Origins of Cells - Higher Level Lecture Notes

Introduction

• Understanding the origin of cells involves understanding the origin of complex molecules like proteins and nucleic acids.
• Travel back to prebiotic Earth to understand the formation of these molecules.

Prebiotic Earth

• Characteristics:
  • Very little oxygen, lots of methane, high temperatures.
  • High levels of carbon dioxide, no atmosphere, intense UV radiation.
  • Frequent lightning; ideal for spontaneous generation of complex carbon compounds.
• Life on Earth altered the environment, producing oxygen, forming the ozone layer.

Definition of a Cell

• Cells are self-sustaining, using energy to maintain order and compartmentalization.
• Cells are the smallest unit of life:
  • Use energy for compartmentalization.
  • Capable of producing more cells.
  • Can live outside the body in culture.

Spontaneous Generation

• The idea that living things can spontaneously generate from non-living matter.
• Falsified by Pasteur's experiments.
• New cells come only from existing cells.

Formation of the First Cell

• Requirements for the first cell:
  • Control over chemical reactions (metabolism).
  • Self-assembly of polymers (e.g., amino acids forming proteins).
  • Compartmentalization to separate from the environment.
  • Presence of self-replicating molecules.

Miller-Urey Experiment

• Simulated prebiotic Earth conditions to produce amino acids.
• Supported the hypothesis that carbon compounds arose before life.

Compartmentalization and Vesicles

• Phospholipids form bilayers spontaneously in watery environments.
• Phospholipid bilayers are semi-permeable, aiding compartmentalization.

RNA as the First Genetic Material

• RNA is self-replicating and can act as a catalyst.
• Some viruses contain only RNA, indicating RNA's potential role in early cells.
• RNA mutates quicker, allowing more genetic diversity and evolution.

Common Ancestry and LUCA

• Despite differences, organisms like trees, dogs, and horses share common DNA.
• Last Universal Common Ancestor (LUCA) theory:
  • Explains universal genetic code.
  • Suggests all life descends from a single ancestor.

Dating the Origin of Life

• Carbon Dating:
  • Uses carbon isotopes to estimate time.
  • Suggests life arose ~4.1 billion years ago.
• Genomic Differences:
  • Measures genetic differences to estimate time since common ancestor.
  • Suggests LUCA formed ~4.5 billion years ago.

Likely Environment for LUCA

• Hydrothermal vents (white smokers) with conditions suitable for life formation.
• Common genes suggest the ancestor lived in anaerobic, hydrogen-rich environments.

Conclusion

• Debate remains over exact timelines and conditions.
• Biology continues to seek data to support or falsify theories.