Nano Visualization - Life Inside a Cell
An animation produced by Harvard University as a tool to enhance the performance of its students in biology.
We start off of course seeing white blood cells moving through a
capillary blood vessel. Then a close up showing
cilia from the
white blood cell interacting with the cells lining the capillary wall.
We then cut to a lipid raft with some large molecules floating on a fluctuating surface. The surface is the cell membrane of the
White Blood Cell,
The molecules moving together are what they call a macro-molecular complex.
We then pull back and see a meshwork or net-looking arrangement. This is a structure just inside the
White Blood Cell wall. These protein fibers give the White Blood Cell its semi-rigid shape, and by tugging on them it is able to change its shape and move around. Much of the interior of a cell is criss-crossed by these fibers, of various sizes. By building and disassembling them, the cell is able to control its shape.
We see some shots of these fibers and larger micro-tubules self-assembling. As noted above this is a little too "choreographed" and it is a more random process. We then see one being cleaved and beginning to disassemble, and some more disassembly.
One of the more striking sequences seems to show a big blob being towed along by a sort of foot that walks along. This is a
vesicle being transported along a
microtubule. It is destined to merge with the cell wall and dump its contents outside the cell. We don't see the fusion process, but near the end we see the completion of this, as a deep well in the membrane surface flattens out, and its contents are dispersed into the intracellular medium.
The "walking" process is again a little too regular. It is thought to be much floppier than this. The front end of the "foot" flops around until it hits the right spot, where it sticks. At that point an
ATP molecule must bind (this is not shown) which drives the rear foot free of the tubule. It will then flop around itself until it sticks up front. This is a "brownian motor
(or ratchet)" which is used in many places in cells.
We see a bunch of squiggly things shooting out of holes in some surface. I believe these are messenger
RNA molecules coming out of the nucleus. The nucleus creates these molecules based on the genes which are inside the nucleus, and they go out into the cells where they serve as a guide to construct proteins.
That's what we see next, a greenish blob, the
ribosome, slides along the messenger RNA and out the side of it comes a squiggly, new protein. What is not shown here is that there are millions of interactions with
amino acids that are used to build the protein.
Many ribosomes are free floating as shown here but many are also attached to what is called the
a membrane within the cell that has a complicated shape. That's what we see
next, a ribosome going down and attaching to the endoplasmic reticulum where it continues to work, producing a protein, then it detaches and separates into its two constituent pieces.
Next we see our friend the vesicle being towed along, and then a blobby, somewhat cylindrical object comes into view. Look close and you will see free-floating blobs moving through it. This big thing is a
Golgi body, and its purpose is to prepare protein products for excretion from the cell. The vesicles move through it and some kind of last minute chemical processing is done (this is not shown, I'm not sure it is understood very well what happens there).
Back to a brief shot of the towed vesicle and then suddenly we see the end of its merging process, the volcanic upwelling as the
vesicle completes its attachment to the cell membrane and finishes disgorging its contents.
Presumably this is some kind of signal the White Blood Cell is sending to neighboring cells, perhaps to prepare them for its entry.
We are back on the surface now, and see some molecules on the White Blood Cell link up to molecules on the adjacent cells. This is meant to represent the first steps by which the
White Blood Cell "grabs hold" and is able to pull itself into the gap between the cells. That's how the movie ends, with the
White Blood Cell disappearing into the body. More info and discussions at
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