Why don t chromatin fibers knot each other when they are wound into chromosomes?

The chromatin is tightly entangled by DNA winding around a protein octamer (a bit like a string making two turns on a ball) and rotating in this monomer and then spiraling and supercoiling, and there is also a topoisomerase helix. It's not a piece of DNA wrapped around it.

If you want to unwind under normal conditions, you need to unwind the helicase layer by layer, and the DNA duplexes do not rub against each other on smooth ground like wool. There is also an electric charge in the middle. So it's hard to tie a knot.

However, if the protein and DNA are separated by beating the mandarin duck method with hydrochloric acid when the DNA and RNA are mixed with methyl green and pyroxin, I don't know if the DNA will be confused in this case. <>

In the impression of ordinary people, it feels that the dozens of chromatin fibers are floating and entangled in the nucleus. So why don't they tie knots during their daily work and when they contract and wrap into chromosomes, is it because each chromatin occupies a relatively independent space in the nucleus?

Each interphase chromosome occupies a specific region of the nucleus, so the different chromosomes do not entangle each other. It is thought that the formation of this tissue is at least due to the attachment of some part of the chromosome to some site in the nuclear envelope or nuclear layer.

The most obvious example of chromosomal organization in the interphase nucleus is the nucleolus, which is the most visible structure of the interphase nucleus under light microscopy. Parts of chromosomes that carry ribosomal RNA genes come together here.

1.A chromatid is an x-type (i.e., two sister chromatids that are identical after replication, joined by a centromere. Chromosomes that resemble x) or the two chromosomes that make up x) are essentially chromosomes, but because the number of chromosomes is defined by the number of centromere, they can only be [two sister chromatids].

So a chromosome ( ) does not become (x) if it is not replicated, so there is no chromatid.

2.That's right. The above chromosome is shaped as x, and the dot in the middle is the centromere, and there is only one.

When this centromere is divided, it becomes two chromosomes (and , the same), and there are no chromatids, but each chromosome ( ) has a centromere at this time.

In summary, the number of chromosomes is determined by the number of centromere.

1: A chromosome is a strand, and after replication, it becomes two, which is called sister chromatids.

2: The interphase chromosomes are loose and cannot be seen without processing, let alone the silk dots.

Chromatin. It is chromosomes, because they have different morphological structures at different times, so they are divided into chromosomes and chromatin.

The chromatin is a filamentous jujube, which undergoes a highly spiral, overlapping (like.

Yarn balls. the same) became chromosomes.

Hence chromosomal (plasma).

Centromere. It's always been there.

It does not disappear or appear with the mutual conversion of chromosomes and chromatin in the mold bench.