Mitosis comes after the interphase portion of the cell cycle (G1, S, and G2 phases), where growth and replication of cell structures and genetic material take place. The M phase includes both mitosis (where the replicated chromosomes separate into two sets) and cytokinesis (where the actual division takes place). In the G1 phase, chromosomes have only a single chromatid. During the S phase, the chromatid is duplicated, so the chromosome will have two sister chromatids. The spindle apparatus separates the chromosomes and consists of centrosomes, microtubules, and asters. Spindle fibers or microtubules are organized at the centrosome, a type of microtubule organizing center, and connect to the chromosome at the kinetochore. The phases of mitosis include prophase, metaphase, anaphase, and telophase, which each serve specific functions.
results in two identical daughter cells with the conservation of
mitosis, chromosomes are separated into two sets, one for each of
the two identical daughter cells .
spindle apparatus includes centrosomes, microtubules and asters.
Microtubules attach to the kinetochores on a chromosome.
is divided into four phases: prophase, metaphase, anaphase and
prophase, the nuclear membrane begins to break down and the nucleoli
disappear. The chromatin condenses and the spindle apparatus begins
metaphase, the chromosomes line up single file along the metaphase
anaphase, sister chromatids separate and are pulled to opposite
poles of the cell by the spindle fibers.
telophase, the nuclear membrane reforms and the chromosomes become
less condensed. The nucleoli also reappear.
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
Cytokinesis began during anaphase, and cytokinesis is the division of the cell into two physically separate cells by dividing the cytoplasm.1551
In animal cells, this occurs by the formation of a cleavage furrow. This is the cleavage furrow.1559
It is an indentation or a groove in this parent cell. Actin and myosin will pinch off this parent cell, so that it will pinch off and form two daughter cells.1564
When this is completed, when cytokinesis is completed, the end result is going to be two diploid daughter cells.1579
The parent cell was diploid. It had 1, 2, 3, 4 chromosomes.1590
This pinches off. We have still got four chromosomes.1594
Recall from a previous lecture discussing cytokinesis that formation of a cleavage furrow occurs in animal cells. It does not occur in plants and fungi.1598
Plants and fungi have cell walls. Instead of forming this cleavage furrow, they form, what is called, a cell plate.1611
The cell plate starts out as a coalescence of vesicles, and these vesicles are derived from the Golgi apparatus. They contain the materials needed to form a cell wall.1624
Cytokinesis in plants and fungi involves the formation of a cell plate via coalescence of vesicles derived from the Golgi apparatus.1644
And the materials in them are used to make a cell wall down the middle of the cell, and that will eventually divide the cell into two daughter cells.1654
Summing up mitosis starting out with two sets of two chromosomes. I had chromosome 1, chromosome 2, one maternally derived, the other paternally derived- maternally derived, paternally derived.1668
This cell is, therefore, 2n or diploid. It has been through S phase, so here are sister chromatids.1685
Each one of these chromosomes has enough information to supply two daughter cells.1694
Prophase, metaphase, anaphase and telophase occurred, and after that, the result is two daughter cells.1699
They are identical to each other. They carry all the information that the parent cell had, and they are diploid.1712
That is the most important points of mitosis. It is separation.1719
It is cell division resulting in two identical daughter cells with conservation of chromosome number.1724
Alright, to practice, we are going to look at four examples.1732
Label the parts of the spindle apparatus below. What is the name of the structure on the centromere to which the spindle fiber is attached?1736
Starting out with this first part, here, I have a centrosome. Within it, what is really shown here is the centriole, but the centrioles are a part of the centrosomes.1745
Remember that the centrosome is a microtubule-organizing center, and within each one is two centrioles- same thing on the other side.1758
Radiating out in a star pattern is an aster, so there is an aster on this side and an aster on the other side.1768
Here, I have spindle fibers or spindle microtubules. These are composed of microtubules, hence, the name, and these are attaching to the sister chromatids.1778
This next part of the question asks me what is the name of the structure to which the spindle fiber is attached.1792
The centrosome is here in the middle holding the sister chromatids together, and on the centrosome are two kinetochores.1798
The spindle fibers from one pole attach to one kinetochore. The spindle fibers on the other pole attach to the other kinetochore giving the setup that will allow the sister chromatids to be pulled apart.1811
The answer to this question is that the spindle fiber is attached to the kinetochores, and the kinetochores are located on the centromere.1825
Second example, example two: What is the last phase of mitosis called? What occurs during this phase?1839
The last phase of mitosis is telophase. Remember, there is PMAT: prophase, metaphase, anaphase, telophase.1850
Some of the events here are actually just a reverse of prophase.1862
Remember in prophase, the nuclear membrane broke down. Now, the nuclear membrane reforms, and one nuclear membrane will form around one set of chromosomes at one pole of the cell.1869
The other nuclear membrane will form around the other nucleus at the other pole of the cell, so now, there are two nuclei.1887
The second event: recall that chromatin condensed in prophase. Now, chromatin becomes less condensed.1896
Once is decondenses, the chromosomes are not going to be visible via light microscopy.1915
During prophase, the spindle apparatus formed. Now, spindle apparatus breaks down.1921
In addition, the nucleoli reappear. Also, you should note that cytokinesis is continuing on.1936
It began in late anaphase. It is also continuing on during telophase, but it is often treated as a separate phase.1946
So, for telophase, we are going to put these four events as telophase and keep cytokinesis considered as a separate event.1953
Example three: list three events that occur during prophase of mitosis.1962
Remember, we just talked about telophase. That makes this question easy.1974
It is the opposite. Here, we are going to have breakdown of the nuclear membrane.1977
The next event is going to be that the chromatin condenses. It becomes wound more tightly.1990
Now, the chromosomes are going to be visible via light microscopy.1998
The spindle apparatus begins to form in preparation for anaphase when sister chromatids are going to be separated, so the spindle apparatus begins to form.2004
During this phase, the nucleoli disappear. They are no longer visible.2017
OK, prophase is the first phase of mitosis, and these four events occur during prophase.2024
Example four: What phase is the cell below shown in? What events occur during this phase?2036
Looking at this situation here, I see that the sister chromatids are being pulled apart. Since they are being pulled apart, I know that this cell is in anaphase.2045
The main event of anaphase is separation of sister chromatids.2061
This cell started out with four chromosomes, with sister chromatids. Now, the spindle fibers are going to shorten.2075
They are going to pull just towards each chromatid, towards the opposite pole of the cell resulting in daughter cells that have 1, 2, 3, 4 chromosomes but only one sister chromatid.2082
That concludes this lesson on mitosis here at Educator.com.2096
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