Biology A2.1- origin of cells (HL version)

conditions on early earth

• lack of free oxygen

• higher concentrations of carbon dioxide and methane

• results in higher temperatures and ultraviolet light penetration

  • these conditions caused a variety of carbon compounds to form spontaneously by chemical processes that do not now occur

main components of gasses

• methane (CH4)

• ammonia (NH3)

• water vapor (H2O)

• carbon dioxide (CO2)

• hydrogen sulfide (H2S)

• hydrogen (H2)

  • nitrogen (N2)
    

describe the main components of gasses

• high temperatures at first

• frequent volcanic activity

• thunderstorms and lightning

• strong UV radiation

  • gradual cooling - resulted in spontaneous formation occurred during conditions

why are viruses considered to be non living

they cannot carry out the functions of life on their own but they can reproduce themselves

3 main principles of cell theory

1. all organisms are composed of one of more cells

2. cells are the smallest unit of life

   1. all cells come from pre-existing cells

key problems of the 3 main principles of cell theory

• non living synthesis of simple organic molecules (eg. sugars and amino acids)

• assembly of these organic molecules into polymers

• formation of polymers that can self replicate (enabling inheritance)

  • formation of membranes to package the organic molecules

evidence for the origin of carbon compounds

Miller and Urey experiment

describe miller and urey experiment

• copies conditions of early earth

• mixed gasses they thought were in the atmosphere and sealed them in a container

• added heat and electrical sparks ( lightening)

• after a week, they found amino acids

• shows how simple chemicals could form basic molecules

paradigm shift

a big change / abandoned theories due to conflicting evidence

miller and urey experiment conclusion

simple organic molecules could be created a-biotically

primordial soup

the idea that early earth had oceans full of chemicals reacting with each other by using energy from lightening to form the first organic molecules. the “soup” is where life is thought to have first begun

protocells

before cells

protobionts

before life

limitations of miller and urey experiment

• not possible to say the exact gasses were used

  • some scientists suggest the atmosphere was “non reducing” and composed of water vapor, sulfur dioxide, carbon monoxide

another way to look at cell origin

hydrothermal vents (black smokers)

LUCA

last universal common ancestor

- evidence:

• genetic code carried by DNA is shared by all cells

• over 300 genes / sections of DNA in common in all cells

• same building blocks for DNA and RNA within all cells

• similar transport mechanisms for cellular materials

isotopes

atom with a different number of neutrons

index fossils

• fossils of the same age that are found in strata in different parts of the world

  • all strata around the world containing the same fossils are the same age

hydrothermal vents

• hot water is beneath the ocean floor

  • no sunlight at the ocean floor but communities have been living there

    bacteria make food from minerals using the vents