Video Transcript
In which stage of cell division do
the chromatids separate and move toward the poles?
To answer this question, let’s
first review the cell cycle and then look at the different steps during cell
division, or mitosis.
In order for an organism to
develop, cells need to divide. This is so the organism can grow
and can replace damaged tissue. Cell division takes place during
the cell cycle. The cell cycle can be broken up
into interphase and mitosis. Actual cell division takes place at
the end of mitosis. In order for the cell to divide, it
needs to make a copy of itself, including all of its DNA. This happens during a stage called
interphase. Before DNA is copied, it exists as
long chromosomes that are all mixed up together. In humans, we have 23 pairs, or 46
chromosomes in total. For simplicity, let’s just pretend
there’s two chromosomes so we can see what’s happening more easily.
During interphase, these two
chromosomes duplicate to make a copy of themselves. Each duplicated copy is now called
a chromatid, and each chromosome is now made up of two sister chromatids. Now that the DNA is copied, this
marks the end of interphase. Now, mitosis can begin, which is
broken up into four different steps called prophase, metaphase, anaphase, and
telophase.
During prophase, the duplicated
chromosomes from interphase begin to wrap up tightly and condense to form a
duplicated and condensed chromosome structure. This X-shaped chromosome shape is
what you’re probably used to seeing represented as a chromosome. Only during prophase are we finally
able to make out the individual chromosomes. Additionally, during prophase, the
mitotic spindle fibers begin to form from the centrosomes and the nuclear membrane
begins to break down.
In the next step, called metaphase,
the centrosomes are at the poles of the cells with the duplicated chromosomes along
the equator of the cell. The spindle fibers attach to each
of the sister chromatids in the duplicated chromosome.
In anaphase, these two chromatids
are separated by the retracting spindle fibers so each chromatid goes to each pole
of the cell.
During telophase, the two
chromatids, which we can now call chromosomes, arrive at the poles of the cell as
the cell begins to divide in two. A new nuclear membrane forms around
the chromosomes, and the chromosomes begin to decondense and are no longer visible
under the microscope. The two copies of the cell are
identical to one another.
Now that we’ve reviewed the cell
cycle, let’s go back to our question and see if we can answer it. The stage of cell division when the
chromatids separate and move toward the poles is known as anaphase.
