Module 1 - Origin + Energy-Generating Systems Flashcards
What are the three main types of evidence for the earliest life on Earth?
So-called microfossils in ancient rocks
Stable isotope analysis of carbon
Fossilised stromatolites
Name the two scientists who first proposed the Primordial Soup hypothesis
Haldane and Oparin
What three main factors made the early atmosphere inhospitable to life?
High temperatures (over 100C)
Lack of liquid water
High levels of UV radiation
What is a key criticism of the Urey-Miller experiment?
The gases used did not accurately mimic the gases in the early atmosphere
Why are hydrothermal vents now considered a plausible location for the first formation of life? (3 Reasons)
There is an abundance of consistent chemical energy sources
These environments were protected from the (likely) very hostile conditions on the surface
The potential for mineral compartmentalisation in these structures
Three reasons why RNA is preferred over DNA as the hypothetical initial replicating polymer?
RNA is single-stranded and more able to fold
RNAs are known to self-replicate
RNAs can have inherent enzymatic activity
Name the 5 main “Steps/Stages” of the development of the RNA World
- Pre-biotic synthesis of RNA and proteins
- RNAs able to self-replicate
- Lipid-bound vesicles form, containing RNAs (cellular life)
- Proteins take over some catalytic functions
- (More stable) DNA evolves as the coding polymer from RNA
Name the four gases mainly present in the early atmosphere, the one key missing gas and whether the conditions were reducing or oxidising
Methane, CO2, Ammonia, Nitrogen; NO OXYGEN; reducing conditions
Describe the most likely metabolism mechanism of the first cells
A primitive membrane-bound hydrogenase enzyme spans the cell membrane;
Hydrogen acts as an electron donor, Elemental Sulphur as an electron acceptor;
A proton gradient is produced to drive ATP Synthesis via a primitive ATPase
When did the first eukaryotic cells probably appear?
Approx 1.5-2 bya
How are alignments used in modern phylogenetics?
Alignments are hypotheses as to how sequences have diverged over time (since a last common ancestor);
An algorithm can minimise mismatches by adding gaps - the more gaps required the more distantly related
Are the actual evolutionary distances generally greater or smaller than those calculated from alignment
GREATER (i.e. more distant)
The corrected distance must take into account REVERSIONS and MULTIPLE MUTATIONS AT THE SAME SITE
Name the four factors that make a gene/sequence useful for phylogenetics
- Gene present in all organisms of interest
- Not laterally transferred
- An appropriate level of sequence conservation/divergence
- Large enough to contain a record of the historical information
Which gene is generally the most useful for phylogenetics and why?
16s rRNA:
1. it contains both VERY CONSERVED and VERY DIVERSE regions (conserved regions make alignment easier, diverse regions allow closely related species to be distinguished)
2. It is part of the core translation machinery - so it has been conserved in ALL BACTERIAL SPECIES with a preserved function
What did Carl Woese propose based on RNA sequencing?
That there may be a third domain of life besides prokaryotes and eukaryotes (ARCHAEA)