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Chapter 8

BIOL 1000 Chapter 8 - Cell Cycles.docx

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BIOL 1000
Jennifer Steeves

8.1 – The Cycle of Cell Growth and Division: An Overview • Mitosis – Nuclear division, in a somatic (body) cell, that produces daughter nuclei that are the exact genetic copies of the parental nucleus  Multi-celled Eukaryotes – The basis for growth and maintenance of body mass  Single-celled Eukaryotes – Reproduction • Eukaryotic Chromosomes – The linear nuclear unit of genetic info, consisting of a DNA molecule and associated proteins • DNA Replication and the duplication of chromosomal proteins convert each chromosome into two Sister Chromatids  Exact copies of a chromosome duplicated during replication 8.2 – The Cell Cycle in Prokaryotic Organisms • Prokaryotic Cells undergo a cycle of Binary Fission producing 2 daughter cells  Coordinated cytoplasmic growth  DNA replication  Cell division • Binary Fission  Asexual Reproduction  Produces exact copies of parent  Can result in rapid population growth • Replication of the bacterial chromosome consumes most of the time in the cell cycle  Begins at a single site called the origin through reactions catalyzed by enzymes located in the middle of the cell • Once the origin of replication (ori) is duplicated, the two origins actively migrate to the two ends of the cell • Division of the cytoplasm then occurs through a partition of cell wall material that grows inward until the cell is separated into two parts 8.3 – Mitosis and the Eukaryotic Cell Cycle • Chromosomes contain different genes and are of differing lengths • When a cell isn’t dividing the chromosomes are thin and form a network in the nucleus  Individual chromosomes are only recognizable during Mitosis • Diploid – An organism or cell with two copies of each type of chromosome in its nucleus  Most Eukaryotes are 2n • Haploid – An organism or cell with only one copy of each type of chromosome in its nuclei  Microorganisms are n • Ploidy – The number of chromosome sets of a cell or species • Mitosis and Interphase constitute the Mitotic Cell Cycle  Mitosis occurs in 5 Stages Interphase • The first stage of the mitotic cell cycle • The cell grows and replicates its DNA before undergoing mitosis and cytokinesis • G 1hase – The initial growth stage of the cell cycle in eukaryotes  The cell makes proteins and other types of cellular molecules but not nuclear DNA  Usually the only phase that varies in length for a given species  Also the stage in which many cells stop dividing – G 0 • S Phase – The phase of the cell cycle in which DNA replication occurs  Most mammalian cells take about 10-12 hours • G2Phase – The phase of the cell cycle during which the cell continues to synthesize proteins and grow; in order to divide into two cells  Most mammalian cells take 4-6 hours • During all the steps the chromosomes are relatively loose, but organized, in the nucleus • G Phase – The phase of the cell cycle in eukaryotes in which many cell types stop 0 dividing  E.g. In humans, cells of the nervous system normally enter G once0they are fully mature • One of the hallmarks of cancer is the loss of normal control in the G1/S phase transition Prophase • Duplicated chromosomes within the nucleus condense from a greatly extended state into short, compact, rod-like structures - sister chromatids • The nucleolus becomes smaller and eventually disappears in most species  Shutdown of all types of RNA synthesis, including the ribosomal RNA made in nucleolus • The mitotic spindle in the cytoplasm begins to form between the two centrosomes as they start migrating toward the opposite ends of the cell  The complex of microtubules that orchestrate the separation of chromosomes  Forms the Spindle Poles – One pair of centrosomes in a cell undergoing mitosis from which bundles of microtubules radiate to form the part of the spindle from that pole Prometaphase • Nuclear membrane/envelope breaks down and disappears • Microtubules elongate and centrosomes are pushed toward the poles; forming Mitotic Spindle • The kinetochore microtubules of the mitotic spindle attach to the kinetochore of each chromatid at the centromere • Kinetochore – Specialized structure consisting of proteins attached to a centromere that mediates the attachment and movement of chromosomes along the mitotic spindle • Centromeres – A specialized chromosomal region that connects sister chromatids and attaches them to the mitotic spindle • Microtubules that do not attach to kinetochores overlap those from the opposite spindle pole • The chromosomes shuffle until they align in the centre of the cell Metaphase • The spindle reaches its final form and the spindle microtubules move the chromosomes into alignment at the spindle midpoint/cellular midline  Also called the Metaphase Plate • Centrosomes are at the poles and microtubules are at fu
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