A2.1 Origin of cells

HL only topic

Outline the conditions that are thought to have existed on prebiotic Earth

• lacked free oxygen and, therefore, no ozone layer, no electromagnetic shield

• comets bombarded, bringing in water and other compounds to earth.

• higher concentration of CO2 and methane

• higher temperature and ultraviolet penetration.

• had electrical storms

State how carbon compounds could’ve formed.

The environment may’ve donated electrons allowing for chemical reactions. Conditions of prebiotic Earth may have caused a variety of carbon compounds to form spontaneously

Discuss the difference between somthin that is living and somthing that isn’t. Include an explaination why viruses aren’t living.

if an organism can perform all the functions in MR. H GREN, they are living.

• movement, reproduction. homeostasis. growth, response to stimuli, excretion, and nutrition.

Viruses aren’t living because:

• can not made out of cells

• can’t maintain homeostasis

• can’t grow

• can’t reproduce

• and can’t perform metabolic reactions independently.

Outline the intermediate stages needed for the evolution of the first cells on prebiotic earth.

• formation of simple organi molecules from inorganic compunds.

• assemble of carbon compunds into polymers

• formation of polymers that can self-replicate.

• compartmentalisation with an internal chemistry that is different from the surroundings.

Discuss the limitation in testing hypotheses about the evolution of the first cells.

• Conditions on earth were very different; Its not possple to replicate with certainty.

• well preserved fossils are rare

• the method used to date first living cells have ranges of uncertainty.

Outline the methodology, result, and conclusion that can be drawn form Miller and Urey’s experiment nto the origin of biologically relevent carbon compunds.

Purpose: to investigate whether simple carbon compounds can form from inorganic compounds.

Method:

1. water is boiled till it evaporates and moves to a larger flask.

2. It combines with methane, ammonia, and hydrogen gasses. sparks are fired between electrodes to simulate lightning.

3. cool condenser turns steam into water which drips down and is collected and repeats the process.

Conclusion: carbon compounds (amino acids) were formed from inorganic compounds meaning that they could spontaneously formed on Earth.

Discuss the benefits and limitations of the miller-Urey apparatus as a model for a natural phenomena.

• modeled a hypothesized ocean-atmosphere system.

• didn’t include every possible variable that may’ve influenced the formation of carbon compounds on earth.

• it was over simplified.

• it cannot represent a system.

• only as accurate as the sciencetific knowledge it was 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.

Fatty acids, simpler phospholipids, in watery solutions will be attracted to each other and spontanously form a spherical bilayered structure called micelles= Coalesce. It tucks away the hydrophonic tails.

• allows for control over conditions to maintin homeostasis

What are the genetic material of modern cells and what are the catalysts of metabolism?

DNA - genetic material

enzyme proteins - catalysist of metabolism

List properties of RNA that suggest it was the first genetic material (RNA World)

• RNA can duplicate other RNA

• RNA can catalyze a little

• Ribozymes (RNA that functions as a catalist) in ribosomes are still used in protein synthesis.

  • It catalyzes peptide bond formation during protein synthesis.

Describe the ‘RNA first’ threory

1. RNA formed inoranically

2. replicated using ribozymes

3. catalyse protein synthesis

4. compartmentalised

5. produced protien and DNA

6. DNA took over

7. Proteins took over as enzymes

Compare the genetic stability of RNA and DNA

• DNA has a sugar phosphate backbone making chemicaly more stable. Longer DNA strands can form without breaking.

• Hydrogen bonds in the double helical structure add more stability

• DNA also uses Thymine instead of Uracil. Thymine is less likely to mutate and even if it does mutate, it is easier to repair.

Define LUCA

Last Universal Common Ancestor

Discuss why the LUCA is not thought to be the first cell, but rather is thought to be the last common ancestor to all living cells.

The first cell were likely some sort of membrane surrounding s self replicating molecule like RNA.

Explain the use of deductive reasoning to predict what genes were present in the LUCA cells.

Links the abiotic phase of the earth with traces of microbial life in rocks that is estimated to be 3.8 billion years of age.

• Molecular phylogenetics - researchers compared the gene’s genetic sequences from all 3 domains to find a shared codes. ( a total of 355 genes)

• She found a universal genetic code, a shared gene across all organisms.

List the characteristics of LUCA

• small single-celled prokaryote

• was an obligate anaerobe

• was a chemoautotroph

• was able to live in extreme heat (maybe in alkaline hydrothermal sea vents)

other life forms may’ve existed but were out-competed by LUCA

Outline the use of isotopes and the molecular clock for estimating dates of the first cells and of the LUCA cells. 

Isotopes - looks at microscopic life trapped in rocks (fossilized) and analyses the ratio of carbon isotopes. Knowing the half life of different carbon isotopes, they can get an estimate of the time.

Molecular clock - compare the difference in genomes of modern organisms to infer the existance and age of LUCA. estimated: 3.9 - 4.5 billion years ago.

Describe the conditions present at a white-smoker hydrothermal vent. 

• mineral rich water (energy and nutrient source?)

• spews at high temperatues (energy for making complex molecules

Genes for chemoautotrophic present in LUCA, environment conditions for chemoautotrophic were found in hydrothermal vents.