origin of life

difference between mechanism and function

mechanism = HOW SOMETHING WORKS

natural philosophers, such as Harvey and Descartes recognised that life is governed by the laws of physics + chemistry, not vital forces or divine control

function = what it does

key features of living organisms

• use energy (metabolise) to grow and reproduuce to increase local order ( a localised space aka a cell/body where things are highly structured) and reduce entropy (a measure of disorder/randomness)

• posess a mechanism for encoding and transmitting information (DNA) separate from the control of metabolism, which runs the cell and processes energy

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what is the LUCA

a prokaryotic organism that all modern organisms are believed to be derived from

• is the last universal common ancestor

• scientists do not know what LUCA looks like or where it existed

molecular characteristics of life

• self replication

• self assembly (separate, individual components organise themselves into structured patterns w/o mechanical or human guidance)

• autocatolysis (chemical reaction where a product acts as a catalyst for the same reaction, so reaction speeds up over time)

• cell membranes

evidence that all life on earth has a unique LUCA (last universal common ancestor)

• All living organisms have L amino acids and D carbohydrates

• metabolic pathways used to extract energy from carbohydrates are universal across all living organisms

• universal genetic code : same codons used to code for specific amino acids

RNA world theory

• RNA World Hypothesis is a concept put forth in the 1960s by Carl Woese, Francis Crick and Leslie Orgel.

• proposes that earlier life forms may have used RNA alone for the storage of genetic material.

• RNA was the primary living substance, largely due to RNA’s ability to function as both genes and enzymes.

• RNA is capable of self-replication and could therefore have carried genetic information across generations independently. 

possible origin location of RNA

Gilbert 1986 proposed that RNA formed at rock pools/coastal environmens where precursor organic molecules were concentrated

RNA then co-opted proteins and formed cells

• Precursor organic molecules are simple chemical compounds that act as the foundational building blocks for synthesizing more complex biomolecules essential for life

How could RNA nucleotides have emerged

by funelling a prebiotic chemical soup to macromolecules via reactions, which lead to :

• reduced diversity of synthetic products (only specific shapes/types of molecules that form nucletides)

• amplification of small initial differences in abundance

• stability of biopolymers and self-assembled structures

prebiottic soup

a chaotic mixture of simple, random organic compounds before life existed in earths oceans and pools. Specific environmental conditions like UV light acted as a funnel, guiding simple compounds together into macromolecules which then became RNA

biopolymers

natural macromolecules produced by the cells of living organisms, consisting of repeating monomer units bonded together in long chains

metaboolism first theory

• life originated from white smoker hydrothermal vents, where the alkaline fluids (low electrons) from the vents met the acidic seawater (high electrons)

• this created a (natural) pH gradient across the pores of the vent, so protons (H+) and electrons moved down the proton/pH gradient

• this generated energy at the boundary between the alkaline emissions and the acidic seawater

• The flow of protons and electrons provided energy for CO2 and Hydrogen to combine into organic molecules, the building blocks of metabolism

 

metabolism first theory : reverse cycle

Many anaerobic organisms use the citric acid cycle in reverse, taking geological sources of energy like H+ ions to make organic molecules from CO2

strengths of the RNA world theory

• RNA can function as both storer of genetic info and functional catalysts, self-replicating molecule

• Satisfies the principle of parsimony by offering a simpler explanation — more logical explanation — more logical for a single type of primitive molecule to form and have self-replicating characteristics than 2 different, yet complementary molecules to spontaneously form

 

 

weaknesses of RNA world

• NASA apparently stated in a 1996 report that the “significant difficulties” that surround the RNA World concept include the chemical fragility of RNA and its narrow range of catalytic activities.

• Biochemist Harold S Bernhardt stated in a 2012 biology paper that RNA is too unstable and also possesses limited catalytic properties