A2.1 - Origin of Cells

• High levels of CO2 and CH4 trapped heat - infrared radiation from the sun was absorbed by the large amounts of CO2 and CH4 in the atmosphere --> green house effect
• UV radiation reached the Earth's surface - UV light was not blocked or trapped, directly hit the Earth's atmosphere due to the absence of protective layers
• Lack of O2 hindered ozone formation - the absence of oxygen in the atmosphere prevented the formation of the ozone layer created harsh environment for life
• Scarcity of organic compounds - the early Earth's environment had very few organic compounds which are essential for the development of life
• All cells have 3 common features, 1. a stable, partially permeable membrane that surrounds cell, 2. genetic material that can be passed on when new cells are formed and controls the function and behavior of cell, and 3. metabolic processes that allow energy generation which enables growth and reproduction.
• Protocell - pre-cellular or cell like (example: a lipid droplet with a few molecules inside)
• Theory for origin of life: protocells evolve adaptively until they eventually acquire a genetic system (likely RNA, then DNA)
• Theory for origin of life: a genetic molecule (maybe RNA) arose suddenly, capable of replication. it was evolved by natural selection, forming genetic variants that could assemble a cell membrane and start metabolizing
• Miller - Urey Experiment: organic molecules might have arisen from the chemicals present on Earth before there was life
• Polymerization: process by which relatively small molecules (monomers) combine chemically to produces a larger molecule called a polymer
• Amphipathic: a molecule that has 2 different affinities - a polar end that is attracted to water and a nonpolar end that is repelled by it
• If a few lipid molecules are in water, they form a monolayer on the surface. With more lipids present, a bilayer forms
• Cell membranes are made from modified lipids called phospholipids which has structures with hydrophobic tails and hydrophilic heads
• Protocells formed from fatty acids. Fatty acids are very stable compounds.
• Condensation/esterfication of fatty acids with glycerol forms triglycerides which is a stabilizing membrane component
• Phosphorylation (phosphate + triglyceride) forms the simplest phospholipid
• RNA is a self replicating system and has the ability to catalyse chemical change
• RNA world: hypothesis that the earliest life forms (protocells) may have used RNA for the storage of genetic material
• Central Dogma: idea that the transfer of genetic information from DNA of the chromosome to mRNA to protein is irreversible
• Ribozymes: RNA molecule capable of acting as an enzyme (has a 3 dimensional shape that acts as an active site)
• Common Ancestor: the most recent species from which 2 or more different species have evolved
• LUCA stands for the last universal common ancestor
• LUCA is made up of bacteria (eubacteria), archaea (archaeabacteria), and eukarya (eukaryotes)
• Chemosynthesis: Inorganic molecules are oxidized to release energy. This energy is used to synthesize glucose.
• Extremophile: An organism that lives in conditions of extreme temperature, acidity, alkalinity, pressure, or chemical concentration
• Properties and functions of proteins that indicate LUCA has the following characteristics:

  • anaerobic (survived without oxygen)
  • CO2 - fixing (converted CO2 into glucose)
  • H2 - dependent (used molecular hydrogen as energy source, rather than sunlight)
  • N2 - fixing (converted nitrogen into ammonia, for subsequent synthesis of amino acids)
  • thermophilic (survived in areas of very high temp - up to 122)
• Autrophic: synthesizing glucose from simple inorganic substances, using an external source of energy