Seven Characteristics of Life

  • Display Order
    • Arranged in a highly ordered manner
    • Cell: fundamental unit of life
  • Harness & Utilize Energy
    • Acquire energy from the environment and use it to maintain state
  • Reproduce
    • Have the ability to make more of their own kind
  • Respond to Stimuli
    • Can make adjustments to their structure, function and behavior in response to changes to external environment
  • Exhibit Homeostasis
    • Regulate internal environment so that conditions stay relatively constant
  • Growth & Development
    • Increase their size by increasing the size/number of cells
  • Evolve
    • Populations change over generations to become better adapted to the environment

The Fundamental Unit of Life

  • Cell Theory
    • All organisms are composed of one or more cells
    • The cell is the smallest unit that has the properties of life
    • Cells arise only from the growth and division of preexisting cells


  • Last Universal Common Ancestor
  • Evidence:
    • Lipid membranes
    • Genetic system based on DNA
    • Reproduction
    • ETC – ATP & Glucose
    • DNA to RNA to Protein transfer of information
    • Common system of protein assembly: ribosomes, mRNA, tRNA

Earliest Life

  • Stromatolites dated to 3.5 billion years ago represent the earliest fossil evidence of life
    • Layered rock that is formed when microorganisms bind articles of sediment together, forming thin sheets
    • Formed by cyanobacteria – modern – posses a sophisticated metabolism
  • Panspermia is the hypothesis that very simple forms of life are present in space and seeded the earth soon after it cooled

Stages of Prebiotic Evolution

  • So what do you need?
    • Abiotic synthesis
    • Heritable Information
    • Formation of Cells
    • Assembly of complex organic molecules from simple molecules, including protein, RNA or both
    • Aggregation of complex organic molecules inside membrane-bound protobionts

Geophysical Stage

  • Conditions On Young (Primordial) Earth
    • Chemicals: H2O, H2, CH4, NH3, H2S
    • Energy Sources: ultraviolet light, lightening
    • Reducing atmosphere
      • Allow for building up of highly reduced compounds (electrons)
  • Miller-Urey experiment demonstrated that abiotic synthesis of biologically important molecules such as amino acids, sugar, nucleotide bases, lactic, acetic, formic acid, is possible
  • 1953: Miller and Urey tested this theory and produced organic molecules from inorganic ingredients
  • Life may have evolved in deep sea vents, atmosphere or surface of earth

Chemical Stage

  • Abiotic Synthesis: organic molecules from inorganic molecules
  • No abiotic synthesis today – oxidizing environment
  • Reactants
    • Water vapor
    • Ammonia
    • Methane gas
    • Hydrogen gas
  • Conditions
    • Heating by sun
    • Cooling at night
    • Radiation from the sun
    • Energy from electrical storms
  • Results (after 1 week)
    • Aldehydes, carboxylic acids formed
    • Glycine and alanine formed
    • Amino acids
    • Sugars
    • Purines & pyrimidines


  • Chiral molecule: not superimposable on its mirror image (come in two forms)
    • Two enantiomers (optical isomers)
    • Handedness
    • Same chemical and physical properties
    • Different biological properties
  • Thalidomide
    • Used as a “morning sickness” drug in 1960s
    • Antiemetic & readily convert to the other chiral form (teratogen causing birth defects)
    • Approved in 20 European countries not in NA
    • Side effect: deformed children
  • Chirality Problem
    • Miller-Urey experiment = racemic (50% of both chiral forms mixture)
    • Biology is homochiral (only one form, no mixture)
    • L amino acids, D sugars
Energy Flow in Living Systems

Origin of Homochirality

  • Homochirality
    • Essential to the evolution of life
    • Specificity is required = one chiral form
      • Random chance
      • Extraterrestrial origin
        • Murchison meteorite
          • Contains 7 amino acids
          • 9% more L isomer (bias led to life)

Biological Stage

  • Development of DNA, RNA and protein triad
  • Synthesis of polymers
  • Monomers not polymers – first cells (Miller-Urey experiment)

The Origins of Information & Metabolism

  • All organisms contain deoxyribonucleic acid (DNA)
  • DNA is copied onto ribonucleic acid (RNA)
  • RNA directs the production of protein molecules
  • Enzymes catalyze all reactions

Enter RNA World

  • RNA: information, structure, catalysis
    • Speed up rate of reaction
  • How can RNA catalyze?
    • RNA can fold
      • Complementary base pairing
    • Ribosome
      • Ancient organelle – required for all cells
      • 2/3 RNA, 1/3 protein
  • Ribozymes
    • RNA molecule that has catalytic properties
      • Self-splicing introns – catalyze own excision
      • Can catalyze reactions on the precursor RNA molecules that lead to their own synthesis, as well as on unrelated RNA molecules
    • Ribosome aminotroinferase activity
    • Can fold into very specific shapes and are single-stranded
    • Function depends on folding
    • RNA was the first molecule from which both DNA and proteins developed
    • Ribosome aminotransferase activity

Evolution of Information Transfer

  • RNA
    • Information, catalysis & structure
  • Proteins
    • Structure & catalysts
    • Diversity (20 amino acids)
  • DNA
    • DNA is more stable than RNA
      • Deoxyribose more stable then ribose
    • Base uracil found in RNA is not found in DNA; replaced by thymine – common mutation in DNA is the conversion of cytosine into uracil – by utilizing thymine in DNA, any uracil is easily recognized as a damaged cytosine and can be repaired
    • DNA is double-stranded – complementary strand can be used to repair the damaged strand

The First Cells

  • Monomers -> polymers: abiotic synthesis of cell molecules
  • Hypothesis
    • Clay particles creating a surface upon which polymerization reactions could occur
      • Accelerated spontaneous reaction by clay particles (montmorillionite)
      • High surface area & charged surface
      • Charged components of the molecules are attracted to the charged surface of the clay
      • Facilitate formation of SHORT nucleotide/amino acid chain (still function and have a selective advantage)
  • Flourescent Dye Evidence
    • Purpose: how long fluorescent dye is retained in an abiotically synthesized vesicle
    • Separates biological environment from outside environment
    • Retain macromolecules inside so their concentrations are higher inside

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  • Protobionts: The First Cells
    • Abiotically produced organic molecules that are surrounded by a membrane or membrane-like structure
    • Formation allowed for an internal environment to develop that was different than external environment

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