Nucleosomes and conveyors

The structure of nucleosomes in chromatin has been given a very interesting analogy-

“The beads on a string” appearance:

But can this structural analogy explain the function of the nucleosome? In this post, I will show you how to imagine, what the actual function of the nucleosome is in our DNA.

For this, I want you to imagine our DNA was a conveyor belt(literally!).

A conveyor belt of information! This information from our DNA should not be accessible at all times. Essentially this information would contain the sequence for synthesizing different proteins or making regulatory RNAs from the source code (yes, DNA!). Now, the cell contains all these information-extracting enzymes (transcription factors, RNA polymerases) that can recognize openly accessible sites of DNA. It is the job of the chromatin to hide away parts of the DNA and make available only specific parts to these extractors (Euchromatin and Heterochromatin).

So how does the chromatin do that to 3 billion base pairs of DNA? Well, if you had to hide away a spot on the conveyor belt such as the one below, how would you do it?

Yes! you would, in fact, place a bag/suitcase on it. Not only that, you could place multiple bags on the entire conveyor belt. These bags are just like nucleosomes, consisting of special proteins (Histones) that can be placed onto the openly accessible conveyor (DNA). Then there can be two different types of conveyor belts. One with lots of bags: This symbolizes a restricted dna sequence to turn down the effect of certain genes(In other words the Heterochromatin).

while a rather empty one would symbolize a more accessible dna to increase the production of specific proteins.

The bags are added and removed by people. Who do the people represent?- One of the coolest enzymes in our cells- chromatin modifying enzymes, which can place these luggage-like nucleosomes along different dna sequences.