BIO 1120 bios 1120
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This 5 page Class Notes was uploaded by Perry Klemanski on Thursday February 11, 2016. The Class Notes belongs to bios 1120 at Western Michigan University taught by David Rudge in Winter 2016. Since its upload, it has received 126 views. For similar materials see Principles of Biology in Biological Sciences at Western Michigan University.
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Date Created: 02/11/16
Chapter 9 (Part One) Cell cycle a)G1 Phase This is the portion of the cell cycle just after division, but before DNA synthesis. During this time the cell grows by producing proteins and organelles. b)S Phase DNA synthesis (or replication) occurs during this phase. At the beginning of the phase, each chromosome is single. At the end, after DNA replication, each chromosome consists of two sister chromatids. c)Interphase Typically, this phase accounts for 90% of the cell cycle. It is a time of high metabolic activity. The cell grows by producing proteins and organelles, and chromosomes are replicated. d)G2 Phase This third sub-phase of interphase is a period of metabolic activity and growth. During this phase the cell makes final preparations for division. e)Mitotic Phase (M) Cell division occurs during this short phase, which generally involves two discrete processes: the contents of the nucleus (mainly the duplicated chromosomes) are evenly distributed to two daughter nuclei, and the cytoplasm divides in two. f)Mitosis This is when division of the nucleus occurs. The chromosomes that have been replicated are distributed to two daughter nuclei. g)Cytokinesis This is the step in the cell cycle when the cytoplasm divides in two. Cell division consists of two processes: mitosis and cytokinesis. Mitosis — division of the nucleus and its chromosomes— is divided into five phases: prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis is followed by cytokinesis, when the cytoplasm splits to form two separate daughter cells. Mitosis & Cytokinesis Interphase – Contains two centrosomes, each of which may contain a pair of centrioles. In the nucleus, the chromosomes have been replicated during S phase, but are still dispersed in the form of chromatin. One or more nucleoli are present. Prophase – The nucleoli disappear and chromatin fibers coil up to become chromosomes. Each chromosome consists of two identical sister chromatids, joined at the centromere. Microtubules grow out from the centrosomes, initiating formation of the mitotic spindle. Prometaphase (Part of prophase) – The nuclear envelope breaks up. Some of the spindle fibers reach the chromosomes and attach to centromeres. Other microtubules overlap with those coming from the opposite pole. Metaphase – The mitotic spindle is fullyformed, and the microtubules attached to centromeres move the chromosomes to the metaphase plate (Middle), an imaginary plane equidistant from the poles. Anaphase – The two centromeres of each chromosome come apart, separating the sister chromatids. Once separated, each sister chromatid is considered a daughter chromosome. Motor proteins of the centromere "walk" the daughter chromosomes along the spindle microtubules toward opposite poles, and the microtubules shorten. At the same time, the spindle microtubules not attached to chromosomes lengthen, pushing the two poles farther apart and elongating the cell. Telophase – Nuclear envelopes form around the identical sets of chromosomes at the two poles of the cell. The chromosomes uncoil and nucleoli appear in the two new nuclei. Meanwhile, cytokinesis begins, splitting the cytoplasm and separating the two daughter cells. Animal cells (Cytokinesis) - Cytokinesis (Splitting) begins with the formation of a cleavage furrow. At the site of the furrow, a ring of microfilaments contracts, much like the pulling of drawstrings. The cell is pinched in two, creating two identical daughter cells. Plant cells (Cytokinesis) – Cytokinesis (Splitting) begins when vesicles containing cell-wall material collect in the middle of the cell. The vesicles fuse, forming a large sac called the cell plate. The cell plate grows outward until its membrane fuses with the plasma membrane, separating the two daughter cells. The cell plate's contents join the parental cell wall. The result is two daughter cells, each bounded by its own continuous plasma membrane and cell wall. Interphase Prophase Prometaphase Metaphase Anaphase Telophase & Cytokinesis
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