A2.1: Origin of Cells Flashcards
Outline the conditions that are thought to have existed on prebiotic Earth, including atmosphere, temperature, UV radiation, volcanic activity and asteroid bombardment.
- Reducing Atmosphere; CO2, CH4, NH3, H2 and very little O2
- High temperatures due to asteroid collisions
- High UV Radiation due to no ozone layer
- Volcanic eruptions releasing CO2 and H2O into the atmosphere
- Asteroid Bombardment
State what the conditions of prebiotic earth may have caused
A variety of carbon compounds to form spontaneously.
Discuss the challenges of defining matter as living or nonliving.
Life consits of:
- Physical structures of life like cells and DNA
- Physiological processes of life like growth and reproduction
Limitations:
- RBC don’t contain DNA, are they not alive?
- Aseptate fungal hyphae are not divided into individual cells, are they not alive?
- Bacteria lives within another cell and can’t reproduce outside its host, alive?
Discuss the reasons why cells are considered to be living.
They can undergo cellular processes:
- Can perform independent metabolism
- Can grow
- Can replicate themselves
Discuss the reasons why viruses are considered to be non-living.
- Not made of cells
- Do not grow
- Can’t replicate themselves
- Can’t perform independent metabolism
Outline the intermediate stages needed for the evolution of the first cells on prebiotic Earth.
- Formation of simple organic molecules from inorganic compounds
- Assembly of carbon compounds into polymers
- Formation of a polymer that can self-replicate
- Packaging of molecules into compartments
Explain 3 implications of cells being formed from preexisting cells
- we can trace the origin of all the cells in our body to the first cell; the zygote produced by fertilisation of a sperm and egg
- All cells can be traced back through billions of years of evolution to the LAST UNIVERSAL COMMON ANCESTOR of all life on Earth (LUCA)
- There must have been a first cell that arose from non-living material
Discuss the 4 limitations in testing hypotheses about the evolution of the first cells.
- Conditions were very differnt on early earth
- it is impossible to replicate with certainty the conditions that would have existed on early earth
- well-preserved fossils are rare
- Methods used to estimate dates of the first living cells have ranges of uncertainty
Outline the methodology, results and conclusion that can be drawn from Miller and Urey’s experiments into the origin of biologically relevant carbon compounds.
Methodology:
- water was boiled in a flask to represent the ocean
- Ch4, NH3, and H2 were in a flask to represent the reduced atmosphere. Sparks fired between electrodes to simulate lightning
- cooling condenser turns the stream back into liquid water which drops down into a trap where molecules produced in the reactions can settle for collection
Results:
- Carbon compounds like amino acids were formed from inorganic compounds
Conclusion:
- Carbon compounds could have spontaneously formed on prebiotic Earth
Discuss the benefits and limitations of the Miller-Urey apparatus as a model for a natural phenomena.
Benefits:
- Direct observation and experimentation of early earth is not possible thus, the use of a model is required
Limitations:
The model may be oversimplified; the model does not include every single possible variable that may have influenced the formation of carbon compounds on prebiotic earth
- Do not represent all aspects of a system as they are only as accurate as the scientific knowledge on which they are based on
Outline the cause and consequence of the spontaneous formation of membranes and vesicles by amphipathic molecules such as fatty acids and phospholipids on prebiotic Earth.
Cause:
- Fatty acids coalesce to form spherical structures called micelles - the hydrophobic fatty acid tails are tucked away from the water solvent
Consequence:
- Fatty acid micelles can form highly stable vesicles containing dissolved molecules
State what modern cells use as genetic material and what modern cells use as catalysts of metabolism
- DNA as the genetic material
- Enzyme proteins as catalysts of metabolism.
List properties of RNA that suggest it was the first genetic material.
- RNA can self-replicate
- RNA can act as catalysts for their own replication
Compare the genetic stability of RNA and DNA.
DNA replaced RNA as a more stable repository of genetic info:
- Deoxyribose in the DNA sugar-phosphate backbone makes DNA chemically more stable than chains of RNA thus, greater lengths of DNA can be maintained without breakage
- The H bonds holding together the double-helical structure of DNA add additional stability
- The use of Thymine than Uracil further enhances DNA stability as Thymine is less susceptible to mutation than Uracil and those that mutate are easier to repair
Outline the ribosomal ribozyme as a type of RNA that is still used as a catalyst.
RNA that functions as a catalyst are called Ribozymes
- The ribozyme binds to a specific substrate molecule
- The ribozyme catalyses a reaction that changes the substrate by breaking or making chemical bonds
- The ribozyme releases the product and is ready to work on another substrate molecule
