Download Cytokinesis - Catawba County Schools

Cell Division
Mitosis
Vocabulary
Chromosomes
are thread-like structures located inside the nucleus of animal and plant cells.
Each chromosome is made of protein and a single molecule of
deoxyribonucleic acid (DNA)
DNA
Deoxyribonucleic acid, a self-replicating material present in nearly all living
organisms as the main component of chromosomes. It is the carrier of genetic
information.
Chromatids
are two identical copies of a single chromosome that are connected by a
centromere. They occur as a result of a chromosome that duplicates during
the prophase stage of the cell division
Copy the following questions your science notebooks and provide a complete answer for
each
What is cell division?
What is the difference between meiosis and mitosis?
What phase is not included in mitosis?
Which phase of cell division last the longest? Why?
How many chromosomes are in a normal human cell? How does this change during mitosis?
What are centrioles and what role do they play in mitosis?
In what phase does the membrane of the nucleus begin to break down?
What are spindle fibers and what role do they play in mitosis?
How is the cytokinesis phase different from the other phases of mitosis?
What happens that causes cancer cells to grow and how does this effect the
organism?
Cell Division
Cell division is the process that cells go through in order to divide. Cells may
divide for several reasons, and there are two types of cell division depending
on the purpose. The cell division associated with sexual reproduction is one
type, called meiosis. The other type, the cell division associated with growth
and cell replacement or repair, is called mitosis. In both types of cell division,
the nucleus splits and DNA is replicated.
The cell division called mitosis produces daughter cells that have all the
genetic material of the parent cell — a complete set of chromosomes.
However, chromosomes are not the only material that needs to be
divided and transferred to the daughter cells: there are cytoplasm and the
cell membrane to divide as well.
Cytokinesis is the process of dividing the cytoplasm and the cell
membrane, and this process may follow immediately after mitosis or
occur separately, depending on the organism involved. Together, these
two processes make up the mitotic phases of the cell cycle.
Cell division consist of a series of steps or phases.
These phases are Interphase, prophase,
metaphase, anaphase, telophase, and
cytokinesis
Interphase, which is the foundation building stage
during, the parent cell, or original cell makes a copy
of its genetic material so that each daughter cell can
have a complete set. Therefore, mitosis is an
ongoing and repetitive process, that begins with
interphase over and over again..
Instructions:
As you go through this lesson, identify in your science notebook each phase of
mitosis and explain what is occurring in each phase. Along with your explanation
of each phase, make and label an illustration of each phase.
You will be expected to identify organelles within the cell, state what mitosis
phase a cell is in by observing an image and / or by a given explanation of what is
occurring in the cell.
Begin by continuing to the next slide.
This lesson will illustrates mitosis—the division of a cell's nucleus.
Along with cytokinesis (the division of the rest of a cell), mitosis results
in a parent cell dividing into two daughter cells. The genetic
information within each of these daughter cells is identical.
A human cell contains 46 chromosomes. However, to simplify your
illustration, you will only see four..
Interphase
Centrioles are short cylinders
with a 9+0 microtubule
triplet that helps in
organizing spindle fibers
and direct organization of
microtubles
Interphase is the period between cell divisions. It is the longest phase. During this
time, chromosomes replicate—each DNA strand unzips into two strands while freefloating bases attach to the unzipped strands. The chromosomes are loosely
packed and not visible with a microscope.
Two pair of centrioles lie just outside the nucleus, next to each other. A centriole is
a cylinder type structure within the cell that plays a part in cell reproduction.
Prophase
Chromatid
Chromosomes begin to condense, taking on the form that they are usually depicted in:
four arms connected at a point. Each chromosome is, at this time, actually two identical
copies. Each copy is called a chromatid.
A spindle begins to form from the centrioles. This spindle is made of fibers. The
centrioles begin to separate and the membrane of the nucleus, or nuclear envelope,
fragments and disperses.
Metaphase
Sometimes referred to
as Prometaphase
Spindle fibers are protein
structures that pull apart the
genetic material in a cell
when the cell divides.
The centrioles are now at opposite ends of the cell. The spindle fibers from
both of the centrioles attach to each one of the chromosomes.
Metaphase
The chromosomes line up on the metaphase plate, an imaginary line that divides
the cell in two. The spindle fibers begin to tug each chromosome toward opposite
ends of the cell.
Anaphase
The spindle fibers pull the chromatids toward opposite ends of the cell.
Telophase
The chromatids (now also considered chromosomes) arrive at the opposite ends
of the cell, and new nuclear membranes form.
Mitosis, which describes only the division of the nucleus, is now complete.
Cytokinesis
In cytokinesis the rest of the cell divides and the division of the cell's cytoplasm,
is now complete. The entire process of has been complete with a result of two
identical cells.
Now, review the entire mitosis process again by clicking the link
below. In addition pay particular attention about the discussion of
cancer cell.
