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Problem of the day: Which picture shows the type of membrane receptor used by hormones, such as testosterone? How do you know?
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Cell Receptors: b Receptors in the plasma membrane Water soluble signaling moleculesWater soluble signaling molecules Bind to receptor proteins that span the membraneBind to receptor proteins that span the membrane b Intracellular receptor proteins Found in the cytoplasm or nucleus of target cellsFound in the cytoplasm or nucleus of target cells Signal molecule (ligand) can pass throught he plasma membrane (hydrophobic, nonpolar)Signal molecule (ligand) can pass throught he plasma membrane (hydrophobic, nonpolar)
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Chapter 12: The Cell Cycle You must know: b The structure of the replicated chromosome b The cell cycle and stages of mitosis b The role of kinases and cyclins in the regulation of the cell cycle b The role of mitosis in the distribution of genetic information
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The Cell Cycle Mitosis Mitosis b Most cell division results in genetically identical daughter cells (not meiosis) b Cell cycle-life of a cell from the time it is first formed from a dividing parent until the time it divided. b Genome (DNA) must be copied first b Mitosis: growth and repair (diploid) b Meiosis: formation of gametes (haploid)
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Role of Cell Division b Reproduction, growth, and repair b Daughter cells are clones b Cancer is uncontrolled cell division-a problem with enzymes that control the cell cycle due to mutations in genes that code for these enzymes.
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Parts of a chromosome Each chromosome is one very long linear DNA molecule that carries several hundred to a few thousand genes. When a cell is not dividing, each chromosome is in the form of a long thin chromatin fiber The picture to the left shows a duplicated chromosome-one. When the chromatids separate there will be 2 chromosomes.
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How Prokaryotic Cells Divide b Bacteria and Archaea b Binary fission b Single chromosome that consists of circular DNA molecule b NOT MITOSIS
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Key Terms in Cell Division b Genome: cell’s genetic information b Somatic (body cells) cells b Gametes (reproductive cells): sperm and egg cells b Chromosomes: DNA molecules b Diploid (2n): 2 sets of chromosomes –somatic cells are diploid b Haploid (1n): 1 set of chromosomes-gametes are haploid b Chromatin: DNA-protein complex b Chromatids: replicated strands of a chromosome b Centromere: narrowing “waist” of sister chromatids b Mitosis: nuclear division b Cytokinesis: cytoplasm division b Meiosis: gamete cell division
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The Cell Cycle Highly regulated with checkpoints, which determine the ultimate fate of the cell Interphase (90% of cycle) G1 phase~ growth G1 phase~ growth S phase~ DNA replication S phase~ DNA replication G2 phase~ preparation for cell division G2 phase~ preparation for cell division Mitotic phase Mitosis~ nuclear division Mitosis~ nuclear division Cytokinesis~ cytoplasm division Cytokinesis~ cytoplasm division Cancer results from disruptions in cell cycle control.
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Interphase b 90% of the cell cycle b G 1 phase-cell functioning as a normal cell b S phase-synthesis phase, occurs when DNA is replicated b G 2 phase-cell disassembles cytoskeleton, begins formation of spindle proteins b G o some cells never progress past this phase (nerve cells and skeletal muscle cells)
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Mitosis-passes a complete genome from the parent cell to daughter cells. b Prophase b Prometaphase b Metaphase b Anaphase b Telophase
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Prophase b Chromosomes visible b Nucleoli disappear b Sister chromatids b Mitotic spindle forms b Centrosomes move
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Prometaphase b Nuclear membrane fragments b Spindle interaction with chromosomes b Kinetochore develops
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Metaphase b Centrosomes at opposite poles b Centromeres are aligned b Kinetochores of sister chromatids attached to microtubules (spindle)
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Anaphase b Paired centromeres separate; sister chromatids liberated b Chromosomes move to opposite poles b Each pole now has a complete set of chromosomes
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Telophase b Daughter nuclei form b Nuclear envelopes arise b Chromatin becomes less coiled b Two new nuclei complete mitosis
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Cytokinesis b Cytoplasmic division b Animals: cleavage furrow b Plants: cell plate
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G 0 Phase b When a cell specializes, it often enters into a stage where it no longer divides, but it can re-enter the cell cycle when give appropriate cues b Non-dividing cells may exit the cell cycle, or hold at a particular stage in the cell cycle
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Molecular Control of Cell Cycle- internal and external signals Molecular Control of Cell Cycle- internal and external signals b Major checkpoints: G1, G2 and M phase b G1 most important: if doesn’t get signal-goes to G-0 b Kinases: protein enzymes that control cell cycle; only active when connected to cyclin proteins=Cdk b Cyclin + Cdk = MPF b Anaphase- MPF switches off- starts process that leads to destruction of cyclins
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Regulation of the Cell Cycle Regulation of the Cell Cycle b Molecular control system drives the cycle b Consists of a set of checkpoints b Checkpoints integrate internal and external information b Synchronized by rhythmic changes in the activity of cdks (protein/enzyme comlexes) MPF-maturation promoting factor: a protein complex required for a cell to progress from late interphase to mitosis; active form = cyclin + protein kinase
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Duration b Interphase: 12-30 hours b Prophase: 1-2 hours b Metaphase: 5-15 minutes b Anaphase: 2-10 minutes b Telophase: 10-30 minutes
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The Mitotic Spindle b Microtubules b Assembly begins in centrosome b 2 types: kinetochore and nonkinetochore microtubules b Kinetochore microtubules separate and organize chromosomes b Nonkinetochore microtubules elongate cell b Centrioles: MTOC
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Regulation by external factors: Regulation by external factors: b Growth factors b Density-dependent inhibition-crowded cells stop dividing b Anchorage dependence- to divide cells must be attached to a substratum b Cancer cells do not exhibit these properties
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Cancer b Cells do not respond normal to control mechanisms b Make their own growth factors b Abnormal cell cycle b Unusual number of chromosomes possible b Aberrant metabolism b Lost attachment to neighboring cells and to ECM b Transformation-process that converts normal cells to cancer cells
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Cancer, cont’d. b Tumor-mass of abnormal cells within otherwise normal tissue b Benign tumor-abnormal cells remain at the original site b Malignant tumor-cells spread and invade normal tissue; impair function of one or more organs. “Cancer.” b Metastasis-when cells separate from a malignant tumor and enter blood/lymph
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HeLa cells b Henrietta Lacks (August 1, 1920 – October 4, 1951)[1] (sometimes erroneously called Helen Lane or Helen Larson) was an African American woman who was the unwitting source of cells from her cancerous tumor, which were cultured by George Otto Gey to create an immortal cell line for medical research. This is now known as the HeLa cell line.[2]
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