Metabolism first

Question 1

Describe 3 arguments for the ‘metabolism first’ hypothesis

Answer 1

• Metabolism is simpler than genetics and simplicity must have preceded complexity via the emergent phenomenon
• The citric acid cyle is probably a fossil for early life, its molecules are the starting points for life’s biochemistry and it also is the starting point for the synthesis of the molecular building blocks of DNA and RNA
• works well in pre-biotic environments

Question 2

What is an autocatalytic reaction?

Answer 2

A reaction which in the right environment and with enough daughter molecules will make copies and self-assemble

Question 3

What self-replicating molecule did Reza Ghadiri create?

Answer 3

A self replicating peptide of 32 amino acids, however had to be fed reactive fragments 15/17 amino acids long

Question 4

What is one key issue with self-replicating systems?

Answer 4

Can never change or evolve

Question 5

What are the pros of an autocatalytic system?

Answer 5

• molecules in a network catalyse eachother
• giving rise to complexity and a genetic mechanism is unnecessary
• an autocatalytic system is likely to change and evolve naturally

Question 6

What is the argument for first life being heterotrophic?

Answer 6

• Is much simpler, no need for complex machinery needed to make amino acids, sugars ect.
• There was a diverse set of prebiotic molecules available

Question 7

What are the arguments for first life being autotrophic?

Answer 7

• Does not depend on the resources of a local and possibly dilute environment
• chemistry emerges inevitably from geochemistry?

Question 8

Describe Sidney Fox’s protenoid world hypothesis

Answer 8

• Amino acids from the primordial soup were dried and baked on cooling volcanic rocks forming a lumpy “protenoid” substance
• Some acted like catalysts and could self-organise to form microbe sized spheres
• Environment plausible, however could not arise before a way of passing information

Question 9

Describe the main concept of Günter Wächterhäuser’s iron-sulfur world

Answer 9

• Based around the idea that first life is autotrophic and requires energy, a supply of molecules and a self-replicating cycle.
• Relies on a reverse citric-acid cycle usig H2S instead of H20 (hypothesizing that eventually would switch to H2O due to abundance)

Question 10

What are the pros and cons of the Iron-Sulfur world hypothesis?

Answer 10

Pros:
- Elaborate and testable
- Fe and Ni minerals do produce increasingly complex organics
- Many parts confirmed
Cons:
- Most researchers believe that early life is heterotrophic
- Oxyloacetate decomposes quickly to pyruvate —> acetate and some molecules use a different pathway

Question 11

What is ‘flat-life’?

Answer 11

A thin layer of chemical reactants growing on sulfide mineral and expanding laterally. Is more tolerant of high temperatures, however would be hard to detect on eath here with modern life detection techniques.

Question 12

Who proposed the ‘thioester-world’?

Answer 12

Christian de Duve

Question 13

What are thioesters and how could they make a metabolism?

Answer 13

• Molecules with strong bond between 1S and 1C
• Bond similar to phosphate in ATP
• C-S bond breaking could generate energy to drive protometabolism, also bond to amino acids to make them more active

Question 14

What are the pros and cons of the thioester world?

Answer 14

Pro: Plausible environment (volcanic with hydrogen sulfide gas and iron sulfide minerals)
Cons: Lacking detail and direction for experiments

Question 15

What reactions are involved with Günter Wächterhäuser’s iron-sulfur world?

Answer 15

First pyrrhotite reacts with common volcanic gas: FeS +H2S —> FeS2 (pyrite) + H2 + e- (energy)
which then goes on to fuel the rection H2 + Co2 —> HCOOH (formic acid)
Reactions build up essential organic molecules from CO2 and other gases.