The origin of life on Earth occurred in four stages: 1) Organic molecules like nucleotides and amino acids formed spontaneously in the early reducing atmosphere of Earth. 2) These organic molecules polymerized to form RNA and proteins, which took place on clay surfaces. 3) The polymers became enclosed in membrane vesicles formed from phospholipid membranes. 4) The membrane-bound polymers acquired cellular properties through chemical selection and mutations, leading to the RNA world hypothesis where RNA carried out information storage, catalysis, and self-replication before DNA and proteins evolved.

1. Origin of Life on Earth Chapter 22 Section 1

2. Important Molecules of Life DNA Stores genetic material RNA Protein synthesis and other important roles Proteins Structure and activity of the cell

3. How they came to be . . . The origin of life occurred in four stages Stage 1 – Organic molecules were produced before cells existed Stage 2 – Polymerization of organic molecules formed polymers Stage 3 – Polymers became enclosed in membranes Stage 4 – Membrane bound polymers acquired cellular properties

4. Stage 1 Nucleotides and amino acids were created before the existence of cells It is hypothesized that these organic molecules formed spontaneously due to the conditions of early Earth The molecules formed a prebiotic soup

5. Reducing Atmosphere Hypothesis Early Earth had a reducing atmosphere Lacked oxygen Abundance in water vapor, hydrogen gas, methane, and ammonia Miller and Urey experiment

6. Extraterrestrial Hypothesis Meteorites, landing on early Earth, were abundant with organic molecules

7. Deep-Sea Vent Hypothesis Cracks in the Earth’s surface releases hot water The mixture of the hot water and the cold sea water created a gradient suitable for the formation of organic molecules

8. Stage 2 Nucleotides and amino acids were polymerized to form RNA/DNA and proteins Polymerization took place on clay Could not take place in water because hydrolysis would compete with polymerization Clay can catalyze reactions

9. Stage 3 Droplets of organic material Surrounded by a ring of water molecules Vesicles with a phospholipid membrane Coacervate Liposome

10. Stage 4 Polymers underwent mutations that changed their function Chemical Selection Polymers that had functions that were beneficial, were increased

11. RNA World It is hypothesized that the world used to be an RNA world RNA’s Key functions Information storage Enzymatic activities Self-replication RNA underwent mutations New functions

12. RNA DNA/RNA/Protein Information Storage DNA took up RNA’s ability to store information Reduced the roles of RNA DNA was created through reverse transcription Cellular Functions Proteins took up the function of catalyst and others Proteins were formed due to RNA’s ability to catalyze the formation of peptide binds