A2.1 Origins of cells Flashcards
Pre-biotic atmosphere
Less oxygen in atmosphere -> no ozone -> higher levels of ultraviolet light penetration -> Ea for chem. reactions
Higher atmospheric conc. of carbon dioxide + methane -> higher temperatures
Cells as smallest self-sustaining units of life
Living things use energy to keep themselves in a highly ordered state, making cells self-sustaining.
Cell components are not.
Origin of cells
Catalysis: Simple organic molecules were synthesised from primordial inorganic molecules.
Self-Assembly: Polymerization occured 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.
Miller-Urey experiment
- Water boiled to vapour = reflect high temps.
- Vapour mixed with gases (H2, CH4, NH3) = a reducing atmosphere (no oxygen)
- Mixture exposed to electrical discharge (simulating effects of lightning as energy source for reactions)
- Mixture cooled (concentrating components) + left for a period of ~1 week
- Condensed mixture analysed and found to contain traces of carbon compounds + amino acids
What is a vesicle?
Small droplets of fluid enclosed in a membrane. It has RNA in it and a phospholipid membrane.
Phospholipid function
Hydrophilic head group is attracted to water as it’s polar. Hydrophobic tail is non-polar. Phospholipids naturally assmble into bilayers in water -> spontaneously form spherical strutcures -> basis of vesicles.
How phospholipids/other amphipathic molecules aided in the development of cells
Membrane-bound container -> hydrophobic barrier -> allows internal chemistry of the vesicle to differ from the exterior.
(Movement of polar molecuels limited by hydrophobic membrane core)
Why is RNA the presumed first genetic material?
RNA can self replicate -> forms a complementary template sequence that can be used to produce new identical molecules
RNA can act as a catalyst
Why has RNA been superceded?
DNA has superior chemical stability (double helical structure)
Proteins are better catalysts due to greater variability (20 amino acids > 4 bases)
Genetic code
64 different codons -> each codon sequence of three bases -> codons either amino acid or a stop or start signal
LUCA
Last universal common ancestor
Genetic code universal -> same all
species, small amount of minor variations -> species use same code as they inherited it from a common ancestor
Evidence for evolution of LUCA in the vicinity of
hydrothermal vents
Genes among bacteria and archaea -> inherited common ancestor -> suggests LUCA had gene
Identified 355 protein families likely LUCA’s genome -> genes needed anerobic metabolism + fixing CO2 and N -> LUCA lived in env. of high H, CO2 + Fe conc. -> found in hydrothermal vents
Which hydrothermal vents would LUCA have thrived in?
White smokers (alkaline hydrothermal vents)-> fluids emerge at 60-90°C + contain high concs. of hydrogen, methane, ammonia and sulfides.
These chems supplied energy -> early cells needed to make carbon compounds into polymers.
CO2 needed -> present much higher quantities
