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Yet Another Argument . . .
Mar. 1st, 2012 08:26 pmSo, if you were designing an assembly line, you would logically make it so that process 1, which turns A->B, and process 2, which turns B->C, are fairly close together. If you are really good, B emerges from machine 1 right in the hopper for machine 2, like those cookie-making plants where the dough comes out of the mixer right into the cookie press. If you are the kind of person who is good at scheduling, you also make it so that all the things needed arrive where they're needed at about the same time, so instead of massive warehouses full of stuff waiting to go on the assembly line, you only need modest storage areas right at the unloading docks. In real life, there is a job, called "Industrial Designer," for the person who makes sure that plants and airports are built so everything can arrive right as it is needed, and nothing ever has to travel very far or wait very long*.
In many cells, this is sort of how it works. The DNA is transcribed into mRNA in the nucleus, and the ribosomes are waiting just outside to begin work. The endoplasmic reticulum is right there, actually physically connected to the nuclear envelope. Just outside that is the Golgi body, which does a lot of the post-translational modifications that are needed to make the protein work. All other things being equal, this is a very efficient protein-making assembly line.
Except. Neural cells can be as long as three feet (although they are long and skinny), and proteins that are needed way out at the tips are not needed near the center. So evolution designed a thing which waits until a ribosome is on an mRNA, then shouts "PAUSE!" and drags it out the edge. When that protein is needed, it can be made right there.
In theory.
In practice, the protein still needs post-translational modifications. Which means that the cell ships the mRNA-ribosome out to the ass-end of nowhere, makes a protein, ships the protein back to get modified, and then ships it out again to where it needs to be. How does this make sense? I don't know!
It is (say it with me now) Yet Another Argument Against Intelligent Design.
* Although airports tend to get clogged by bureaucracy, a good one can still have a plane off the ground every fourteen seconds during the busiest hours.
In many cells, this is sort of how it works. The DNA is transcribed into mRNA in the nucleus, and the ribosomes are waiting just outside to begin work. The endoplasmic reticulum is right there, actually physically connected to the nuclear envelope. Just outside that is the Golgi body, which does a lot of the post-translational modifications that are needed to make the protein work. All other things being equal, this is a very efficient protein-making assembly line.
Except. Neural cells can be as long as three feet (although they are long and skinny), and proteins that are needed way out at the tips are not needed near the center. So evolution designed a thing which waits until a ribosome is on an mRNA, then shouts "PAUSE!" and drags it out the edge. When that protein is needed, it can be made right there.
In theory.
In practice, the protein still needs post-translational modifications. Which means that the cell ships the mRNA-ribosome out to the ass-end of nowhere, makes a protein, ships the protein back to get modified, and then ships it out again to where it needs to be. How does this make sense? I don't know!
It is (say it with me now) Yet Another Argument Against Intelligent Design.
* Although airports tend to get clogged by bureaucracy, a good one can still have a plane off the ground every fourteen seconds during the busiest hours.
