Prebiotic earth
Conditions that living organisms need to maintain their life
metabolism,
reproduction,
sensitivity (responsiveness),
homeostasis,
excretion,
nutrition and
growth (movement)
Why viruses are considered non living?
Because they cannot carry out all life functions independently
Viruses lack metabolism and must rely on metabolic events in a host cell to generate its component parts
A virus can therefore not reproduce autonomously and must infect a cell in order to replicate
abiogenesis
The first cells must have spontaneously arisen from non-living material
Abiogenis Theory Stages
Catalysis: Simple organic molecules were synthesised from primordial inorganic molecules
Self-Assembly: More complex polymers were constructed from these simple organic molecules
Self-Replication: Certain polymers formed the capacity to be duplicated (enabling inheritance)
Compartmentalisation: These molecules became packaged into membranes with unique internal chemistry
The theory of abiogenesis has been difficult for scientists to test for a number of reasons:
The exact conditions on pre-biotic Earth no longer exist and cannot be replicated under controlled settings
The first protocells did not form fossils and so there is limited evidence on which to base hypotheses
Organic Compounds
All cells and organisms are constructed from complex carbon-based macromolecules called organic compounds
Steps of the Miller-Urey experiment
Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions
The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions)
The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week
After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules
RNA is presumed to have been the first genetic material due to two key qualities:
RNA can self replicate: RNA can form a complementary template sequence that can be used to produce new identical molecules
RNA can act as a catalyst: RNA catalysts (ribozymes) are involved in peptide bond formation and intron splicing in modern cells