Mitosis Ana Djurica

Mitosis is cell division in the cell cycle, that ends with producing two identical cells-daughter cells. The 1st stage of cell division is interphase. Interphase is the phase of the cell cycle in which a typical cell spends most of it's life, the 'daily living' or metabolic phase of the cell, in which the cell obtains nutrients and metabolizes them, grows, reads it's DNA, and conducts other "normal" cell functions... It is divided into 3 phases; G1(gap phase 1), S(synthesis) and G2(gap phase 2). 

The ilustration of interphase

• G1-cell grows larger

• S-genome is replicated

• G2-separates the newly replicated genome and marks the end of interphase.

The cell cycle

Mitosis-events that occur in 4 phases of it:

1. Prophase-the spindle microtubules grow and extend from each pole to the equator, chromosomes super coil and become short and bulky and the nuclear envelope breaks down.
2. Metaphase-the chromatids move to the equator and the spindle microtubules from each pole attach to each centromere on opposite sides.
3. Anaphase-the spindle microtubules pull the sister chromatids apart splitting the centromeres. This splits the sister chromatids into chromosomes. Each identical chromosome is pulled to opposite poles.
4. Telophase-the spindle microtubules break down and the chromosomes uncoil and so are no longer individually visible. Also the nuclear membrane reforms. The cell then divides by cytokinesis to form two daughter cells with identical genetic nuclei.

Interphase+4 phases of mitosis

Sources:

•  http://ibguides.com/biology/notes/cell-division
• https://en.wikipedia.org/wiki/Interphase

MITOSIS

Mitosis is the  a process of cell division in which two new nuclei are formed, each containing the original number of chromosomes. The two newly formed nuclei are known as identical daughter cells. When mitosis occurs the chromosomes from one nucleus split into two matching sets which inhabit each daughter cell. The duplication and split of the chromosomes occurs in order for the twin daughter cells to be able to obtain information for future functions.

Figure 1:
The S stage

In order for this process to occur, each cell must undergo a repeating set of events, which occur in the beginning stages of the cell cycle also known as the interphase. The replication of genetically identical nuclei is reached through the four phases of mitosis; prophase, metaphase, anaphase and telophase. The first stage, the interphase can be further broken down into 3 stages/phases. The G1 stage, the S stage and the G2 stage. However the duplication of the DNA only occurs in the S stage. During the S phase, the DNA replicates resulting in the production of 2 copies of each chromosome, as shown in Figure 1. The cell then moves onto phase G2, where it continues to prepare for mitosis and cell division.

Mitosis, as mentioned above is a process composed of 4 stages, the first stage being prophase. During prophase the chromosomes, begin to condense or in other words thicken. The twin copies of each chromosome are called the sister chromatids. The nuclear membrane which surrounds and protects the cell nucleus disintegrates (breaks apart into pieces), the nucleolus then disappears, and the centrosomes move towards opposite poles of the cell. During the movement of the centrosomes the spindle fibers, which grow out of the centrioles, form and move to opposite poles of the cells as well. Metaphase is the second stage of mitosis. During this stage the duplicated chromosomes line up in the center of the cell. The spindle fibers are now fully grown and formed allowing them to attach itself to each sister chromatids. The third phase, anaphase occurs when the sister chromatids of each chromosome begin to divide. The centromeres which have moved to opposite poles of the cell, and hold the sister chromatids together, split resulting in the chromosomes moving away from each other along the attached spindle fibers. The last phase, telophase is the phase in which the two groups of chromosomes reach opposite ends of the cell. The nuclear membrane as well as the nucleus begin to form around each group while the spindle fibers detach themselves from the chromosomes.

Post the process of mitosis, the last and final stage of the cycle occurs. This stage is called the cytokinesis and it is the stage in which the cell along with the cytoplasm split and divide into two identical daughter cells. Each daughter cell is made up of its nucleus which is a replica of the genetic material from the ‘’parent cell’’.

Figure 2
Visual representation of the stages of mitosis 

Mitosis KKesic

How does mitosis produce two genetically identical nuclei?


Mitosis is a type of cell division that in the end produces two daughter cells, with each having the same kind and same number of chromosomes as the parent nucleus.
 Two daughter cells -  occurs when a cell undergoes the cell cycle. The cell cycle has a couple of phases.The first being the interphase; which, as well,  has a couple of stages. The first stage is when the cell grows and matures. The second is when the DNA is copied. The third is when the cell is prepared for division, at this phase the two daughter cells still are not format because their process starts in the mitosis phase but in that phase they are still not developed but the nucleus divides into 2 identical nuclei and from that point in the next phase the two daughter cells are formed.. Mitosis is where the devision of diploid eukaryotic nucleus. The development of the two daughter cells is completed in the cytokinesis phase where the division of the cytoplasm occurs to from two daughter cells.

Figure 1: Cell cycle - from mitosis to two daughter cells which each contain the exact copies of the parent cell's chromosomes.
(Google Images) 

Mitosis is divided intro four stages:

• Prophase - the spindle microtubules grow and extend from each other to the equator from each pole. As they become short an bulky the nuclear envelope breaks down.
• Metaphase - chromatids move to the equator and the spindle microtubules from each pole attach to each centromere on opposite sides.
• Anaphase - the spindle microtubules pull the sister chromatids apart ,which splits the centromeres. This splits the sister chromatids into identical chromosomes. As they are then pulled to opposite poles.
• Telophase - the spindle microtubules break down. The chromosomes unhelix and they are not individually visible. The nuclear membrane reforms. Then, the cell divides to from two daughter cells with identical genetic nuclei. 

During the prophase, the chromosomes become more visible under a light microscope as they superhelix and become shorter and more ponderous. Then, the nuclear envelope fractures. Afterwards, the spindle microtubules grow and extend from each pole to the equator. So, at the metaphase the chromatids move to the equator. The sister chromatids are are two DNA molecules, that are formed by DNA replication; that is also how they are identical. In the anaphase, these sister chromatids are separated. While the spindle microtubules attaches to centromere and pulls the chromatids to opposite poles. The chromosome then occurs - while the sister chromatids are separated they are called chromosomes. Which would mean that each pole has the same chromosomes ( it is the same genetic material). The final step is when the microtubules break down. While the chromosomes unhelix and the nuclear membrane reforms. Then the cell divides into two daughter cells with each having genetically identical nuclei.

Figure 2: How a chromosome looks when duplicated
(Google images)

In further detail, during the DNA replication each chromosome produces an identical of itself; but at this point they are called chromatids and they are attached at the centromere. Then, the chromatids separate at mitosis and from the two identical daughter nuclei.

Figure3: Two daughter cells - showing how they are exactly the same and have the identical nuclei.
(Google images)

Resources:

"IB Biology HL Exam Study." - LiveBinder. N.p., n.d. Web. 11 Nov. 2015.

"The Cell Cycle, Mitosis and Meiosis." — University of Leicester. N.p., n.d. Web. 11 Nov. 2015.

Allott, Andrew, and David Mindorff. IB Biology. Oxford: Oxford UP, 2014. Print. IB Diploma Program - Biology Course Companion.

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