The Case of the Less-than-hostile Take Over

(At the conclusion of this case you will be invited
to see something that is not there.)

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Case Studies

Although some eukaryotic organelles seem to be derived by pinching off a portion of the plasma membrane (this can be regularly observed in the formation of phagocytic vesicles in leukocytes and many one-celled organisms), there is reason to think that certain organelles have a rather different, foreign origin.

Consider some of the facts about Mitochondria:

  • consist of two membranous sacs, one inside the other;
  • have their own DNA which is more like bacterial DNA than nuclear DNA;
  • transcribe their own RNA (mRNA, tRNA, rRNA);
  • make their own ribosomes&emdash; more like those in bacteria than the RER;
  • synthesize their own proteins (including enzymes needed in the Krebs Cycle & E.T.C.);
  • divide by themselves;
  • are formed only in cells with at least one pre-existing mitochondrion.

Q:

What tentative conclusions can you make about the origin of mitochondria?

Q:

Which facts are consistent with the hypothesis that mitochondria are semi-independent or quasi-autonomous units?

Q:

Which facts are consistent with the hypothesis that mitochondria are the decendents of something phagocytized by another cell?

Q:

Which facts are consistent with the hypothesis that the phagocytized cell was something like bacteria seen today?

At the time of fertilization only the nucleus of the sperm penetrates the membrane of the ovum. It fuses eventually with the nucleus of the ovum, having left its flagellum outside&emdash;along with the mitochondrion that provided ATP for the swim.

Q:

What does this tell you about the way in which you inherit the ability to process glucose and produce ATP for every kind of work done in your body?

Q:

Will your ability to convert stored energy into kinetic energy be more like your mother's, your father's, or a combination of the two?

Q:

Which of your sixteen great-great-grandparents had mitochondria most like yours? Why do you think so?

Q:

Would your dog's mitochondria be more like the your cat's mitochondria, a wolf's mitochondria, or yours? Why do you think so?

Q:

What connections do you discern between this case and The Case of the Billion-word Essay? Ignore this question unless you've examined that case already.

Q:

How can information from Cell Biology about subcellular structures like mitochondria make a contribution to the understanding of relationships among groups of animals?

Q:

Would you like to view a movie that illustrates the ancient and current events involved in the origin and distribution of mitochondria?

Q:

Did you attempt all the items above? Click to see what is not there.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The last question in the movie asks, "What if a trivial mutation arose in a mitochondrion?"

If the answer is not intuitively apparent to you, check out the Case of the Billion-Word Essay,

in which an unrealistic analogy may provide some useful insight.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What is not here?

There are no black dots in the image.

Yet, can you see them?