Biodiversity

Earth's, and Life's, Origins

• Creation of planet Earth: 4.5 billion years ago
• Origin of life: between 4 and 3.5 billion years ago

Life: Ingredients Needed

• Organic molecules (the molecules of living organisms):
  • Proteins
  • Polysaccharides (sugars)
  • Lipids (fats)
  • Nucleic acids (RNA and DNA)
• A place for these molecules to react: the cell
• A way to reproduce: RNA and DNA
• Plenty of time: this allows evolution to occur

Abiotic Synthesis

A Hypothesis for the Origin of Life

• First proposed in the 1920s by two scientists, independently:
  • A.I. Oparin (Russian)
  • J.B.S. Haldane (British)
• This would be possible because there was no oxygen to attack chemical bonds: Earth had a “reducing” atmosphere.

Miller–Urey Experiment is Successful

• Date: 1953
• Scientists:
  • Stanley Miller
  • Harold Urey
• Ingredients:
  • H₂O
  • H₂
  • CH₄ (methane)
  • NH₃(ammonia)
• Conditions: one week of electrical sparks
• Results from this and many similar experiments:
  • All twenty amino acids produced.
  • The nitrogenous bases in RNA and DNA
  • Sugars
  • Lipids

Figure 26.4, page 494, Campbell's Biology, 5th Edition

The First Polymers are Formed

• A polymer is a “chain” of simple molecules linked together.
  • Like pearls on a necklace
  • Like trains cars on a train
• Almost all important biological molecules are polymers:
  • Proteins
  • RNA
  • DNA
  • Polysaccharides (sugars)
• Sidney Fox created the first polymers abiotically.
  • They were proteins, called proteinoids (visual analogy for their polymerness: P-R-O-T-E-I-N-O-I-D-S).
  • He did not use any living processes to do this.
  • This was done by dropping organic monomers onto hot clay, sand, or rock.

From Protobionts to Cells: The Search for a Quiet Place to React

• The idea:
  • A place is needed, “away from the maddening storm,” for organic molecules to react.
  • “Divide and conquer”: the building of anything great starts with small individual pieces.
• The first step: protobionts, precursors to cells, help provide a stable and isolated chemical environment.
  • Coacervate: a spontaneously forming stable droplet formed from the mixture of organic molecules (polypeptides, nucleic acids, and polysaccharides)
• Eventually, true cells evolve, surrounded by a lipid bilayer.

Early Reproduction: RNA World

• Current Hypothesis: the first molecule capable of reproducing and carrying genetic information was RNA.
• Why RNA?
  • It is simpler than DNA: single stranded rather than double stranded.
  • It is able to self-replicate: RNA has been shown to reproduce itself under experimental conditions.
  • It is able to catalyze reactions: RNA capable of catalysis is called a ribozyme.
    • This was discovered by Thomas Cech.
    • Since it can catalyze reactions it should, in theory, be able to make proteins from its own RNA code.