Genetics_Primer - I. Summary of the Cell Cycle ~

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Summary of the Cell Cycle ~ Cell Cycle - the amount of time spent in each stage of the cell cycle (G1, S, G2 & M phase) is biochemically controlled There are 4 distinct phases that make up the cell cycle. Three are growth phases and are collectively called Interphase ; the fourth is a period of division, therefore, referred to as M- Phase. During Interphase , cells typically double in size. The first part of interphase is called G 1 (Gap 1). This is a period marks a maintenance of basic cell activities and takes anywhere from 1 hour to several days depending on the cell type. This is followed by the S phase (synthesis); during this period, which typically lasts 9 hours, DNA is replicated ; this means that a copy of the DNA is made. The last stage of interphase is called G 2 (Gap 2). Here, the cell prepares to divide; certain proteins, called spindle proteins, necessary for cell division are made at this time. G2 takes about 3 hours to complete. Additionally, organelles such as mitochondria, plastids, and ribosomes double in number. After interphase is the M phase. Two critical events occur at this time. The first is mitosis , which is the division of the nuclear material. During mitosis, 2 sets of chromosomes are distributed to opposite ends of the cell and two daughter nuclei form. The other event, which happens near the end of mitosis, is cytokinesis . Here, the cytoplasm divides and the two daughter nuclei are separated into two daughter cells . The other cell constituents (organelles) are partitioned into the daughter cells also. Replication of chromosomes to prepare for cell division [Mitosis] - Relatively fool proof process (1 out 100,000 replication events leads to a mistake [mutation]) - The error rate is controlled by evolution (some species have a higher mutation rate) - Harry’s slides shows a series of cell stages o Interphase cells – this is when Replication occurs (chromosome replicates all its genetic information. The result is two sister chromatids joined by a centromere) o Active division during the M-phase of cell cycle includes [Prophase, Metaphase, Anaphase, Telophase] II. SUMMARY OF MITOSIS ~ Mitosis = nuclear division where the chromosome number of resulting daughter cells is the same as the original cell that underwent Mitotic divison. At the beginning of mitosis, the DNA has already been doubled (replicated) and is packaged into chromosomes made up of pairs of sister chromatids [sister chromatids are joined together at a central point called the centromere, thus forming the replicated chromosomes]. The first part of mitosis is called Prophase . During early prophase, the chromosomes condense and the nucleoli disappear. The mitotic spindle continues to form in the cytoplasm - this is a web like structure made of microtubules. Its role is to suspend and, later during mitosis, move the chromosomes. They arise at microtubule-organizing centers, called centrioles in animal cells. The organizing centers (there are two) spin out microtubule fibers and move to opposite ends
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This note was uploaded on 03/30/2009 for the course BIO G 110 taught by Professor Wayne,r. during the Spring '07 term at Cornell University (Engineering School).

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Genetics_Primer - I. Summary of the Cell Cycle ~

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