Video Clip: Mitosis and Cancer Cells
Cell Division
Meiosis
Meiosis
Copy the following questions your science notebooks and provide a complete answer for
each
How many chromosomes does a egg cell and sperm cell have?
What does the term Cross-over refer to?
In meiosis, what phase does the chromosomes share genetic information
How is Interphase II different from Interphase in mitosis and
Interphase I in meiosis?
In meiosis, how is prophase I and prophase II different?
List all the phases of meiosis in the correct order.
Meiosis
Before We Split
Though the genetic code of a human being is contained within 46 chromosomes, only half of
this number exists within the cell of a sperm or egg. If the cells didn't have half, a fertilized egg
would contain 92 chromosomes and be untenable. Meiosis, a type of cell division specific to
reproduction, avoids this by halving the number of chromosomes in a cell.
The cell shown here will divide twice, resulting in four cells. Each of these cells will have only
half the number of chromosomes, but each chromosome will contain genetic information from
both parents.
Interphase I
The activities within this cell are the same as in the mitosis-dividing cell.
NOTE: Blue indicates chromosomes from the father; orange indicates chromosomes
from the mother. The titles used for each step—e.g., "Interphase," Interphase I"—are
those used in biology textbooks.
Prophase I
Notice that the fathers
chromosomes are paring up with
a pair of chromosomes from the
mother. It is at this point where
genetic information is shared
between mother and father and
the pairing creates a new
chromosome pattern which
results in the creation of a new
unique individual. This type of
Orange indicates
pairing and sharing of genetic
mothers chromosomes
material is referred to as
Crossing-over
Blue indicates father
chromosomes
The activities are the same as in mitosis, except that in this cell the chromosomes attach to
the membrane of the nucleus and then pair up with their corresponding chromosome.
While paired up, enzymes cut sequences of DNA (genes) from the chromosomes. These
sequences are exchanged between the chromosomes, which allows for an exchange of
genes between the two
Metaphase I
Same as in mitosis, except that the spindle fibers from each centriole attach to one
chromosome of a matching chromosome pair.
In other words, the fibers from one centriole attach to 23 chromosomes, and the fibers from
the other centriole attach to the other 23 chromosomes. (Again, only four chromosomes are
shown here in order to simplify the illustration.)
Metaphase I
Father’s chromosomes
Mother’s chromosomes
Father’s chromosomes
Mother’s chromosomes
Same as in mitosis, except that the chromosome pairs line up on either side of the
metaphase plate.
Anaphase I
Now as you view each chromatid, you
can see a trace of the other parent
genetic material on the new
chromosome. This process reoccurs
each time a cell divides which leads to
enormous variety with the genetic
code.
Mother & Father
Mother & Father
The chromosome pairs separate; half of the chromosomes move toward one end of the cell,
the other half, to the other end. The chromosomes' sister chromatids do not separate as they
do in mitosis.
Telophase I
As in mitosis, the chromosomes arrive at opposite ends of the cell, and new nuclear
membranes form.
The dividing cell shown here is a male's sperm cell. With meiosis in a female, most of the cell's
cytoplasm will be concentrated in one of the two emerging cells, which will result in one large
cell and one small cell.
Cytokinesis
Identical to mitosis.
This concludes the first part of Meiosis.
View the video clip and complete your information
with what is being said in the video. They should be
similar.
Video Clip: Part 1 on Meiosis
Interphase II
The chromosomes do not replicate during this phase, as they do in
interphase in mitosis and interphase I in meiosis
Prophase II
In this phase the DNA does not
get copied. The chromosomes
do not pair up and do not
exchange information as they
did in prophase I
As in prophase I, the chromosomes condense, spindles form, the centrioles begin to
separate, and the nuclear membrane fragments and disperses.
Unlike prophase I, the chromosomes do not attach to the nuclear membrane in order to
exchange genetic information.
Metaphase II
The spindle fibers attach to the chromosomes. The centrioles are now at opposite ends of the
cell. As in mitosis in this part of metaphase, fibers from both ends of the cells attach to each
one of the four chromosomes.
Metaphase II
The chromosomes align along the metaphase plate. As in mitosis metaphase, (and unlike
meiosis metaphase I), fibers from the centrioles begin to pull on each one of the
chromosomes from both directions.
Anaphase II
As in anaphase in mitosis (and unlike anaphase I in meiosis), the fibers pull the
chromatids apart and toward opposite ends of the cells.
Telophase II
The chromatids arrive at the either end of each cell and new nuclear membranes form.
Cytokinesis
End of cytokinesis
The rest of the cell continues to divide. Only when two, distinct cells form will
cytokinesis, the division of the cell's cytoplasm, be complete.
There are now four daughter cells. Each cell has one set of chromosomes, or one half
the number of the initial cell.
This completes the 2nd part of meiosis. As you did with the
first part, compare your data with information from the video
clip. They should be similar.
Video Clip: Meiosis: Part two