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Flashcards in D1 Origins of Life on Earth Deck (13)
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Describe four processes needed for the spontaneous origin of life on Earth

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


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

• 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


State that comets may have delivered organic compounds to Earth

• 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


State the conditions required for the synthesis of organic molecules

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


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

• 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)


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

RNA can self-replicate
RNA can act as a catalyst


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

• 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


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

• 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


Outline the theory of protobionts as preceding living cells

• 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.


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

• 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


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

• 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


Discuss the endosymbiotic theory for the origin of eukaryotes

• 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


State three pieces of evidence for the endosymbiotic theory

• 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