Endosymbiotic Theory EQ How were eukaryotic cells originally

Endosymbiotic Theory EQ: How were eukaryotic cells originally formed?

Evolution of Eukaryotes from Prokaryotes Eukaryotic cells arose from prokaryotes that lived in symbiosis (and eventually in the same cell).

The Mysteries of Life’s Origins

Primitive Earth Scientists believe that Earth was formed 4. 6 billion years ago as cosmic particles collided, melted and cooled. Earth was constantly in a state of catastrophe; erupting volcanoes, meteor hits and thunderstorms. The atmosphere contained very little oxygen and was made of poisonous gases. The temperature was way too hot for water to stay in liquid form, but as the Earth cooled around 3. 8 billion years ago, water fell as rain and covered most of the Earth.

The Miller–Urey Experiment 2 A mixture of methane, ammonia, and hydrogen is added to the water vapor. 1 Water is heated, and water vapor forms. 3 The circulating gases are bombarded by sparks of electricity. 4 Cold water cools the chambers, causing droplets to form. 5 After a week, liquid is collected, which contains amino acids and other organic compounds.

RNA First? Inorganic matter Simple organic molecules RNA nucleotides DNA functions in information storage and retrieval. RNA is able to replicate itself, synthesize proteins, and function in information storage. Proteins build cell structures and catalyze chemical reactions. RNA helps in protein synthesis.

ENDOSYMBIOTIC THEORY Eukaryotic cells came from a symbiosis of prokaryotic cells Prokaryotic cell that used oxygen to generate energy Prokaryotic cell that was able to photosynthesize These two cells came to live symbiotically within the same cell. EUKARYOTE I use oxygen for energy PROKARYOTE + I photosynthesize PROKARYOTE = Mitochondria Chloroplast

Origin of Eukaryotic Cells Ancient aerobic bacteria Ancient photosynthetic bacteria Nuclear envelope forming Plants and photosynthetic unicellular eukaryotes Primitive photosynthetic eukaryote Ancient anaerobic prokaryote Primitive aerobic eukaryote Mitochondrion Animals, fungi, and nonphotosynthetic unicellular eukaryotes

Life Changes the Atmosphere

Oxygen leads to endosymbiosis The primitive anaerobic bacteria were having a hard time getting energy with all the oxygen around. Newer aerobic and photosynthetic bacteria were able to get energy without a problem. Primitive anaerobic bacteria lived symbiotically with the newer bacteria, eventually internalizing them. They were the first eukaryotic organisms and showed up 2 billion years ago.

Oxygen is the best! Ah! I can’t get energy with all this oxygen around! I wish you guys could just live with me. It’d really help me out. Aerobic Bacteria Anaerobic Bacteria oxygen A few million years later… Call me chloroplast! Photosynthetic Bacteria This. Is. Awesome. Now I can get energy from my new organelles. I even have a nucleus! I’m changing my name to EUKARYOTE! Call me mitochondria!

Endosymbiotic Theory

Support for the Endosymbiotic Theory 1. Prokaryotes, mitochondria and chloroplasts have similar membranes, DNA and ribosomes. 2. All three also reproduce via binary fission (eukaryotic cells don’t). Chloroplast Prokaryote Mitochondria

Complexity in Eukaryotes

Eukaryotic Structures Krebs cycle Ribosomes Cilia and flagella Nearly all key enzymes in the Krebs cycle were borrowed from other pathways in the cell. The earliest cells may have produced proteins using RNA alone. This RNA became the ribosome; proteins were added to improve efficiency. Flagella are assembled from protein subunits that serve other purposes elsewhere in the cell.

I was once a photosynthetic prokaryote! I was once an aerobic prokaryote!

We were once aerobic prokaryotes!

Endosymbiotic Theory Another way to look at it: Video 1 And another (more fun) way to look at it: Video 2