W3L3 - Origin of Life 2 Flashcards
What does it mean for something to be “organic” (3)
- Carbon-containing
- Forms very strong covalent bonds
- Abundant
What sets carbon apart?
By latching on to many other atoms (including itself) with strong covalent bonds, it can build lipids, carbohydrates, proteins and DNA.
Properties of Silicon (3)
- Silicon has same valence
- Abundant
- Forms slightly weaker covalent bonds
What are coacervates? (4)
- Oparin-style Coacervates
- From meteorite
- Not typical cells (No phospholipid bilayer)
- Membrane vesicles, like soap bubbles, can coalesce to grow bigger or bleb
off smaller versions
How does a “cell” gets built (3)
- Put phospholipid in water
- Phospholipid vesicle forms (Hydrophobic interior)
- H2O
- Hydrophilic
- Hydrophobic
- Hydrophilic
- Exterior (H2O)
- Cell can form once something can get in the inner H2O
Evolutionary timeline of replication from simple organic compounds (6)
- Simple organic compounds (4.0bya)
- Structural organisation begins
- Development of barrier (Membrane)
- Ability to interact and maintain consistent internal environment
- Ability to transform energy into organic compounds
- Ability to replicate (3.5bya)
Can monomers in soup assemble to become macromolecules? (3)
Yes
- (1956) Heat Miller/Urey soup to 180oC for 3 hours >>> Get polymerisation of amino acids to proteinoids
- As long as starter soup ingredients are the same, we get identical protenoids
- (1959) Cool concentrated solution of proteniods >>> get microspheres
- Microspheres can divide
What are 2 assumptions behind natural selection in molecules
Assumptions:
- Molecule can replicate
- Molecules must have inheritance mechanism
What is the Selfish Gene Hypothesis (4)
- Replicators are the unit of natural selection
- Gene = Replicator
- Body = Gene’s way of making more genes
- Several genes collaborate (organism) to generate more copies of themselves
According to the selfish gene hypothesis, what are viruses?
Viruses is a gene gone maverick (independent), opted out of the consortium, selfish
In terms of hardware and software, what is RNA considered? (1)
What else can RNA be considered as? (1)
Compare the structure of DNA with RNA.(2)
- RNA is both software (contains information) and hardware (can catalyze reactions).
- It can also be an enzyme
- DNA has only one shape - double helix
- RNA can fold up like a protein (many shapes) and catalyze chemical reactions -
- *ribozyme**
What is the RNA World Hypothesis
- RNA can be an enzyme
- Catalyzes cleavage of itself (Division)
- Catalyzes rejoining of cleaved RNA
- Catalyzes peptide bond formation (protein synthesis)
- Can even catalyze own duplication!
Evidence that RNA can catalyse own duplication (3)
(2001)
- 189 base ribozyme was able to catalyse templated replication of RNA with 99.8% accuracy (Allows room for mutation)
- Only managed to copy about 20 bases (i.e. a small proportion of itself)
- Not a fully functional self-replicator
What is “Spiegelman’s Monster” experiment? (4)
Evolution in a test tube
- Simple 2-piece replicator system (Not Self-Replicating)
* Q-β RNA virus (4,500 bases) + RNA replicase protein + building blocks (bases) + ATP - Replicase makes copies of RNA with occasional mistakes
- Put them both in a tube, wait to replicate, transfer some of solution to fresh
tube with only replicase and free bases (Taking subpopulation of previous generation into a new environment) - Repeated for 54 ‘generations’and found that RNA had mutated to 218 bases (4500 > 218)
Protein > RNA in replication (2)
Why RNA is better? (3)
Protein > RNA
- Proteins offer more functional R groups to catalyze reactions than RNA (20 amino acids vs 4 bases)
- Proteins make more versatile hardware (do more jobs)
Why RNA is better
- RNA ‘learnt’ during selection to recruit proteins for replication
- In Spigelman’s monster, replicators were making copies of RNA but RNAs were mutating to give a better, more copiable version of itself
- Leads to fitter replicators (selective advantage)
- Makes sense since RNA catalyzes peptide bond synthesis in ribosome, and tRNA adapt amino acids for translation
Based on the ‘RNA World Hypothesis’, what is the role of DNA?
Does it make sense?
Role of DNA
- Double-stranded (back up or mirror copy)
- If one strand gets damaged, use other to correct
- DNA recruited as storage of information
- Very stable and safe, preserved for 1000s for years
Does it make sense?
- Makes sense because RNA is still required as a primer to initiate new DNA synthesis (end problem)
RNA/DNA, which came first? (1)
Is RNA the first? (1)
- RNA came before DNA and before proteins
- Fortuitous assembly of a self-replicating RNA is still improbable (RNA must replace an earlier simpler founder)
What are the properties of the ‘Pre-RNA’ template (4)
Slica Clays
- Mineral crystals have properties of replicators (Template, grow template, replicate)
- Take up units from environment and build into a structure
- Lack any energy system
- Lack any boundary membrane
How does RNA form from ‘Pre-RNA’ template (2)
- Silica clays form a template mould on which the RNA assembles
- Gradually RNA assumes more responsibility for self assembly, and can eventually replicate without silica template (self replicating)
TLDR: RNA World
- RNA replicator undergoing selection
- Recruited protein hardware to increase fitness
- Recruited DNA as storage of information
- Obtained a cell membrane for compartmentalisation
The road to life
- Clay replicators
- RNA replicators
- RNA/protein replicators
- DNA/RNA/protein replicators
- Cells
- Eukarya Bacteria Archaea
