Welcome back to BOGObiology. This is five
minute bio, where we discuss a key
scientific concept in five minutes or
less.
Today's topic is the cell cycle. Today
we're going to ask ourselves the
questions "What is the cell cycle?"
"What is its purpose?" "What happens in each
phase?" and also "What happens when it goes
wrong?". The cell cycle is a sequence of
events in the life of the cell beginning
with its creation from another cell and
ending when it divides. The cell cycle
occurs in order to replace old cells, and
also to allow for the growth and
development of the organism. Eukaryotic
cells have two major phases; interphase
and mitosis. In interphase, the cell grows
and it also duplicates its genetic
material. In mitosis, it divides and forms
two new cells called daughter cells.
Before we go any further, notice that the
cell spends the vast majority of its
lifespan in interphase, not in mitosis.
Also notice that both interphase and
mitosis are split up into multiple
sections. To help us keep the different
phases organized, I created this chart
and you may want to do the same.
Before we get started, see if you can
figure out what each of these colorful
boxes corresponds to. And, for now, ignore
this one right here, we're going to come
back to it. Hopefully you labeled your
chart something like this. We're going to
start with the G1 phase. During the G1 or
"Gap 1" portion of interphase, the cell
grows and it also creates mRNA and
protein before moving on to the S Phase.
However, the cell will undergo something
called the G1/S checkpoint. The cell
checks to make sure that all of the
procedures have been completed correctly.
If they have, the cell will move on to the
S Phase. If the cell detects insufficient growth
or errors in its genetic material, it will
likely enter in what's called the G0
phase instead. A damaged cell would
therefore no longer be able to continue
dividing. Certain types of cells will
also purposely enter the G0 phase.
Two examples are neurons and muscle
cells, which don't continuously divide
the way that most cells do. Once they have
grown to their full size, they will live
out the rest of their lives in G0. Most
cells will proceed to the S Phase, where
they will continue to grow and then also
will copy over their DNA. The "synthesis"
that occurs during the S Phase is actually
where this phase gets its title from. The
last of the three parts of Interphase is
called G2. Here, the cell will continue
to grow and will also create a few
organelles that it needs in order to
divide. Before proceeding to mitosis and
actually dividing, the cell goes through
yet another checkpoint. The DNA is
scanned for damage one final time. The
cell will attempt to repair any damaged
areas of DNA before proceeding on to
mitosis. We have now entered the M
Phase of the cell cycle. In prophase, the
genetic material begins to condense.
During metaphase, the chromosomes of
genetic material line on the metaphase
plate. Spindle fibers attach to each one and
prepare to pull the genetic material to
opposite poles. It is absolutely essential
that the spindle fibers correctly
attach to each pair of chromatids. Once
in anaphase, the sister chromatids begin
to be pulled towards opposite sets of
poles. In telophase, cytokinesis occurs.
The cell
splits into two new cells and the process can
begin all over again.
We now need to ask ourselves the
unpleasant question of "what happens when
this goes wrong?".
Usually the series of checkpoints is
excellent at preventing mistakes from
happening during cell division, but
occasionally mistakes are still made.
We're going to look at two types of
common errors, and both of them have to
do with a malfunction of one of the
checkpoints. If an error occurs of the G1
checkpoint, it often results in increased
cell division.
When damaged unhealthy cells divide far
too rapidly,
we call it cancer. If an error occurs at
the M checkpoint rather than the G1
checkpoint, it results in aneuploidy.
Let's imagine that the attachment of the
spindle fibers during this step here
didn't go correctly and thus we wound up
with too many chromosomes on the
right-hand side of the cell during
anaphase. This would lead to both
daughter cells having an incorrect
number of chromosomes. This is what
causes trisomy 21 also known as Down
Syndrome.
OK, that's it for today. If you found this
video useful, I hope you'll let me know
by hitting the "like" button, or leaving me
a comment down below. As always, please
remember to cite your sources.
I've listed the ones that I used to make
this video below and you can also find a
ready-made APA citation for this video
in the video description. Thanks for
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