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Chapter 15 Blog: Eukaryotic Cell Cycle, Mitosis, and Meiosis (Robert)

Page history last edited by Robert Canuel Jr. 13 years ago

In the first section of this page, you will write a daily summary of that day's class.  For example your first entry should be titled 9/3/10.  You should then write a one or two paragraph summary of that day's topic.  In the second section, you are required to add two items (link to a website, video, animation, student-created slide show, student-created PowerPoint presentation) and one journal article pertaining to a topic in this chapter.  A one-paragraph summary must accompany each item describing the main idea and how it applies to the lecture topic.  Please see the PBWorks help guide for assistance embedding video and other items directly in the page.  I will also produce a how-to video on using tables to wrap text around items and other useful tips.  Please see the syllabus for organization and grading details.

 

A.  Daily Blog

 

     Chapter 15 is all about cell division. Normally, humans have 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes. These can be identified using a karyotype. Half of the 23 pairs of chromosomes are obtained from the father and the other half is obtained from the mother. Thus the diploid number of chromosomes for humans is 46 and the haploid number is 23. Having a diploid amount of chromosomes means the organism has 2 sets of homologous chromosomes one from each of the parents. Haploid means the organism has only one set of chromosomes. The cell is usually in the G0 phase of its life until it needs to divide. When the cell is getting ready to divide it copies its entire genome in the S(ynthesis) phase. Then follows the G2 phase where the cell makes proteins for cell division. Now for cell division. For the somatic cells of a human the division is mitosis.

     Mitosis consists of the steps: prophase, metaphase, anaphase, telophase and cytokinesis(this one has exceptions). In prophase, the chromosomes condense into their familiar X-shaped forms with its own sister chromatid and the nuclear envelope dissipates. The chromosomes line up at the metaphase plate and the centrioles form spindle fibers that are attached to the kinetochores in metaphase. During anaphase the fibers pull the sister chromatids apart to the poles of the cell and. . . Telophase reforms the nuclear envelope around each set of chromosomes. This is usually followed by cytokinesis, which is the division of the cytoplasm.

     Now for the human gametes, these are formed in a reduction division known as meiosis. In meiosis the cell divides twice so each resulting gamete has one set of the original 23 pairs of chromosomes. So that means the cell undergoes all the steps in mitosis twice. Therefore scientists name the metaphase in the first division "metaphase I" and the metaphase in the second division "metaphase II". In prophase I, the chromosomes form tetrads with their sister chromatids and their homologues. At this time a chromosome and its homologue may exchange DNA in an event called crossing over. The DNA exchanged is similar and thus there is no loss of genes. Then during metaphase I the tetrads line up randomly and independently and the centrioles pull the homologues apart from each other to the poles. Then follows anaphase I, telophase I and cytokinesis. Meiosis II is basically the same as mitosis except for a haploid cell. Just so Dr. Weber doesn't dock points on me I will restate that this is for HUMAN cells. I understand that some organisms live most of their life in the haploid state, exemplia gratia fungi. These organisms are called haploid-dominant for that reason. The other is diploid-dominant like humans. The last part of this chapter talks about the differing amount of chromosomes in an organism. There are, besides diploid and haploid, other numbers of chromosomes such as polyploid and aneuploid. These are a result of a failure to separate in meiosis thus forming an organism with too much or too little DNA. This can have a beneficial or harmful effect on the organism.

 

B.  Useful Materials

 

Items:

 

Item 1

http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookmito.html

     Here is a website that explains cell division in prokaryotes, called binary fission, and mitosis in eukaryotes. It does the same thing the book does and it has pictures for those who just can't stand a wall of text. The bottom of the site has links to other sites that could also help with understanding mitosis

 

Item 2

     This video is about meiosis. Once more this is for those who can stand a wall of text. The video shows crossing over and the stuff that was talked about in class about meiosis.

 

Article:

 

Megakaryocyte lineage specific class VI β-tubulin suppresses microtubule dynamics, fragments microtubules, and blocks cell division.

     This interesting article talks about an isotope of a tubulin molecule that is involved in cytokinesis. It says that when this tubulin combines with other tubulin molecules it causes the microtubule to become unstable and fragment. Therefore cytokinesis is never started and the cell continues onto the G1 phase. This article specifies that these fragments of the microtubules have been found in platlets and the large megakaryocyte.

 

 

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