Overview
This lecture explores protocells—artificial, lifelike chemical systems—created in the lab to study the transition between non-living and living matter and their relevance to understanding the origin of life and possibilities for extraterrestrial life.
Life vs Non-life: The Continuum
- Historically, a strict divide existed between non-living and living systems, but science now sees a continuum.
- Viruses are an example of entities at the border, not fully satisfying all life characteristics.
Characteristics of Life
- Life has a body to distinguish itself from the environment.
- Life has metabolism to convert resources into building blocks for maintenance and growth.
- Life contains inheritable information (e.g., DNA or RNA) passed to offspring.
- Combining body, metabolism, and inheritable information enables replication and evolution.
Protocell Experiments
- Protocells are simplified chemical models of primitive cells with lifelike features.
- Lab protocells are created using self-assembly, starting with tens of molecules rather than millions.
- Membrane molecules and oil-water systems can self-assemble into cell-like structures.
- Example: Using montmorillonite clay and RNA to create protocells with metabolic and informational components.
Protocell Behaviors
- Some protocells use chemical metabolism to move and interact with their environment.
- Protocells can seek resources, remodel surroundings, and display collective behaviors.
- Different protocell types can fuse or "dance," showing emergent, lifelike collective phenomena.
- Hybridization of protocells may lead to new behaviors such as self-replication.
Primordial Conditions and Artificial Life
- Experiments demonstrate protocell self-assembly and lifelike behavior even from complex, messy mixtures (primordial ooze), not just pure chemicals.
- Tar-fueled protocells can move, interact, and find resources in their environment.
Defining Life and "Weird Life"
- Artificial life experiments help redefine life and expand possible forms of life.
- Criteria for life elsewhere: non-equilibrium (energy input), liquid environment, and ability to make/break chemical bonds.
- Protocells meet these criteria, suggesting life could exist in forms very different from Earth's.
Key Terms & Definitions
- Protocell — A simple, artificial chemical system designed to model primitive life.
- Self-assembly — Process where molecules spontaneously organize into larger, structured forms.
- Metabolism — Chemical processes that convert environmental resources to maintain and build structures.
- Inheritable Information — Molecular systems like DNA or RNA that carry information passed across generations.
- Non-equilibrium — A state where energy is continually supplied, preventing the system from reaching stasis.
- Weird Life — Life forms with fundamentally different chemistry or structure from what exists on Earth.
Action Items / Next Steps
- Review characteristics and requirements of life.
- Read about recent protocell artificial life experiments.
- Consider how life might be detected under "weird" or extraterrestrial conditions.