A2.1 Origins of cells Flashcards
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Functions of life
Metabolism - all chemical reactions that occur within the organism
Growth - may be limited but is always present
Excretion - chemical compounds that an organism cannot use or that may be toxic or harmful to be released from the organisms system
Reproduction - involves hereditary molecules that can be passed to the offspring
Responding - to stimuli in the environment. This is essential for the organism to survive and adapt.
Homeostasis - maintenance of a constant internal environment
Nutrition - using a source of compounds with many chemical bonds that can be broken down to provide an organism with the energy necessary to maintain life
Conditions on early earth
- Lack of free oxygen and therefore ozone
- Higher concentrations of CO2 and CH4, leading to increased UV penetration and higher temperatures
- These atmospheric conditions caused the spontaneous formation of carbon compounds that do not occur in the present
principles of cell theory
- All organisms are composed of more than one cell
- Cells are the smallest unit of life
- All cells came from pre-existing cells.
Chemical and physical processes in order for a cell to evolve
- Synthesis of small carbon-compounds from abiotic molecules e.g. Miller-Urey experiment
- Small organic molecules join to form large-chain molecules called polymers
- polymers being contained by membranes, creating a homeostatic environment around the polymers, separate from their surroundings (emergence of cell compartmentalisation)
- Development of self-replicating molecules for inheritance and control
Describe the Miller-Urey experiment
- CH4, NH3, H2, H2O represented the prebiotic atmosphere
- water used to model the ocean
- water heated to produce water vapour - rises to the chamber containing the rest of the inorganic compounds
- 2 electrodes in the chamber produce 7500 volts at 30 amperes, representing lightning
- cold water flows into the condenser to allow condensation of gaseous compounds
Strengths and limitations of Miller-Urey
Strengths:
- demonstrated that in prebiotic earth atmosphere, amino acids and other molecules can be generated spontaneously under certain conditions
- identified several organic molecules known to exist in existing organisms.
- many laboratories around the world have reproduced the experiment with similar results
Weakness:
- there is the belief that the atmosphere formed slowly over extended periods of time by the release of gases from volcanoes
- However volcanic gases today do not contain methane and ammonia
- proteins break down into individual amino acids in water
- however amino acids are not observed to join to form complex structures
- conflicts with the belief that complex molecules could form in a primordial soup environment.
Describe spontaneous formation of vesicles
- Coalescence of fatty acids into spherical bilayers:
- Fatty acids have hydrophilic and hydrophobic properties, they organise themselves into vesicles
- can engulf other organic molecules, grow and replicate,
- compartmentalisation allows specialisation of functions in diff regions.
RNA as first genetic material WHY??
- RNA can assemble spontaneously from simpler organic molecules called nucleotides
- RNA can make copies of itself, acting as a type of genetic material
- RNA has the ability to control chemical reactions
- Ribozymes in the ribosome aren still used to catalyse peptide bond formation in protein synthesis
- RNA is much simpler in structure than DNA
Evidence for LUCA
- universal genetic code carried by DNA
- over 300 shared genes, sections of DNA common
- same building blocks for DNA and RNA
- ## common molecular processes in all cells eg. DNA and RNA replication, protein synthesis
Could there have been other organisms before/during LUCA?
Yes. However they became extinct due to competition from LUCA and its descendants
Absolute dating
The process of determining an age of a specified chronology in archeology/geology
Includes: radiometric dating
Pros: high precision, determines numerical age
Cons: Expensive
Relative dating
Science of determining the relative order of past events
Includes: Biostratigraphy, stratigraphy, cross dating
Pros: less expensive, efficient
Cons: inaccurate; low precision
Evidence for evolution of LUCA near hydrothermal vents
- presence of both hydrogen and carbon dioxide = reducing environment
- Reducing environment observed to support an increasing number of bonds between carbon and hydrogen
- commonality of genetic sequences in organisms near those vents
- mineral-rich environment with both the acidic and basic fluids needed for chemical reactions
