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Chapter 1: Overview of the cell cycle
Interphase
Interphase is broken down into 3 different parts. The 5irst, and longest part of the interphase is the G1 phase. This period of growth represents the primary growth of the cell. The second longest phase, nicked the S-­‐phase, (synthesis phase) is when the cell replicates the DNA. The Third and last phase of interphase is the g2 phase. This is the time of which the cell grows and prepares for cell division(mitosis). There are various types of cells that stay in the G0 phase. The brain is the most known, as it stays in interphase for decades. Another organ that stays in the G0 phase is the eyes. After it grows to full size, it never grows again. Here’s a interesting fact: Did you know that the skin cells in human stay approximately 22 hours in interphase? It’s the longest phase, as the other phases only take a few minutes.
Here’s some interesting facts that you might have not known. Mitosis has more than one name; its also known as the M-­‐phase. Most cells stay in interphase most of its life, before dying out after mitosis.
After mitosis, the cells actually do not have any cytoplasm in it, so it has to go through cytokinesis before it can fully separate! Chapter 2
Cancer
Cell division is usually a very controlled process, but when it goes haywire, it can be fatal. Cancer is a disorder in which the cells have lost all ability to control their own rate of growth, growing abnormal cells at rapid rates. Cancer cells that we are exposed to everyday is air pollution, or more simple things like cigarrete smoke.
Chapter 3
Mitosis
Mitosis serves as the process of cell division and asexual reproduction that keeps us alive and well.
All cells, except for cells that enter the g0 phase and cells that undergo meiosis go through mitosis, as it’s the way they stay alive. There are several phases to mitosis. The 5irst phase of mitosis is the Prophase.
The Centriole pairs begin to move toward the opposite poles of the cell, and the centrioles move the chromosomes to the poles as well. Spindle 5ibers begin to extend from the centrioles, and the chromosomes form and become visible. The second phase of mitosis is Metaphase.
The Nuclear envelope begins to melt down, and eventually vanishes. Spindle 5ibers begin to stretch out and cover chromosomes, and this aligns the chromosomes to the equator of the cell.
The third phase of mitosis is Anaphase.
The spindle 5ibers begin to shorten, and pull apart the chromosomes, making chromatids, and begin their journey to the poles of the cell.
The fourth and 5inal phase of mitosis is Telophase.
The chromatids arrive at opposite poles of the cell. New nuclear membranes form around the chromatids. The Centrioles and spindle 5ibers disappear, and chromosomes stretch out into chromatin.
Cytokinesis also starts to occur, and cleavage furrow/cell plate begins to form. Then, the parent cell spilts into two daughter cells, and mitosis is completed. How many chromosomes are in a human cell, you wonder? Well, there is 46 chromosomes in a human parent cell and there is 23 in a daughter cell.
Chapter 4
Meiosis Overview
What is the purpose of Meiosis, you wonder?
It’s very simple! The purpose of meisosis is to reduce the normal diploid cells (aka, turn the two chromosomes into one per cell) to haploid cells, which are called gametes(cells with only one copy of each chromosome). We have two unique haploid cells resulting from meiosis, and they are gender speci5ic. One is called a egg(Female sex cells) and the other is called sperm (Male sex cells). Every time meiosis is gone through, one viable egg is cell is made, while 4 viable sperm cells are made. This is to keep it so human population doesn’t explode – If females could have more than one viable egg, duplets, quadruplets, and more during pregnancy would be incredibly common. Also, when a egg is fertilized, it is called a zygote. What would happen if meiosis did not occur? Disaster. The zygote would have twice as many chromosomes than it should have it should have, and since in meiosis both sperm and egg cells are haploid cells, they need to be brought together to make a diploid, aka, normal cell. If meiosis did not occur for 5ive generations, assuming anything without meiosis could survive that long, it would have over 210 different chromosomes to sort out, nearly impossible for any normal cell and it would surely kill the cell within seconds of creation, essentially making it impossible for any race to survive. This is why meiosis is so important, as it stops this from happening and keeping the ability to reproduce without massive defects.
Chapter Five
Meiosis I
Meiosis, in general, follows essentially the same path as Mitosis, but with a few variances that make ALL the difference between them.
