Lec 21_06_09_04

Lec 21_06_09_04 - Chapter 20 Regulation of the Eukaryotic...

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Chapter 20 Regulation of the Eukaryotic Cell Cycle. During the cell cycle chromosomes are duplicated and one copy of each duplicated chromosome segregates to each of two daughter cells. Regulation of the cell cycle is critical for the normal development of multicellular organisms. Loss of control can lead to cancer. Biochemical, genetic and recombinant DNA technology have all contributed to understanding various aspects of the eukaryotic cell cycle. These studies have revealed that cell replication is primarily controlled by regulating the timing of two key events: chromosome replication and segregation. The master controller of these events are a small number of heterodimeric protein kinases that contain a regulatory subunit (cyclin) and catalytic subunit (cyclin dependent kinase). These kinases regulate the activities of multiple proteins involved in DNA replication and mitosis by phosphorylating them at specific regulatory sites activating some and inhibiting others to coordinate activities. 13.1 Overview of the Cell Cycle and its Control. Figure 21-1 shows the cell cycle is divided into four major phases. In cycling somatic cells, chromosome replication occurs during the S (synthesis) phase. After progressing through the G 2 phase cell begin the complicated process of mitosis called the M phase which again is divided into several stages. Chromosomes condense during the prophase period of mitosis (M phase) by folding into tight loops of the 30 nm chromotin fiber attached to the chromosome scaffold and are visible by light microscopy. Sister chromotids produced by DNA replication during the S phase remain attached at the centromere and align in the center of the cell during metaphase. Sister chromotids separate during anaphase and move to opposite poles of thee mitotic apparatus or spindle segregating single chromotides to each daughter cell. In most cells the nuclear envelope breaks down into multiple small vesicles early in mitosis and reforms around the segregated chromosomes as they decondense during telophase, the final mitotic stage. Cytokinesis marks the physical division of the cytoplasm yielding two daughter cells. The Golgi complex and endoplasmic reticulum also vesiculate during mitosis and reform in each daughter cell after cell division. In fact, the nuclear envelope retracts into the ER. During interphase the mitotic apparatus consisting of a football shaped bundle of MTs with a star shaped cluster called the spindle. During metaphase a multiprotein complex the kinetochore assembles at each centromere. The kinetochores of each sister chromatid then associate with MTs coming from opposite spindle poles. During anaphase sister chromatids separate and are initially pulled by motor proteins along the spindle MTs toward opposite poles then are further separated as the mitotic spindle elongates. During telophase the nuclear envelope reforms around the segregated chromosomes
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This note was uploaded on 09/18/2008 for the course BIM 202 taught by Professor Simon during the Spring '06 term at UC Davis.

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Lec 21_06_09_04 - Chapter 20 Regulation of the Eukaryotic...

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