A2.1 origin of cells Flashcards
conditions of early earth
- high temperatures
- regular lightning and electrical storms
- reducing atmosphere
- no free oxygen so no ozone layer
- high levels of harmful radiation due to no ozone layer
- atmospheric gases: CH4, NH3, H2, CO2, water vapour
- one global ocean with no land masses
evolution of the first cells
- inorganic compounds formed small organic molecules
- small organic molecules joined to form polymers (larger complex molecules)
- enzyme catalysis to speed up chemical reactions
- self-replication of RNA, RNA as the first genetic material
- cell membrane formation and compartmentalisation
functions of life
- Metabolism
- Reproduction
- Homeostasis
- Growth
- Response (sensitivity)
- Excretion
- Nutrition
MR H GREN
even though viruses have genetic material they are not living because they cannot carry out basic functions of life without a host
cell theory: 3 main points
- all organisms made of one or more cells
- all cells came from pre-existing cells
- cells are the smallest unit of life
miller-urey experiment
Stanley Miller and Harold Urey wanted to simulate conditions of early Earth to see if these gases could produce the first stage in the evolution of life.
- apparatus charged with simple inorganic compounds, CH4, NH3, H2 (early earth’s atmosphere)
- heat (representing high temps) to vapourise the water (sea) which traveled into the chamber of atmospheric gases.
- two electrodes producing high voltage and amps (electrical storms) created electrical sparks to trigger a chemical reaction.
- cold water running through condensor to condense the gaseous compounds from the chamber
- chemical analysis on sample collected showed that simple, organic molecules were formed (amino acids, hydroarbons)
what was the miller-urey theory about the origins of life
theory of primordial soup: life originated from a water-based sea of simple organic molecules
theory of origins of life from volcanoes
if atmospheric gases came from volcano gases on early earth then the composition would be:
- water vapour
- CO2
- sulfur dioxide
- small amounts of carbon monoxide and hydrogen sulfide
these would produce a non-reducing environment which would not allow for carbon compounds to form.
RNA as the first genetic material
RNA is thought to be the first genetic material because:
- it has the ability to self-replicate
- it is more simple than DNA (e.g single stranded)
- it has an enzymatic role because it can control chemical reactions
- it can assemble spontaneously from nucleotides
the formation of vesicles
phospholipid bilayer, when a large number of fatty acids are placed in water they display a polarty, they form vesicles: small, cell-sized double-layer bubbles. They are amphipathic molecules as they have a hydrophilic head, and hydrophobic tails. The head is made of a phosphate group, and it has two tails made up of fatty acids.
boundary around the vesicle known as compartmentalization, separates the inside of the cell from the surrounding environment. bilayer because it has two layers of phospholipids.
evidence for LUCA: last universal common ancestor
LUCA is not thought to be the first life on earth, but more as the latest common ancestor.
- universal genetic code carried by DNA
- over 300 common genes among cells
- same building blocks (amino acids) for RNA and DNA
- similar transport mechanisms
- common molecular processes within cells
methods of fossil tracing
fossils are evidence of the earliest life on Earth.
absolute dating: uses radiometric tracing using half-life. Compares isotope activity of fossil to isotope activity from when it was alive to determine its age.
relative tracing: uses sediment (layers of rock and soil) sequences to measure the age of the fossil. However, geological processes may disturb original sequence so not as accurate.
hydrothermal vents
cracks in the crust of the seabed expose water to the rock underneath, which is heated by magma. hot water rises and picks up countless minerals along the way. These high temperatures are thought to have triggered chemical reactions to form carbon compounds (another theory for the origin of life).
disproves the idea of no theory on the ocean floor due to no sunlight as tube worms exist around these hydrovents. Bacteria use minerals to make food that nourish the tube worms.
evidence to support possible appearance of LUCA and early origins of life at hydrothermal vents
- follized traces or precipitates found around hydrothermal vents
- common genetic sequences in organisms near vents, points to common ancestor
- mineral-rich environment with acidic and basic fluids, necessary environments for chemical reactions
- reducing atmosphere: high amounts of H2 and CO2 which allows for carbon compounds to form.
