How DNA is Packaged (Basic)

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DNA packaging. Each chromosome consists of one continuous thread-like molecule of DNA coiled tightly around proteins, and contains a portion of the 6,400,000,000 basepairs (DNA building blocks) that make up your DNA. The way DNA is packaged into chromatin is a factor in how protein production is controlled.
TRANSCRIPT: In this animation we'll see the remarkable way our DNA is tightly packed up so that six feet of this long molecule fits into the microscopic nucleus of every cell. The process starts when DNA is wrapped around special protein molecules called histones. The combined loop of DNA and protein is called a nucleosome. Next the nucleosomes are packaged into a thread, which is sometimes described as "beads on a string". The end result is a fiber known as chromatin. Now the chromatin fiber is coiled into a structure called a "solenoid". This fiber is then looped and coiled yet again, leading finally to the familiar shapes known as chromosomes, which can be seen in the nucleus of dividing cells. Chromosomes are not always present. They form around the time cells divide when the two copies of the cell's DNA need to be separated. At other times, as we can see now after the cell has divided, our DNA is less highly organized. It is still wrapped up around the histones, but not coiled into chromosomes.

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DNALearningCenter

There is one mistake that could confuse students. Chromosomes are always present within the cell, but whether they are "visible" (because they are compacted) or "invisible" because they are "decondensed" does change dramatically.

This is worth clarifying because students might wonder where the DNA (and the encoded genetic information) is going when chromosomes appear to disappear.

mwklymkowsky

@DNALeaningCenter This was amazing - makes so much sense! Watching something like this is ten times better than reading this in your Biology note package. :D Thank you, DNALeaningCenter!

keesalemon