Video Transcript
What structure, shown in the figure, is present inside a nucleus?
This question is asking us about an X-shaped structure found within the nucleus of
cells. The nucleus is one of the most important organelles in the cell because it contains
all of the instructions to give us all of our characteristics. These instructions are contained in our DNA. In humans, our DNA is organized into 46 structures called chromosomes. It’s hard to see the individual chromosomes here because they’re all mixed up. So let’s remove all but two chromosomes so we can see this better.
When our cells aren’t dividing, our DNA exists as long molecules of DNA that aren’t
very compacted. This is called chromatin. When it’s time for the cell to divide and start mitosis, this DNA needs to be
copied. So, here, in the diagram, we can see these two chromosomes have duplicated. Because these are very long molecules of DNA, it would be hard to separate them
accurately into new cells.
So, next, the chromatin needs to condense or become compacted so the chromosomes are
smaller and easier to work with. Here’s what the chromosomes look like when they’re condensed and duplicated. It’s at this stage that we can see them under a microscope. As mitosis continues, the condensed and duplicated chromosomes line up along the
equator of the cell. And the spindle fibers begin pulling the duplicated chromosomes apart, while the cell
begins to divide. After mitosis, there’s two cells, and the condensed chromosomes can uncondense, and
they look like they did before mitosis began.
To get back to our question, the X-shaped figure we see in the nucleus in the
provided diagram is a chromosome.
