Download THE CELL CYCLE

Ch4 Sec3 Notes
THE CELL CYCLE
NAME ____KEY________________
DATE ____________ BLOCK _____
1. Life Cycle of Cells (Cell Cycle)
a. The cell cycle begins when the cell is formed and ends when the cell
_divides_______ and forms ___new cells___________.
b. Before a cell divides, it must make a copy of its _DNA____ or chromosomes.
2. Cell division in prokaryotic cells is simple. The bacteria make a duplicate copy of
their circular DNA and then divide into two cells, each receiving a copy of DNA and
some ribosomes. This process is called _binary fission____________________.
3. Eukaryotic cells have much more DNA than prokaryotic cells. The DNA and proteins
make up the chromosomes inside the nucleus
a. The number of chromosomes varies from one type of organism to the next.
Humans have _46__ chromosomes in each cell in their body.
b. The 46 chromosomes are actually 23 pairs of matching chromosomes
(one set from the mother and one set from the father.)
c. Matching pairs of chromosomes are called __homologous_
__chromosomes_______. Humans have 23 pair.
4. The cell cycle of eukaryotic cells begins when a cell is formed. It will grow and
carry on life processes. At some point it will get ready to divide into two cells.
a. In the first stage, the cell will make duplicate copies of its
___organelles____________ and __chromosomes_________.
b. Each chromosome is attached to its duplicate and is called a __sister
chromatid_. The structure holding the two identical chromosomes together is
called a ___centromere_______. Label both below.
centromere
Sister chromatid
c. In the second stage, the chromatids will separate. This process is called
___mitosis___________.
d. The purpose of mitosis is to separate the chromatids so that each new cell
will receive the correct number of chromosomes.
e. To pull the chromatids apart, the centriole forms spindle fibers that attach
to the centromere. The spindle fibers pull the chromatids to opposite sides
of the cell.
f. The third stage of the cell cycle occurs once the chromatids reach the
opposite sides of the cell. The cell is now ready to go through
__cytokinesis__________, which is division of the cell.
g. The result is two cells identical to the original cell.
5. We are going to follow the cell of an organism that is dividing and making two new cells.
This organism has 6 chromosomes or 3 homologous pairs in every cell.
Draw them in the cell below:
One chromosome from each homologous pair
comes from the mother and one
comes from the father.
At the end of Interphase, in preparation for cell division, changes occur in the
chromosomes. Draw them below:
Chromosomes are copied. Each chromosome
consists of 2 chromatids connected by a
centromere.
Centrioles are copied.
The first phase of mitosis is called Prophase. Draw it below:
Nuclear membrane breaks apart.
Chromosomes become rod like.
2 centrioles move to opposite sides of cell.
Fibers form between centrioles and
attach to centromeres.
The second phase of mitosis is called Metaphase. Draw it below:
Chromosomes are pulled by the spindle fibers
to line up randomly along equator of cell.
The third phase of mitosis is called Anaphase. Draw it below:
Chromatids separate and are pulled to opposite
sides of cell by spindle fibers.
The fourth and last phase of mitosis is called Telophase. Draw it below:
Nuclear membrane forms around two sets of
chromosomes.
Chromosomes unwind = chromatin.
Mitosis is complete.
Cytokinesis completes cell division. Draw it below:
Cytoplasm splits in two.
In animal cell, cell membrane
pinches inward.
In plant cell, cell plate forms in
middle of cell.
The result is two cells that are exactly
like the original cell.