here is the video from youtube
here is the narration:
so here we have a double string of nucleotide beads that spirals around itself (called the DNA double helix) like an old fashioned telephone cord. this is floating around in the cell with a negative static electric charge on it.
now proteins called histones are bumping into it. they are positvely charged and shaped just right to stick to the DNA the right distance apart and they cause the spiral to wrap up into mini spirals that bunch up into this new strand like those lanyard thingies that you probably have made.
now the supersprial spirals again into a superduper spiral
now the superduperspiral coils up yet again into a superduperduper spiral
and that makes one of your chromosomes. you have have 48 chromosomes and
here we see a cell reproducing itself by spliting in half. while it does that it has to separate out two copies of each of these 46 superduperduper chromosome twists, one for each cell.
[now your dna needs to be wrapped up this many times because in every one of your cells, the dna is 3 feet long! yet it has to fit into a cell that's a 500th of an inch wide. that's 500 cells can line up in an inch. or about 300 cells can fit into a period. imagine packing 3 feet of superfine thread into something so tiny! plus you gotta keep it from getting tangled!]
before that can happen though the chromosomes have to uncoil all that stuff and get copied! now here is the gang of of CRAZY PROTEIN machines that gang up on the DNA strand and copy it.
the double strand to be copied comes in from the left.
remember i said the DNA is TWO strands wrapped around each other. the trouble is one gets read left to right and the other gets read right to left, (they are opposites of each other) so they have to get copied in OPPOSITE DIRECTIONS. but the whole copy operation only goes forward.
so the blue machine splits the strands and unravels them, the forward reading strand goes down and gets fed into the purple and green protein machines below that add on a new strand to it to make it double again. they add the new strand from LEFT TO RIGHT AWAY from the original double strand to be copied. that's one copied DNA double helix that goes to one of the daughter cells.
the other strand that reads backwards gets sent the right through the grey/purple protein machine ahead to the right, and it gets looped around to the back and goes up and away in the picture.
the first protein machine copies the forward reading strand from left to right below, but the second purple green protein machine must copy the backwards strand from right to left but that would crash into the blue machine, so that's why the strand loops backwards first. notice that the top machine is copying in the diraction TOWARDS the original double strand. (opposite direction of the bottom copying machine, follow the strands) but it has to stay some distance away so it doesn't crash into the blue machine. anyway this will become the other double strand that gests sent to the other daughter cell.
now before we met this crazy machine, the top machine had already copied some of the backwards strand further away down the strand so now the new copying operation is going to join with the second double strand that was copied some seconds ago:
1:55 a new green machine comes in from the right because ..
the old backwards strand green machine is separating from the copied strand and the join is complete. meanwhile a new green machine has come in along with the purple machine is proceeding to make a NEW LOOP to start the whole process over agaiin.
2:08 is the closeup. the forward reading strand is to the right and the backward reading strand is coming out the top and to the left is the green/puprle machine copying the other end of that loop.
i think they make the video go too fast!