D1 Origins of Life on Earth Flashcards

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1
Q

Describe four processes needed for the spontaneous origin of life on Earth

A

The synthesis of simple organic molecules
The assembly of these organic molecules into polymers
The formation of polymers that can self-replicate, enabling inheritance
Packaging of these molecules into membranes with an internal chemistry different from their surroundings

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2
Q

Outline the experiments of Miller and Urey into the origin of organic compounds

A
  • Miller and Urey recreated the conditions of pre-biotic Earth in a closed system
    • These conditions included a low-oxygen atmosphere, high radiation levels, high temperatures and electrical storms
    • Water was boiled to form vapour and then was mixed with methane, ammonia and hydrogen to form a reducing atmosphere
    • The mixture of gases was exposed to an electrical discharge (sparks) to simulate lightning
    • The mixture was then allowed to cool and after one week was found to contain some simple amino acids and complex oily hydrocarbons
    • Based on these findings, it was concluded that under the hypothesised conditions of pre-biotic Earth, organic molecules could be formed
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3
Q

State that comets may have delivered organic compounds to Earth

A
  • Comets contain a variety of organic molecules (~20% of a comet’s tail is comprised of organic material)
    • Heavy bombardment about 4,000 million years ago may have delivered both organic compounds and water to early Earth
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4
Q

State the conditions required for the synthesis of organic molecules

A

Organic synthesis requires the presence of a range of inorganic molecules and an energy source to combine them into organic forms

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5
Q

Discuss possible locations where conditions would have allowed for the synthesis of organic compounds

A
  • Hydrothermal vents - Regions of the ocean floor where superheated water is released from the Earth’s crust
    • Volcanoes - Intensive volcanic activity could provide sufficient thermal activity either on land or under the seabed
    • Extra-terrestrial locations - Other planets (e.g. Mars) may have been subjected to appropriate conditions (compound transfer via meteorites)
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6
Q

State two properties of RNA that would have allowed it to play a role in the origin of life

A

RNA canself-replicate

RNA can act as acatalyst

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7
Q

Outline how RNA’s self-replicating properties would have allowed it to play a role in the origin of life

A
  • One molecule can form a template for the production of another molecule, following the rules of complementary base pairing
    • Can store information in the form of a base sequence
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8
Q

Outline how RNA’s catalytic properties would have allowed it to play a role in the origin of life

A
  • Could have taken the role which is now carried out by proteins (enzymes)
    • Modern cells use RNA catalysts (called ribozymes) to remove introns from mRNA and help synthesise new RNA molecules
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9
Q

Outline the theory of protobionts as preceding living cells

A
  • Living cells may have been preceded by protobionts
    • Protobionts are aggregates of abiotically produced organic molecules surrounded by a membrane or membrane-like structure.
    • A membrane creates an internal chemical environment different to the surroundings, which could lead to optimal conditions for life activities.
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10
Q

Outline how prokaryotes to the creation of an oxygen-rich atmosphere

A
  • Primordial Earth had a reducing atmosphere that contained very low levels of oxygen gas
    • After about ~2 billion years of prokaryotic life, a form of chlorophyll evolved in prokaryotes
    • This allowed for photosynthesis to occur, creating oxygen gas as a by-product via the photolysis of water
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11
Q

Outline the result of the creation of an oxygen-rhc atmosphere ~2 billion years ago

A
  • The breakdown of chemicals in the atmosphere and oceans to produce oxidised compounds (e.g. CO2)
    • The evolution of organisms capable of performing aerobic respiration
    • The formation of an ozone layer which restricted UV radiation to allow for the proliferation of a wider range of life forms
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12
Q

Discuss the endosymbiotic theory for the origin of eukaryotes

A
  • An endosymbiont is a cell which lives inside another cell with mutual benefit
    • Eukaryotic cells are believed to have evolved from aerobic prokaryotes that were engulfed by endocytosis
    • Mitochondria and chloroplasts are suggested to have originated by endosymbiosis
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13
Q

State three pieces of evidence for the endosymbiotic theory

A
  • Mitochondria and chloroplasts have their own DNA which is naked and circular (like prokaryotes)
    • Mitochondria and chloroplasts have 70s ribosomes
    • Mitochondria and chloroplasts are roughly the same size as bacteria
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