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Chapter 12~ The Cell Cycle
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3 Key Roles of Cell Division Reproduction Growth and development Tissue renewal and repair
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Cell division vocabulary Genome Cell’s genetic information Made of several DNA molecules each one containing and enormous amount of information Chromosomes are condensed coils of DNA that are found in eukaryotic cells right before cellular division takes place Types of Eukaryotic cells Somatic (body cells) cells Diploid (2n): 2 sets of chromosomes Gametes (reproductive cells): sperm and egg cells Haploid (1n): 1 set of chromosomes
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Chromosomes components Chromosomes are tightly coiled chromatin Chromatids: replicated strands of a chromosome Each chromosome has two sister chromatids Centromere: narrowing “waist” of sister chromatids ( where they are most closely attach together) Kinetochore: Structure of proteins associated with specific a section of chromosomal DNA at the centromere
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Chromatin structure is based on levels of DNA packing Histones ( 1 st level) Proteins- DNA wraps around the histone moleulces Nucleosomes ( 2 nd level) Beads on a string- The whole complex of DNA and several histone proteins 30- nm fiber ( 3 rd level) String of nucleosomes coil to from chromatin fiber Looped Domains ( 4 th level) 30- nm fiber further folds and creates looped domains Chromosome ( 5 th level) Looped domains fold even further to produce a chromosome
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Types of cellular division Somatic cell division Mitosis: nuclear division Cytokinesis: cytoplasm division Gamete cell division Meiosis: gamete cell division
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The Mitotic Cell Cycle Mitosis ( division of somatic cells) is one part of the cell cycle of all cells Cell cycle Interphase G1- cell resting and growth S – DNA synthesis ( replication ) G2 – grows and gets ready for cell division M Phase division of the nucleus and the cytoplasm
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Mitosis and spindle formation Before mitosis can begin the spindle must be formed Centrosomes Have pairs of centrioles Centrosomes spin the spindle microtubules which will eventually pull the sister chromatids apart during anaphase
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Mitosis ( M phase of cycle) 5 Phases in mitosis Prophase Prometaphase Metaphase Anaphase Telophase and cytokinesis
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Prophase Chromosomes visible Nucleoli disappear Sister chromatids Mitotic spindle forms Centrosomes move
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Prometaphase Nuclear membrane fragments Spindle interaction with chromosomes Kinetochore develops Where spindle fibers attached to centromere of chromosome
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Metaphase Centrosomes at opposite poles Centromeres are aligned Kinetochores of sister chromatids attached to microtubules (spindle)
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Anaphase Paired centromeres separate; sister chromatids liberated Chromosomes move to opposite poles Each pole now has a complete set of chromosomes
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Telophase Daughter nuclei form Nuclear envelopes arise Chromatin becomes less coiled Two new nuclei complete mitosis
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Cytokinesis Cytoplasmic division Animals: cleavage furrow Plants: cell plate
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Control of cell cycle Cell Cycle Check Points 1. Cell Growth Check point (G1)- Checks to see if conditions are right for cell to divide. If cell gets the “okay” here it will most likely divide
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Control of cell cycle 2. DNA Synthesis Check Point ( G2)- DNA replication is checked 3. Mitosis Checkpoint- Triggers the exit from mitosis and back into the G 1 phase. If control of the cell cycle is lost you get things like cancer in which there is uncontrolled growth and division
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Control of cell cycle Controlled mostly by proteins within the cell Cyclin- dependent kinases Regulatory molecules that are proteins of two main types Protein kinases- enzymes that activate or inactivate other proteins by phosphorylating them Present at a constant concentration within the cell but will only be activated in the presence of cyclin ( other protein)
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Control of the cell cycle Cyclin-Cdk complexes MPF- Maturation promoting factor ( M- phase promoting factor) Triggers the cells passage from the G2 checkpoint into the M phase Results when cyclin that accumulated during the G2 phase meets with the Cdk to make the MPF complex MPF switches itself off by destructing the cyclin that the Cdk is attached to rendering it inactive and putting the cell back into the G1 phase
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Cell Cycle regulation Growth factors- proteins released by certain body cells Density- dependent inhibition- too many cells the cell will stop dividing Anchorage dependence
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