Origins of Life Flashcards
1
Q
Formation of RNA ?
A
Long chainlike molecule that conveys genetic information and speeds up other chemical reactions
2
Q
When did DNA take over as heritable genetic material ?
A
Only later in evolutionary time
3
Q
Explain the RNA world - a very volatile place ?
A
- Volcanic eruptions shaped the early earth atmosphere:
- Thick with water vapour
- Intense UV light – no ozone
- Electrical storms
- Rich in nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen and hydrogen cyanide
4
Q
Explain Stanley Miller volcanic spark discharge experiment (1953)?
A
- Volcanic spark discharge experiment
- Abiotic synthesis of amino acids
- Darwin’s ‘warm little pond’ feasible
5
Q
Explain Stanley Miller 1953 experiment – repeated in 2008 ?
A
- After Miller’s death in 2007 several boxes found at University of Chicago
- Contained vials of dried residues from original experiments
- Re-analysed using more modern and sensitive detection systems
- 22 amino acids plus 5 amines (new amino acids underlined)
6
Q
What are the Pyrimidines ?
A
Cytosine and Uracil
7
Q
Explain the RNA formation - Pyrimidines ?
A
- Derived from precursor compounds acetylene and formaldehyde
- Undergo a sequence of chemical reactions
- Criticised because of precursor complexity
- Nucleic acid precursors created from hydrogen cyanide (HCN), hydrogen sulfide (H2S) and ultraviolet light (UV)
- Abundant on early earth – HCN from comets
- Also created natural amino acids and lipids
8
Q
What are the Purines ?
A
Adenine and Guanine
9
Q
Explain the RNA formation - Purines ?
A
- Previously found a molecule called formamidopyrimidine (FaPy) can react to form purines
- Investigated to see if FaPy could be formed in early earth conditions
- First step easy, HCN readily reacts with water to form aminopyrimidines
- Once highly reactive amines were controlled purines formed
10
Q
Explain the RNA formation – Pyrimidines and purines together ?
A
- Starting material was a plausible early earth chemical: hydroxylamine
- Cycled through wet/dry, hot/cold and acidic/basic phases to mimic varying seasons on earth in presence of phosphate containing materials
- Two separate pools that dried, rehydrated and intermixed each other
- Purines and pyrimidines formed in one-pot reactions
11
Q
RNA formation - Job done?
A
- Definitely not, much still to learn
- Not clear what reactions result in ribose sugar formation (RNA backbone)
- Not clear how A’s, G’s, C’ and U’s linked up together to form RNAs
- However, experiments at least show with the correct conditions life’s essential building blocks can be formed
12
Q
RNA acts as instruction ?
A
- Complementary base pairing enables a single RNA strand to serve as template for an exact copy
- Uracil pairs with adenine, guanine with cytosine
- This can happen in vitro (outside of usual environment)
- In this way RNA serves as an ‘instruction’
13
Q
RNA acts as as a catalyst ?
A
- Base pairing and ‘nonconventional’ hydrogen bonds allow RNA to fold into unique 3D shapes
- Determined by nucleotide sequence
- Folding permits RNA to act as an enzyme (ribozyme) for many types of chemical reactions
- Simple structure limits catalytic efficiency and scope compared with other enzymes
- Retains catalytic roles on fundamental processes in gene expression – RNA splicing/translation
14
Q
Could RNA catalyse its own replication ?
A
- Has the properties – Instruction and catalyst
- No self-replicating RNA molecules discovered in nature - Scientists working on laboratory models
- Even if demonstrated would not prove they were the origins of life - simply shows such a scenario is possible
15
Q
How does RNA predates DNA ?
A
- Ribose readily formed from formaldehyde – principle products formed from early-earth simulating experiments
- Sugar deoxyribose (DNA) harder to make
- Deoxyribose produced from ribose in reaction catalysed by enzymes
