Closed 12/22 Mr F. 

Totaled 11/23 Mr F

• The mitochondrion consumes oxygen to efficiently extract energy from carbon sources like glucose, producing carbon dioxide and water in the process.
• The chloroplast consumes water and carbon dioxide as it captures energy from light and funnels it into the chemical energy of glucose, releasing oxygen in the process.

Endosymbiotic theory proposes that these organelles were once prokaryotic cells, living inside larger host cells. The prokaryotes may initially have been parasites or even an intended meal for the larger cell, somehow escaping digestion.

The Oxygen Revolution was a created a difficult obstacle to overcome for anaerobic organisms. Glycolysis was the only form of metabolism in this early environment thus being the oldest form of metabolism. Around 3.2 billions years ago, cyanobacteria became the first bacteria to utilize the light from the sun and undergo photosynthesis, giving off oxygen into the environment. Under this selective pressure, all of the organisms that could not utilize oxygen either died or had to adapt. This is where endosymbiosis come into play, which is explained in our lab. Both the mitochondria and the chloroplast are products of the developed endosymbiotic theory.

diagram of a mitochondrion 

The following are evidence on how mitochondria and plastids came from ancient endosymbiosis:

• Mitochondria and plastids are just about the same size as bacteria
• New mitocondria and plastids are formed only through a process similar to binary fussion In some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate.
• Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (in being circular in shape and in its size).
• These organelles' ribosomes are like those found in bacteria

In the 1960s, the endosymbiotic theory was proposed by Boston University biologist Lynn Margulis.  She concluded that prokaryotes and organelles relationship can best be described by the term “endo – symbiosis”. 

[Endo = "within"]

[Endocytosis = (cyto = cell) a process of 'cell eating' - cells are engulfed, but then usually digested as food....]

[Endosymbiosis = cells are engulfed, but not digested...cells live together is a mutually benefitting relationship, or symbiosis]

Her hypothesis was originally:

• 1.        mitochondria are the result of endocytosis of aerobic bacteria
• 2.       chloroplasts are the result of endocytosis of photosynthetic bacteria
• 3.       in both cases by large anaerobic bacteria who would not otherwise be able to exist in an aerobic environment.
• 4.       this arrangement became a mutually beneficial relationship for both cells (symbiotic).

Margulis' original hypothesis proposed that aerobic bacteria (that require oxygen) were ingested by anaerobic bacteria (poisoned by oxygen), and may each have had a survival advantage as long as they continued their partnership.  Each would have performed mutually benefiting functions from their symbiotic relationship.  The aerobic bacteria would have handled the toxic oxygen for the anaerobic bacteria, and the anaerobic bacteria would ingested food and protected the aerobic "symbiote”.

The result = a cell with a double-membrane bound organelle. The inner lipid bilayer would have been the bacterial cell's plasma membrane, and the outer lipid bilayer came from the cell that engulfed it.

This lady really explains the Endosymbiotic Theory and has text as well.

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_endosymbiosis.html 

          Funny shirt with the endosymbiotic theory on it.  It shows a plain and simple example of the endosymbiotic theory, with the modern day eukareote "eating" a prokareote.  Simple explanation of what it is.  (P.S.   shirt costs 29.95 online if you want one)

I found this video to be really helpful in understanding the Endosymbiotic Theory.  It's in the form of a puppet show, which makes it a little corny but it breaks the process and history down into simple steps, which makes the theory really easy to understand.