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Answer to the Friday Whatsit for January 21, 2011

January 24, 2011

Everyone must have been too absorbed in the NFC and/or AFC Championship game(s) this weekend because there were no correct guesses this week.

What is it?

What is it?

My lovely neighbor’s husband is the closest, with “mitochondrial inner membrane pore.” These do exist, although they are too small for light microscopy to see accurately with anything but the most advanced technology.  But seeing as how the mitochondria are actually organelles and the other things that were guessed were funny, but not so much with the being organelles.  .  .    we’re giving it to Dr. M.

The correct answer is microtubules, micro meaning really small and tubules meaning tubes.  Really small tubes.  No joke.  They are part of the cell cytoskeleton, or the skeleton of the cell.  Again with the not joking.  Cytoskeletal elements (microtubules, actin and microfilaments) do the same thing for the cell that your bones and muscles do for you; holding shape and making movement possible.

Microtubules are made of two main proteins, alpha and beta tubulin.  The alpha/beta tubulin subunits bind together to form a tube shape that always grows from one end and dissolves from the other.  Microtubules are dynamic elements, always growing and dissolving so that the pattern of microtubule coverage in a cell changes over time.  The green color here comes from labeling with antibodies to the beta tubulin protein.

Microtubules have three main jobs (that we know of): 1) bind into bundles to form cilia and flagella, those wonderful bits that allow sperm and organisms like bacteria to move, and aid in things like sweeping mucus out of your lungs and absorbing nutrients in the intestine  2) attach to the chromosomes during cell division and help pull them apart into the two daughter cells and 3) act as highways for transporting stuff around the cell in big balloons of membrane called vesicles.  Interestingly, the vesicles don’t appear to travel inside the tube, although it is hollow.  Instead, the microtubules act as scaffolds for motor proteins called kinesins and dyneins.  These motor proteins look like strings with giant Mickey Mouse feet on the end, only the feet are actually called heads.  The heads bind to the microtubule and walk down the tube carrying the vesicle cargo with its tail end sticking up above the tubule (see an animation in the Inner Life of the Cell video at about 1:07).  I saw a video of an actual motor protein moving down an actual microtubule recently, and if I can find the video outside of a journal pay wall, I will post it for you.

Tune in on Friday when Whatsit returns to the kitchen for inspiration. . .

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