Video Transcript
Which is the correct sequence of
events that occur when a somatic cell divides? (A) Chromosomes become visible,
chromosomes duplicate, cytoplasm divides in two, and duplicated chromosomes
separate. (B) Chromosomes duplicate,
duplicated chromosomes separate, chromosomes become visible, and cytoplasm divides
in two. (C) Chromosomes duplicate,
chromosomes become visible, duplicated chromosomes separate, and cytoplasm divides
in two. (D) Chromosomes become visible,
chromosomes duplicate, duplicated chromosomes separate, and cytoplasm divides in
two. (E) Chromosomes duplicate,
chromosomes become visible, cytoplasm divides in two, and duplicated chromosomes
separate.
Let’s start with some key
terms. We’re asked about a somatic cell
dividing. We might remember that a somatic
cell refers to any general type of body cell other than our reproductive cells, such
as sperm and egg, and that somatic cell division is mitosis. So, in this question, we’re
essentially being asked about the sequence of events in mitosis. So let’s quickly review those
events now.
We should first remember that
before any type of cell division, all of the cell’s DNA will duplicate during
interphase. And then during mitosis, there are
four stages that occur: prophase, metaphase, anaphase, and telophase. So let’s quickly review more
closely what happens during each of these four stages of mitosis.
During prophase, the loose strands
of DNA, or chromatin, that were present in the nucleus during interphase coil up
into highly condensed and visible chromosomes. Also, the nuclear envelope or the
membrane around the nucleus dissolves so that the chromosomes can be moved more
easily around the cell. These centrosomes, which produce
the mitotic spindle, start to produce their fibers and migrate to opposite ends of
the cell.
In metaphase, the mitotic spindle
fibers attach to the centrosomes of the chromosomes and move them into a single-file
row along the equator or midline of the cell. Then, in anaphase, the sister
chromatids or duplicated sides of each chromosome separate and are pulled by the
mitotic spindle fibers towards opposite ends of the cell. Then, in telophase, the cell
membrane starts pinching in, and the one original cell begins to actually physically
divide into two separate daughter cells. Meanwhile, the nuclear envelope or
the membrane around the nucleus begins to reform at each end of the dividing
cell. And the highly coiled and highly
condensed visible chromosomes inside each of those nuclei begin to decoil and
decondense back into loose strands of DNA or chromatin.
So we could summarize this process
by saying first the DNA inside of the cell duplicates during interphase. Then, during prophase, the
chromosomes condense and become visible. During metaphase, the chromosomes
line up along the midline or equator of the cell. And during anaphase, the sister
chromatids or two replicated sides of the chromosomes separate and are pulled to
opposite ends of the cell. Then, during telophase, the cell
membrane and all of the contents inside of the membrane, known as the cytoplasm,
begin to physically divide into two separate daughter cells.
So let’s look at our answer choices
and determine which shows the correct sequence of events that occur when a somatic
cell divides. We know that the first thing that
happens during interphase is that all of the DNA or chromosomes in the cell
duplicate. So we can eliminate (A) and (D),
since the first event in these sequences is not that the chromosomes duplicate. We also know that one of the first
things that happens during the process of mitosis is that the chromosomes coil up
into a highly condensed state and become visible. So we can eliminate (B), which has
the duplicated chromosomes separating before the chromosomes become visible. After the chromosomes become
visible, we know that they line up and separate. So we can eliminate (E), which has
the cytoplasm dividing in two before the duplicated chromosomes separate.
So our correct answer is (C). The correct sequence of events that
occurs when a somatic cell divides is that the chromosomes duplicate, chromosomes
become visible, duplicated chromosomes separate, and the cytoplasm divides in
two.
