Building a phenotype - RNA world

Central dogma of molecular biology

DNA transcribes to RNA which translates to protein, DNA self-replicates

RNA world theory

Hypothetical stage in evolutionary history, there were self-replicating RNA molecules before DNA and proteins evolve

Why is RNA called an acid

The phosphate can donate hydrogen ions and become negatively charged

Bases that RNA can have (and their nucleoside forms)

Adenine & adenosine, guanine & guanosine, cytosine & cytidine, uracil & uridine, and thymine & thymidine

Why could nucleotides have prebiotic origins

Phosphate is a common mineral, ribose could potentially form from formaldehyde in a formose reaction, and purines can be formed from polymerisation of cyanide

Key thing to tell which base is which when looking at chemical structure

1 or 2 carbon rings denotes purine (G and A) vs pyrimidine (U and C), and the number of hydrogens each molecule can donate/accept tells you the number of hydrogen bonds that can be formed

Which direction is RNA read and synthesised

From 5’ to 3’

Unique property of RNA (that DNA doesn’t have)

It has a 2’OH group that can both accept and donate hydrogens for hydrogen bonds, allows RNA to fold into lots of different combinations.

And the 2’OH group can bind to proteins in the various RNA functions

Does bonding have to just be between A and U, and C and G in RNA

No, for example in tRNA there are G and U base pairs

What does the variable loop do in RNA

Allows for flexibility and conformational change

What defines whether something can form life

Store information

Adapt / mutate

Sense the environment

Catalyse reactions

Replicate itself

RNA sensing the envionment

It can sense ions, temperature, pH, salt concentrations etc.

Metabolites bind to riboswitches in RNA sequence and regulate gene expression

RNA catalysing reactions

Ribozymes are enzymes based on RNA

Also have RNA-based ligases and polymerases

Can RNA replicate itself

Probably yes but no solid evidence yet. RNA-based ligase found that can link its own precursor RNAs together to create itself

What is the evidence for an RNA world

relics

What are the ‘relics’ of the RNA world

Cofactors essential for reactions and metabolism like FAD, CoA, NAD, ATP had adenosine as a base — suggesting it was a conserved element

RNA used to make proteins, is part of ribosome …?