The First Cells
Do Now:
Read “Self-Replicating Chemicals Evolve Into Lifelike Ecosystem”
As you read, underline or highlight AT LEAST 3 portions that you think are the most interesting or
that you have a question about.
The Bakuba account of creation is as follows. Originally, the Earth was nothing but water and darkness. Mbombo, the white giant ruled over this chaos. One day, he felt a terrible pain in his stomach, and vomited the sun, the
moon, and the stars. The sun shone fiercely and water steamed up in clouds. Gradually, the dry hills appeared. Mbombo vomited again, this time the trees came out of his stomach, and animals, and people , and many other things: the first woman, the leopard, the eagle, the anvil, monkey Fumu, the first man, the firmament, medicine,
and lighting.
Is this story about where Earth, the Universe, and life began based on evidence? Can you PROVE that it’s
not true? What makes science different from other ways of understanding our world?
Origins
The Origin of Life on Earth:Abiogenesis
Evidence for a Common Origin
• DNA and RNA are the 'universal' basis for all life on Earth: all cells use RNA to make proteins.
• Only 20 amino acids are used in all living things on Earth. L-amino acids exclusively are used in all living things on Earth.
• ATP is the 'universal' energy used in all living cells.
• Fermentation (glycolysis) is the first step in ALL metabolism.
• The genetic code is almost identical in organisms as different as bacteria and humans
So when did it happen?Carbon dating techniques show that the oldest fossils are about 3.8 BILLION years old.
The oldest fossils are very similar in structure to these stromatolites - rock-like buildups of microbial communities.
Early Earth
Rocks, dust, and meteorites were pulled together by gravity to form Earth about 4.8 BYA.
The oldest rocks scientists have ever found are about 4.0 billion years old, but we think Earth was around even before that. Why aren’t there any rocks left from 4.8 to 4.0 billion years ago?
The First Organic Compounds• Complex organic molecules are common in the
universe.
• Amino acids (the building blocks of protein) can be found on comets and other moons and planets. They can even be made in the lab. They were common on early Earth.
• How organic chemicals came together to form the first cells is still under debate, but there are strong hypotheses with supporting experimental evidence.
Facts• FACT: Organic
chemicals like amino acids and proteins form cell-like spheres called microspheres and coacervates spontaneously
• FACT: RNA molecules called ribozymes can act like enzymes and catalyze reactions.
The First Cells – Archaea (prokaryotes)
Hypotheses• Many scientists believe all life
originated from an RNA molecule that had a special property – it could catalyze its own replication.
• UPDATE 2009 – SELF-REPLICATING RNA MOLECULES PRODUCED IN THE LAB!!!! “RNA WORLD” HYPOTHESIS GETS A BIG BOOST.
• Although the details are debatable, when ribozymes got into a protective fatty acid membrane, the first proto-cells arose
+
Self-Replicating Ribozymes
Coacervates & Microspheres
RNA based proto-cells
The First Cells
• The very first cells were heterotrophs, and soon used up all of the organic chemicals around them.
• The only way life could continue is if cells started to make their own chemical “food.”
CHEMOSYNTHESIS
• Proto-cells became more like cells we know today when they developed the ability to make their own carbon compounds from CO2.
• The first true cells then, were chemoautotrophs – they made food out of CO2 by using the energy in compounds like sulfur and methane.
Most Similar to The First
Life:
Archaea, a group of
prokaryotes
Endosymbiosis: origin of Eukaryotes
Key Ideas:• Earth is about 4.5 billion years old• Life (prokaryotes) arose on Earth about 3.8
BYA• Organic compounds like amino acids and
nucleotides are found all over the known universe and early Earth.
• The first cells were simple prokaryotes that were chemoheterotrophs.
• RNA was probably the first replicator molecule