The First stage of meiosis I is Prophase I. The chromosomes begin to pair up and they exchange DNA to form varied chromosomes. Then, the Chromosomes begin coming together, and start the process of ‘crossing over’. Then, the chromosomes begin their way to separate, going into Metaphase I. Metaphase I is when the spindle 5ibers begin to form, and they attach to the chromosomes, much like it would in mitosis. And, like in normal mitosis, the chromosomes would align acros the equator of the cell. Then, they would begin to tear apart, beginning journey to the poles of the cell. This starts Anaphase I. This phase their is identical to the Anaphase in Mitosis, as the chromosomes moves to the opposite poles of the cell.
This begins Telophase I, which is the same as mitosis. The chromosomes begin to diffuse and the nuclear envelope begins to reform, and cleavage furrow begins. Unlike Mitosis though, this is only the First phase of meiosis, as the cell still has chromosomes, and needs to go through Meiosis one more time to be perfect. It needs to have chromatin instead of chromosomes. Its now time for me to explain some of the differences in meiosis that makes this process so important for the human race’s continuity as a race. This would be the process of ‘crossing over’.
This is so important to the human race because without it, there would be no diversity in our DNA, and that would make us genetically weak, and ultimately, we would not survive to where we are today.
Chapter Six: Meiosis II
Meiosis II is the 5inal process for a sex cell. It separates each chromosome into chromatids, which is a haploid cell. The First phase of Meiosis II is Prophase II. This is exactly the same as it was in Meiosis I, but its happening in the two separate daughter cells that formed in Meiosis I at the same time. The chromosomes begin to condense, becoming visible to someone who is using a microscope.
The nuclear membrane that would be around the chromosome dissolves, leaving only the chromosomes in the cell, and spindle 5ibers would begin to form, bringing you to the familiar Metaphase II.
In Metaphase II, Spindle Fibers attach to chromosomes, and the chromosomes line up in the center of the cell, like in Meiosis I and Mitosis, and this would lead to Anaphase II.
In Anaphase II, the chromosomes centromeres would 5inally divide, and sister chromatids would move to opposite ends of the sex cell as the spindle 5ibers begin to shorten.
This would lead to Telophase II, which is when the chromosome reach opposite ends, the cleavage furrow begins in both sister cells, and a nuclear membrane forms in both cells.
The 5inal division would result in four cells, and the 5inal act of cytokinesis occurs.
Chapter Seven
Comparison of Mitosis & Meiosis
As many similarities between Mitosis and Meiosis exist, there is also three integral differences between them that make them unique to their own processes. For example, Mitosis occurs in any living breathing animal, organ, and cell on the planet. If it lives, it goes through mitosis. This isn’t the case for meiosis. Meiosis occurs only in gamete cells, or germline cells.
Mitosis has different results than Meiosis. Mitosis results in two diploid cells, and meiosis does not. Meiosis results in four separate haploid cells.
Another huge difference is that in mitosis, homologous chromosomes do not pair up whatsoever. In meiosis, the chromosomes do pair up.
And 5inally, Mitosis never, ever crosses over. In meiosis, crossing over does occur.
Mitosis’ daughter cells are very different than meiosis’ daughter cells. For one, there is only two daughter cells in mitosis. In meiosis, there is four. Mitosis’ daughter cells are diploid cells, or cells with one copy of chromosomes.
Meiosis’ daughter cells are haploid cells, which do not have chromosomes. Instead, they all have one chromatid.
URLS, AND ENDING!
All Mitosis pictures are courtesy of http://www.sparknotes.com/biology/
cellreproduction/mitosis/section3.rhtml !
All Meiosis pictures are courtesy of
http://www2.le.ac.uk/departments/genetics/vgec/education/post18/
topics/cellcycle-­‐mitosis-­‐meiosis/the-­‐cell-­‐cycle-­‐mitosis-­‐and-­‐meiosis !
THIS PROJECT WAS MADE BY
JUSTIN DESOTELL
JESSICA (PERIOD 2)
KYLE (PERIOD 2)
AND BREANNA (PERIOD 2)