.
• All of the chemistry is driven by the energy input in the form of “lightning” or light.
• Biological and non-biological molecules are produced in these experiments
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The Origins of Life on Earth
What is the bare minimum for “life”?
• RNA – some molecule complex enough to carry genetic blueprints for the organism.
• Cell wall – something to protect the RNA from the raw environment and contain replication
• A rich organic soup of less complex molecules to “eat”
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Nature of Cell Walls
Water is a polar molecule
Negative on one side Positive on the other
• Other polar molecules“like” water; nonpolar don’t
• Phospholipids: one water-liking side, one water hating