Different DNA

Got serious doubts about the double helix DNA theory mostly because of how the replication of chromosome is seen in the video at the end of this post.

In this video one half strand of the DNA "double helix" that has been separated from the other by the enzyme helicase is being processed by the enzymes polymerase to create a new strand. Question. Where half of the "material" added by the polymerase to create the new strand comes from? Ok let's say the cell has been firstly filled with a "soup" of pair bases that may come from the "ingestion" of nutrients by the cells?
 

Note that in the video it is said "the other strand" needs to be copied backwards and in pieces, which requires maneuvering and some sort of molecular intelligence on the part of polymerase.

According to current theories, human chromosomes' "double stranded helicoidal DNA" range in length from 51 million to 245 million base pairs of atoms. At actual size, an average human cell chromosome totals up to 3 meters long and a few angstroms (10 to minus 10 meters) wide, made of two very long strings (strands) of atoms linked together as pairs. The longest known molecule that needs to stay, together many others, inside a cell.

To replicate, each double helix has to unwind and separate in two strands and each strand of course has to stay in one piece. Each strand then acts as a template for a new strand or its new pair that needs to be packed back together. But at least at a certain moment when it is unpacked, it should be indeed an "unmanageable tangle".

"Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle."

However there is a phase in cellular mitosis (division) when, before replication, chromosomes need to be unpackaged in order to be separated in the two strands by the helicase and immediately turned in two DNA helixes by the polymerase needed for the two cells after division.

How do they manage to remain a "manageable tangle" during that period?

And who or what is doing the job of unpacking/packing, scaffolding, etc..?

If you take a look at the picture below you'll see the 5 levels of winding or packaging of the DNA. At least at three different levels the DNA is packed with different types of "fiber".

http://www.bio.miami.edu/dana/pix/eukchromosome.jpg

Chromosomes are visible under microscope. Here is a video showing the very moment of the separation of the chromosomes during the mitosis (dividing) of one cell.

Let's say the two enzymes move from one end to the other of the strand without unpackaging the chromosome like seen in the video below where no unpackaging/packaging, unwinding/rewinding etc. of the double helix strands is apparent.

If the two enzymes can travel from one end to another without unpackaging, the final resulting chromosomes cannot be separated.

This video (animation) catches and earlier phase, "condensation" but still no replication. Condensation appears to be the last level of packaging as in the image above.