Video Transcript
The diagram provided shows a basic outline of how chromosomes are formed in
eukaryotes. Which letter on the diagram indicates the chromatin?
This question is asking us about chromosomes in eukaryotes. You’ll recall that eukaryotes, like humans, are characterized by the presence of a
membrane-bound nucleus to contain their DNA. In humans, if you were to unpack all the DNA inside a single nucleus, you would get
about two meters worth of DNA. How is it possible to fit all of this DNA inside a single cell?
This DNA is very compacted and organized into structures called chromosomes. In humans, there are 46 chromosomes in most cells. But it’s hard to see them individually here because they’re all mixed up
together. If we remove all but two chromosomes, we can see them a bit better.
The state that eukaryotic DNA is in when the cell is not dividing is called
chromatin. Chromatin is compacted DNA combined with special proteins called histones, which you
can see in the provided diagram on the right. However, when the cell is preparing to divide, each chromosome is copied or
duplicated as we see here. These duplicated chromosomes can become tightly coiled and condense to form a highly
compacted version of the chromosome. We can see this X-shaped structure in our provided diagram, which we now know is a
duplicated and condensed chromosome.
This condensed chromosome represents a highly compacted form of DNA and contains
tightly wrapped up chromatin. This chromatin itself is tightly packed up DNA and histone proteins. These different levels of compaction are what allow so much DNA to be packed into a
single nucleus. Therefore, going back to our question, letter X is what indicates chromatin.
