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

Page history last edited by Nicole Lee 13 years ago

A.  Chapter 15 Blog

     Have you ever wondered what the world be like without cell division?  Well to be completely honest, not much.  Cell division is a crucial part of life.  Cell division is process of reproduction of the cells.  This process is highly regulated and uses 2 techniques in Eukaryotic cells.  These two processes are known as mitosis and meiosis.  Chapter 15 mostly discussed The Eukaryotic Cell Cycle, Meiosis, and Mitosis.   

     One issue that the cell must undergo is having the chromosomes becoming properly replicated AND sorted to new daughter cells, all while keeping under a great amount of timing and accuracy.  To start things off, what are Eukaryotic chromosomes?  Eukaryotic chromosomes always occur in sets.  These ‘sets’ are also composed of a variety of chromosomes.  Cytogenetics is the field of genetics involving microscopic examination of cell division and chromosomes.  Humans have 23 different chromosomes and most eukaryotic cells contain TWO sets of chromosomes.  Each human has a total of 46 chromosomes (one set being from the mother and one from the father).  However, if the organism has two sets of chromosomes, it is known as diploid.  ALWAYS REMEMBER: only most of our cells are diploid.  However, gamete cells (sperm and egg cells) are known as haploid.  What is haploid you may ask?  Haploid cells only have one set of chromosomes.  If the organism is diploid, the members of the pair of chromosomes are known as homologues.  Homologues are similar, but they are usually not identical.    

     So now that we have gone over some of the basics of cell division you may be asking, what is cell division already?!  Well, before we get into THAT part of the explanation we must go through the steps firstJ.  How does everything occur?  It occurs through a series of phases (G1, S, G2, and M).  The end product of this is two daughter cells.  The original diploid cell had three pairs of chromosomes (meaning that they have six individual chromosomes).  During the S phase, the chromosomes get replicated to yield twelve chromatids.  By the end of the process, the daughter chromatids have six chromatids.

     An example that the class was given stated that liver cells of an animal have 24 chromosomes, then how many sperm cells does the animal have (without knowing the species of the animal)?  The answer is 12.  If you don’t remember, liver cells are somatic.  To be completely honest, when this question was given to the class I did not know the answer or how to find it so once Dr. Weber went over the explanation as to how to solve it I became much more familiar with the subject.

     The class also touched base with the reasons why the cell decides to divide in its lifetime.  The cells divide usually over two factors (external factors and internal factors).  External factors are caused from environmental conditions and through signaling molecules.  Internal factors occur when the cell cycle controls the molecules and through check points.  How you may ask what some types of check point proteins are?  Well, in a nut shell, check point proteins can be cyclin or cyclin- dependent kinases.  These are responsible for advancing a cell through the phases of the cell cycle.  However, the amount of cyclin varies throughout the cell.  Kinases controlling the cell cycle must bind to cyclin to become active.

     So back to the subject, what is mitotic cell division?  Mitotic cell division is a process in which a cell divides to produce two new daughter cells.  The process of mitotic cell division utilizes meiosis and cytokinesis.  Meiosis is the division of the nucleus into two nuclei. Meiosis occurs through a series of phases.  These series of phases include prophase, prometaphase, metaphase, anaphase, and telophase.  Here is a little information about each one of them:

·         Prophase is when the chromosomes condense and the nuclear membrane begins disassociate

·         Prometaphase is when the mitotic spindle is completely formed

·         Metaphase occurs when the chromosomes are lined up along the metaphase plate (halfway between the poles).

·         Anaphase is when the connections amongst the pairs of sister chromatids are broken causing them to move to opposite poles

·         Telophase occurs when the chromosomes have reached their poles (the nuclear membrane re-forms)      

·        Cytokinesis occurs when the mother cell divides into the two daughter cells

Those steps are EXTREMELY crucial.  However cytokinesis is so important because asexual reproduction and the maintenance of multiple cells.  

     Another important part of meiosis is the process of crossing over.  Crossing over occurs when there is an exchange of genetic information because homologous pairs.  Why is this so important? Because it increases the amount of genetic variation!  Another important factor about the meiosis process is meiosis I and meiosis II.  In meiosis I, the homologues (we discussed this) are split into different cells.  In meiosis II, the chromatids are separated into different cells.  The class’ overview of chapter 15 helped me understand the topic of the eukaryotic cell cycle, mitosis and meiosis.





B.  Useful Materials

This first video shows a group of students performing a cell cycle song.  This video is extremely helpful in the sense that it goes through the cell cycle and it discusses the cell theory.  all known living things are made up of cells.  All cells come from pre- existing cells through division.  This video talks about how all organisms utilize cell division.  This song is catchy and helped me understand the cell cycle and why it is so crucial for humans and all organisms for that matter.  


This second video is a song about mitosis.  The video goes through the explanation of mitosis in the cell.  Mitosis is cell division, where the nucleus of the cell divides, resulting in two sets of identical chromosomes. Mitosis is accompanied by cytokineses in which the end result is two completely separate cells called daughter cells. There are four phases of mitosis: prophase, metaphase, anaphase and telophase.


C.  Article


This article talks about how feed back control is an important process for every living organism.  This article relates to the topic of this chapter because feedback control is a crucial factor in external and internal changes.  Like my blog discusses, the cells only divide over those two factors, whether it is Internal factors which occur when the cell cycle controls the molecules and through check points.  or whether they occur from External factors (environmental conditions and through signaling molecules).  This article was extremely interesting and helpful toward my understanding of chapter 15.  




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