The RNA World Flashcards
The RNA World
Hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins
Originally a
‘Fantasy world’
When was the RNA world?
~3.8bn years ago
Electronegativity
Ability to attract shared electrons
What is electronegativity determined by?
- atomic number
- distance of the valency shell
In what direction are the phosphodiester bonds in RNA
5’-3’
What is the direction of RNA synthesis
5’OH -> 3’OH
Purines
Guanine
Adenine
Pyrimidines
Uracil
Cytosine
Thymine
Pyrimidines are
CUTe
Why can RNA fold?
Due to free 2’OH
Examples of RNA folding
- Duplex
- Hairpin
- 90 degree kink
- Kissing loops
- Open 3 way junction
- Open 4 wag junction
- Stacked 3 way junction
- 3 way loops
Describe the tertiary structure of tRNA
- base pairing between loops folds clover into L shape
- stems stack onto each other
- impaired bases interact with each other
- variable loop induces flexibility and conformational changes
What is tertiary structure?
Folding pattern
A molecule defines life if it can
1) store information
2) adapt/mutate (evolve)
3) sense the environment
4) catalyse reactions
5) replicate itself
RNA can sense
- ions
- temperature
- pH
- salt concentrations
Riboswitches are common in
mRNAs of prokaryotes and eukaryotes
Hammerhead ribozymes can cleave
Specific RNA sequences
Where are ribozymes common
- viruses
- introns
- transposons
- all organisms
Other RNA catalysts except ribozymes
- RNA-based ligases
- RNA-based polymerases
Problem with RNA World theory
No RNA replicase has been created yet
The best RNA replicase we have so far is
A ligase that links its own precursor RNAs
Polarised bonds that have a hydrogen are a
Potential hydrogen donor
Polarised bonds that are negatively charged are a potential
Hydrogen acceptor
