Origin of cells

• Conditions on early earth

  • Ammonia
  • Methane
  • Water vapor
  • Hydrogen
  • Temperatures exceeding 100
  • Only ocean, no solid land
  • Comets + asteroids brought water + other compounds
  • Has more water and carbon dioxide
  • No ozone layer
  • Solid inner core
  • Smaller protective magnetic core
  • More cosmic and solar radiation
  • Extreme weather events and storms
  • Ultraviolet light penetration
• Cells


  • Smallest unit of self-sustaining life
  • Metabolism
  • Response to stimuli
  • Homoeostasis
  • Movement
  • Growth
  • Reproduction
  • Excretion
  • Nutrition
• Viruses


  • Non-living
  • Unable to reproduce outside host cell
  • Rely on host for nutrition and growth
  • Do not have a metabolism
• Spontaneous origin of cells

  1. Simple organic molecules formed

  2. Chemical reactions sped up by catalysis

  3. Larger organic molecules assembled

  4. RNA could self-replicate

  5. Membrane bound compartments form
• Miller-Urey experiment


  1. Closed system

  2. Water stimulates ocean

  3. Gas inlet adds reducing gases

  4. Electric sparks to simulate electric storms

  5. Water was vaporized

  6. Condensed water droplets are like primordial soup

  7. After a week, the soup contained basic organic monomers
• Essential features for the first cells to live + evolve

  • Self replication
  • Genetic material
  • Self assembly of protein and other cell components
  • Molecules that act as enzymes
  • Compartmentalization
• LUCA


  • Simple, single celled autotroph with an RNA genome
  • 2.5-3.5 million years ago
• Evidence for LUCA


  • Genetic code shared by all living organisms and viruses
  • Same codons for the same amino acid
  • Genetic code conserved
  • Phylogenic analysis and fossils suggest it evolved in hydrothermal vents
  • Rich in hydrogen and dissolved materials for an energy source
  • anaerobic
• Estimating dates of LUCA

  • Radiometric dating
  • Genomic analysis
  • Amino acid composition
• Spontaneous formation of vesicles

  1. Fatty acids spontaneously coalesced to form a spherical bilayer

  2. Interior and exterior environment is different

  3. Cell controls conditions
• RNA as the first genetic material
• What was the methane and ammonia level on early Earth?

  Much less than previously thought
• What gases were present in lower amounts during the Miller-Urey experiment?

  Carbon dioxide and nitrogen
• What type of energy source was used in the Miller-Urey experiment?

  Electrical discharge
• How does the energy source in the Miller-Urey experiment differ from natural conditions on early Earth?

  It used electrical discharge instead of UV light