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The Beginning of the Cell Cycle
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The first stage of the cell cycle is the same for all cells.
It is called Interphase. The cell will spend most of its
time in this stage and very little time in the second phase
known as Mitosis. (Actual division of cells).
At the beginning of this phase the cell grows slightly
bigger and begins to make more organelles. The most
important organelle that it makes is exact copies of the
chromosomes in the nucleus. Remember chromosomes
are the genetic material that determines what a cell is
going to be and do in the organism.
Now do not think that because we are humans and we
are smart creatures therefore we have a special number
of chromosomes. Humans have 46 chromosomes. A
potato has 48 chromosomes and a fruit fly has 8
chromosomes. A dog has 78 chromosomes. The most
shocking was that a Fern (type of tree) has 1,440
chromosomes. Wow!! Each type of organism has its
own specific number of chromosomes.
1. What is the first phase of the cell cycle? What happens in this phase?
2. Interphase used to be called the resting stage for a cell, but why is that an incorrect idea?
Mitosis
Once a cell has completed Interphase the cell will begin to divide. Because
everything in the cell has been copied, it is easy to slit into to new cells.
The process of mitosis is when the nucleus of a cell divides followed by
the cytoplasm. Once the cytoplasm spits into two the cell cycle is
complete and each cell goes back into Interphase.
The original cell, known as the parent cell will split into two exact copies
known as daughter cells. The daughter cells have exact copies of the
chromosomes and other organelles.
If something goes wrong in the cell cycle, like Interphase is not long
enough, it can cause things like cancer cell to form. Each new cell from
that original split will have the same problems and the cancer will form
what is known as a tumor.
Mitosis Four Phases
1. Prophase: This is the beginning phase of mitosis. The membrane that surrounds the nucleus disappears
so everything inside the nucleus is just floating in the cytoplasm. The chromosomes that usually look
like loose strings tighten up and pull together.
2. Metaphase: The chromosomes line up in the center of the cell. The chromosomes line up in a row, one
on top of the next. It almost looks like a dance is getting ready to happen in the center of the cell.
3. Anaphase: The copies of each chromosome separate moving to opposite sides of the cell resulting in
two sets of identical chromosomes. The separate like opposite ends of a magnet pushing as far apart as
possible.
4. Telophase: A nuclear membrane forms around the chromosomes in both cells. Each new nucleus
contains the exact same number and type of chromosomes as the original cell.
4. In what phase of mitosis are chromosomes moving toward opposite sides of the cell?
At the end of mitosis is a stage known as Cytokinesis. Simply put cytokinesis is when the
cytoplasm splits into two. This happens after mitosis and is the actual splitting of the cell.
See the animal cells to the left, the cells in the center are going through cytokinesis, the
splitting of the cytoplasm.