Where did cells come from?

ARE ALL CELLS THE SAME?

History of Life on Earth• Most scientists hypothesize that life on Earth

developed through natural chemical and physical processes.

This was simulated by the

Miller-Urey Experiment

History of Life on Earth• Molecules of non-living matter reacted chemically

during the first billion years of Earth’s history.

• These chemical reactions produced simple, organic molecules.

• Energized by the sun and volcanic heat, these simple molecules formed more-complex molecules that eventually became the building blocks of the first cells.

This was simulated by the Miller-Urey Experiment

History of Life on Earth

• Scientists hypothesize that RNA was the first-self-replicating information-storage molecule.

• RNA catalyzed the assembly of the first proteins.

Inorganic molecules

RNA nucleotides

RNA macromolecules

Proteins

Self-replication

RNA molecules catalyze protein

synthesis

History of Life on Earth• Laboratory experiments

have shown that, in water, short chains of amino acids can gather into tiny droplets called microspheres.

• Scientists think the formation of microspheres was the first step to cellular organization.

The first cells to form were prokaryotes.

• Simple cells with a single ring of DNA.

• So how did complex eukaryotes come about?

Origins of the Eukaryotic Cell

• Scientists seem to think they evolved through teamwork: symbiosis

more specifically….

• Endosymbiosis where one organism lives inside another to the benefit of both

Carpenter ant w/ bacteria Blochmannia

Endosymbiotic Theory

Chloroplasts and mitochondria were originally independent prokaryotes that now live inside eukaryotic cells.

What would be the advantage to a cell to enter into this type of symbiotic relationship?

How did the evolution of complex life on Earth begin?

VID-Evolution of Complex Life

Endosymbiotic Theory

• Evidence supports that eukaryotes descended from two prokaryotic cells that joined together

Why is it hypothesized that cells acquired the mitochondria first?

Evidence for the theory:

1. Both mitochondria and chloroplasts contain their own DNA.

2. Both mitochondria and chloroplasts reproduce independently of the rest of the cell.

3. Mitochondria and chloroplasts are the same size as bacteria.

4. Both mitochondria and chloroplasts contain their own ribosomes and make their own proteins.