BioWiki Project Topic - MITOSIS

A-Team BioWiki - Mitosis

Wiki Contents:

• Introduction to Mitosis
• Stages
• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase

• All Phases of Mitosis (Video)
• Errors in Mitosis
• Apoptosis: A Cell's Suicide (Video)
• Mitosis Vs. Meiosis
• Brief Description of Meiosis
• Outcomes of Errors in Meiosis
• Scientific Articles 
• References    

Introduction to Mitosis:

• Mitosis is a process of cell division which results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell.(1)

Stages Before Mitosis:

• Before Mitosis occurs, the cell goes through interphase, which is not necessarily part of the mitosis cycle.  Interphase consists of a G1 phase, S phase, and finally the G2 phase to initially start the process of mitosis. (1)
• During the G1 phase, the chromosomes are single structures.  During the G1 phase, the cell will pass a "Restriction point" where the cell transitions from the G1 phase to the S phase.  This point is where the cell has committed to create DNA replication and eventually cell division.(1)
• During the S phase, the DNA is completely replicated and one chromosome becomes two sister chromatids.  At the end of this phase, the cell will enter the G2 phase where the cell initially starts the mitosis process.(1)
• During the last phase, G2, the cell prepares for mitosis. (1)
• From here mitosis begins with Prophase, then Prometaphase, Metaphase, Anaphase, and lastly Telophase.(1)

Stages:

Prophase:

• This is the beginning stage of mitosis.  Chromatin is condensed into a structure called a chromosome.  This is when chromatids become visible.  Kinetochores develop within the centromere regions which then allow the chromatids to migrate to the cell centrosome.  The mitotic spindle consisting of microtubules and other proteins, form between the two pairs of centrioles as they migrate to opposite poles of the cell in the cytoplasm. The nuclear envelope breaks down while the strands of chromatin form into chromosomes.    (1)

url: http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/prophase.gif

Prometaphase:

• During prometaphase the nuclear envelope breaks down and disappears.  Kinetochore microtubules coming from the centrosomes attach to the chromosomes’ kinetochores.  When the microtubules attach to the chromosomes prometaphase is complete. (1)

url: http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/prometaphase.gif

Metaphase:

• The chromosomes align at the equatorial plate and are held in place by microtubules attached to the mitotic spindle and to part of the centromere. In mitosis, during the stage of metaphase, individual chromosomes align in the center.  The chromosomes, at this point, consist of two chromatids. This stage follows prometaphase and precedes anaphase.(1)

                                       url: http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/metaphase.gif

Anaphase:

• Anaphase is the stage of mitosis when chromosomes separate in a eukaryotic cell. Each chromatid moves to opposite poles of the cell, the opposite ends of the mitotic spindle, near the microtubule organizing centers. During this stage, anaphase lag could happen. Anaphase begins when the duplicated centromeres of each pair of sister chromatids separate, and the now-daughter chromosomes begin moving toward opposite poles of the cell due to the action of the spindle. Depending where the centromere is located along the chromosome, a characteristic shape appears during chromosome movement. The two shown above give V and J shapes. At the end of anaphase, a complete set of chromosomes has assembled at each pole of the cell.(1)

url: http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/anaphase.gif

 Telophase:

• Telophase is the final step of the Meiosis and in comparison is the inverse of prophase.  As Telophase begins, the nuclei continue to lengthen and making the cell stretch even more.  The chromosomes start to assemble in sets as the sister chromosomes start to attach at the opposite ends of the cell. Then, the chromosomes begin to uncoil and become less condensed in the cell. As the cell is shaping, two nuclear envelopes start to form around each of the unreplicated chromosome set, the spindle disappears, and the nucleolus reforms. At this point the nucleus division completes. A stage that most commonly is mistaken for the last stage of Mitosis is Cytokinesis which is seperate from telophase and not a process of Mitosis. (1)

                                                url: http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/telophase.gif

All Phases of Mitosis (Video):

Errors in Mitosis:

• If something were to go wrong in mitosis it tends to lead to genetic disorders and diseases. (4)
• Anaphase lag is mechanism where one chromosome simply fails to get incorporated into the nucleus of a daughter cell. Anaphase lag describes the delayed movement during anaphase of one homologous chromosome in meiosis or of one chromatid in mitosis. The result is that the lagging chromosome is not incorporated into the nucleus of one of the daughter cells and there will be one normal cell and one cell with monosomy. In this event, the lagging chromosome is lost. The analysis of chromosomes during this stage is key to cancer.   (4) 
  
