Week 3

Week 3 - Week 3: Lecture 1 Weve gone through prophase and...

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Week 3: Lecture 1 We’ve gone through prophase and metaphase last week. We are going to continue mitosis with anaphase. Anaphase : The reason for this elaborate dance becomes apparent. The cell must have a mechanism to distribute one of every chromosome to its daughter cells but if there is an error of 2 or 0, the cell risks death or cancer. In anaphase, the microtubules/centrioles rip each chromosome apart at the centromere. The microtubules will start contracting. Four chromosomes will go up and four will go down so there is virtually no chance of error (The error rate is small but not zero). The chromatids become separated. Each chromatid becomes a chromosome. There are 8 chromosomes, 8 chromatids and 8 DNAs. Telophase: An actin ring pinches off the nucleus and the cell to separate cell and to separate the two nuclei. Nuclear membrane starts reforming. We still have one cell until we reach G1 of the next cell cycle. There are 8 chromosomes, 8 chromatids and 8 DNAs. Finally, in G1, we have two cells with 4 chromosomes, 4 chromatids and 4DNAs.
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You must be able to tell the number of each at each point in the cell cycle, IT WILL BE ON THE EXAM!!! GOAL OF MITOSIS: Produce daughter cells, which are identical to each other as well as the mother cell, to produce 2n diploid cells. These two cells are independent with independent choices - growth or differentiation. They can both go into growth phase, they can both differentiate or one of each. With growth, the cell goes into G1 and the cell cycle. But with differentiation, the cell goes into G0, a reversibly quiescent state. Cells that make the wrong choice by entering G1 when they should not are cancer cells. Meiosis Meiosis is similar to mitosis except for one very important modification. In mitosis the mother cell divides into two exact replicas of genetic material. The chromosomes in the daughter cell are exactly the same as the chromosomes in the mother cell. In meiosis, however, the goal is to form germ cells. Meiosis forms haploid gametes rather than diploid daughter cells. Each of the germ cells will not be identical to the mother cell. Each of the germ cells will have half the number of chromosomes as the mother. The process of meiosis is much slower than mitosis. It can takes day or years to complete the process of meiosis. The cell cycle is exactly the same for meiosis as for mitosis through G1, S and G2 but instead of entering the Mitosis phase the cell cycle will enter the meiosis phase. In mitosis G1, S and G2 make up interphase. Interphase then goes into prophase. In meiosis interphase leads to prophase I. Meiosis will consist of prophase I, metaphase I, anaphase, I telophase I, prophase II, metaphase II, anaphase II and telophase II. To differentiate between mitosis and meiosis all of the phases of meiosis have numbers after them (prophase I, metaphase II, etc) whereas mitosis phases do not have numbers (prophase, metaphase, etc). Like in mitosis, entering prophase I is when the DNA condenses into tightly packed chromosomes. Once these
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This note was uploaded on 09/26/2008 for the course BIO 340 taught by Professor Pratt during the Spring '08 term at ASU.

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Week 3 - Week 3: Lecture 1 Weve gone through prophase and...

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