• The possible malfunction in telophase can include an improper separation at the end poles. Non-formal size of the chromatids.  If Telophase happens too early, splitting before the copy is made can create an dysfunctional cell and chromosomes.  (4)
• Malfunctions in mitosis gives a signal to conduct cell death, apoptosis. we learned in class that apoptosis is signaled when a cell becomes un-needed or if the DNA is damaged. if errors occur in mitosis mostly likely it will damage the DNA triggering Apoptosis. If such an event does not occur cancer cells will form and start growing, mobilizing, and the person will eventually die from cancer.  Apoptosis is when cells have regulated cell deaths and is usually signaled by un-needed cells or cells with damaged DNA. These kind of cells usually trigger apoptosis, but for those that don’t become a form of cancer cells.  If these cells do become cancer cells they continue to grow non-stop and metastasis, or spread throughout the body. Treatments of cancer target the cell cycle. In class, we learned about some drugs that treat cancer in certain ways such as 5-flourouracil block thymine, a base in DNA and another drug for example, Taxol, interferes with mitotic spindle.   (4)

A Cells Death By Apoptosis (Video):

Mitosis vs. Meiosis:

• Mitosis and Meiosis are commonly misused for the wrong cell division. Mitosis is mainly used for cell division for somatic (body) cells while meiosis is for sexual reproduction cells. Mitosis only goes for one round cell division ending with two identical daughter cells while meiosis goes through two divisions. One of the differences between mitosis and meiosis is that meiosis looks to reduce the chromosome number from diploid to haploid. People often confuse it by stating that without mitosis you wouldn’t have children, but its actually without meiosis that one cannot have children. Also, meiosis has more phases to go through even after cytokinesis. (3)  

Mitosis Vs. Meiosis

url:http://www.bestlibrary.org/sc9/files/mitosis_vs_meiosis.jpg

Brief Description of Meiosis:

• Meiosis is the production of sexual cells by a double division.  Meiosis consists of two different division parts (Meiosis I & Meiosis II) which both contain prophase, metaphase, anaphase, and telophase.  Meiosis is very important for the genetic diversity of sexual reproduction.  (2)
• During Meiosis the number of chromosomes a diploid has is reduced to a haploid. (2)

Stages of Meiosis:
--Before Meiosis even begins, the phases of G1 & G1 occur where the cell signals for chromosomal separation and DNA replication. G2 phase is absent in the Meiosis process.  (2)

• Prophase I- During this phase, DNA is exchanged between homologous chromosomes by crossovers of chromosomes which creates genetic diversity. This may result in a combination of alleles from each parent.  The new chromosomes are now called tetrads which consist of two chromosomes (one from each parent) and 4 chromatids. Non-sister chromatids may crossover in this stage called chiasmata.  (2)
• Metaphase I-During this phase, chromosomes line up at the equatorial plate while the homologous pairs are held by the chiasmata. (2)
• Anaphase I- During this phase, the homologous chromosomes separate and daughter nuclei contain only one set of chromosomes, each with two chromatids. (2)
• Telophase I- During this phase, nuclear envelope reappears.  Yet, this only occurs in some organisms.
• After Telophase I, interphase occurs called interkinesis which begins the 2nd part of Meiosis.  (2)
• Prophase II, Metaphase II, Anaphase II, and Telophase II occur again creating a 2nd set of genetically different sexual cells, completing the cycle with 4 new daughter cells. (2)

                      url: http://media-2.web.britannica.com/eb-media/88/78588-036-DAFF2140.jpg

Outcomes of Errors in Meiosis:

• It is said to be that 10-25% of all chromosomal eggs contain abnormalities.  Sometimes these are common in pregnancy failure.(4)
• These chromosomal abnormalities usually arise in Meiosis I. This becomes more frequent as a woman ages. (4)
• The most common abnormality is called aneuploidy; this is the gain or lose of one whole chromosome.  This usually occurs when a nondisjunction occurs, resulting in monosomy and trisomy.  This means the chromosome failed to separate. (4)
• An incorrect amount of chromosomes could produce a disease such as down syndrome or could cause the sex cell to be damaged and unable to develop for birth. (4)

url: http://schoolworkhelper.net/wp-content/uploads/2010/11/nondisjunction.jpg

Review of Two Scientific Articles:

Article #1: New Findings on Chromosomes change in tumor cells

• A recent article published by Science Daily focused on cell growth. The article was discussing of a recent experiment done at a European college showed new findings on tumor cells. We have known prior that cancer cells divide in different ways as opposed to normal cell. We have believed that from research before many changes in chromosomes occur over long periods of time. In the study done at these European universities, they watched a film of tumor cells for an extended period and found reasonable evidence to show that it does not take long periods of time for tumors cells to have many changes. It only takes little time for many different adaptions to take place.  This articles does have many evidence and references to back to its story and does go into to detail about the new findings. The researches who found this new information of tumor cells ensured that proper research was done by linking the article to the actual write up from the actual experiment. The article does state that it is not meant to be used for actual application yet,  but that it is still  in the early stages of helping to get more knowledge of tumor cells. The experiment was done in  a fashion of precision when recording division of tumor to describing what is actually happening.  This article is relevant to the topic of this page because error in cell division probably caused the tumor to form and due to the uncontrolled cell division it is probably growing at an uncontrollable rate.(6)

Article #2: Scientist find signals that makes cell nucleus blow up like balloon

• This article is discussing about a certain protein which acts both an activator and a substrate in cell reproduction. The article discusses how most activators tend to start cell division. If an activator is set and cell division is done properly then there should be two identical daughter cells, but if something goes wrong it tends to form a cancer cell. This research done by a group of researchers at University of Washington is meant to be used as means of understanding treatment of cancer cells. This research might help in knowing how to slow down or stop cell division in cancer cells for good.  The article gives good amount of background information of the topic it was going to discuss such  as actually describing what mitosis does then proceeding into the new findings. This article is helpful  for researchers who are trying to figure a way to slow or stop cell division of cancer cells. The researchers can actually target certain substrates or activators which are causing the cells to divide continuously. The article acknowledges the fact that the research is still active. This article goes more in-depth into what is currently the topic at hand. We know that cancer cells tend to metastasis and spread all over the body, but this article helps with actually narrowing down what is actually causing that spread and the uncontrolled cell division.(5)   

Article #3: Researchers Find New Translocation; Weak Spots in DNA Lead to Genetic Disease

• This article is talking about certain disorder or genetic deficiencies in children of parents with no sign of any genetic disorder. The study was conducted in Children’s Hospital of Pennsylvania led by researcher Beverly S. Emmanuel. This was to see why certain children with disorders such down syndrome have parents who are OK. The research group focused mainly between chromosome 8 and 22. The concluded that a recurrent translocation between chromosome 11 and 22 are causing these disorder to happen. The test had 11 patients who had a dislocation between chromosome 8 and 22 and were exchanged with other to ultimately to get a child with an extra chromosome. Certain trisomy is fatal in early life or cause lifelong damages while the ones between 8 and 22 are less severe. A lot of people go unrecognized with the Emmanuel Syndrome due to mild effects in the people who have it. This article gave a background of on trisomy as well as the events surrounding around the experiment conducted by the researchers. It gives a proper conclusion as to what they know from the experiment and gives an implication of what to do next into learning more about genetic disorders. We learned in class that trisomy is due to having an extra chromosome and this article show an insight into how certain people get that extra chromosome. There is more work to be done in the study of genetic disease, but the researchers at the hospital are getting more information into how genetic disorders are made.(7)

External Website Links:

1. Arizona Biology: Mitosis
2. In-Depth Description of Meiosis 
3.  Meiosis Vs. Mitosis Comparison Chart
4.  Stanford Hospital: Mitosis/Meiosis Chromosome Abnormality
5.  Scientists Find Signals That Make Cell Nucleus Blow Up Like a Balloon
6. New findings on chromosome changes in tumor cell
7. Researchers find new translocation; Weak spots in DNA leads to genetic disease  

References:

• 1http://www.youtube.com/watch?v=Cg4ASxSKH2o
• http://www.youtube.com/watch?v=qjjHKDn12qI&feature=player_embedded
• 2ScienceDaily. Retrieved December 5, 2010, from http://www.sciencedaily.com­ /releases/2010/10/101014121111.htm
• 3 ScienceDaily. Retrieved December 5, 2010, from http://www.sciencedaily.com­ /releases/2010/11/101109081608.htm
• 4http://www.pbs.org/wgbh/nova/miracle/divi_text.html 
• http://www.phschool.com/science/biology_place/biocoach/meiosis/overview.html
• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Meiosis.html
• http://www.cellsalive.com/meiosis.htm