Chromosomes cellular structures consisting of one DNA molecule and associated protein molecules A eukaryotic cell membrane bound nucleus contains multiple linear chromosomes and a prokaryotic cell non membrane bound nucleus contains a single circular chromosome Chromatin coiling occurs after DNA replication and assists in visibility of chromatin fibers Meiosis cell division that produces sperm and eggs Human somatic cells contain 46 chromosomes 2 sets of 23 one from each parent Phases of the cell cycle Mitotic phase mitosis and cytokinesis Interphase G1 G2 and S phase for synthesis and duplication of cells to prepare them for division from there we enter the Mitotic phase and 2 daughter cells are produced via cell division Mitosis Interphase end of G2 phase the two centrosomes have been formed via duplication of a single centrosome Prophase the chromatin fibers become more tightly coiled becoming visible chromosomes mitotic spindle begins to form as the two centrosomes move away from each other Prometaphase the nuclear envelope begins to fragment and eventually disappears mitotic spindle microtubules begin to elongate and move towards opposite ends attaching to kinetochores also the chromatids are now very small fragments rather than long fibers Metaphase centrosomes are at opposite poles of the cell and all chromosomes are at the metaphase plate in the center of the cell Anaphase the two sister chromatids part and move toward the centromeres at the ends of the cell the cell elongates and the mitotic spindle begins to shorten Telophase Cytokinesis the daughter cells begin to form their own nuclei and cytokinesis cleaves splits them forming two daughter cells with their own set of chromosomes Plant vs animal cell cytokinesis plant cells contain an inflexible cell wall and cannot be pinched off by a cleavage furrow Binary fission in eukaryotes bacteria gave rise to mitosis Experimental data in an experiment scientists concluded that combining a cell in S phase with a cell in G1 phase would produce the G1 cell to immediately enter the S phase and begin DNA synthesis In another experiment an M phase cell was combined with a G1 cell the G1 cell would immediately begin mitosis skipping the duplication process End result fusing cells would result in both cells entering the phase of the initial cell in the cytoplasm s phase Microtubule shortening experimental data in an experiment is was concluded that the shortening of microtubules is relative to the movement of kinetochores rather than the movement of spindle poles Thus a chromosome is walked along a microtubule to the kinetochore end rather than the spindle pole end Cyclin Dependent Kinases depends on the binding with the protein cyclin to regulate cell cycle function also attaches phosphate groups to their proteins MPF a model of CDK fluctuation a cyclin CK complex triggers the cell s passage into the M phase past the G2 checkpoint During MPF if cyclin accumulation during G2 phase associates with CDK molecules the cyclin protein initiates mitosis In anaphase MPF switches itself off by destroying its own cyclin the CDK then persists until it can associate with new cyclin synthesized in the S phase and G2 phase Cyclin drops off during M phase which ultimately stops cell division Cancer cells are mutated cells that fail to undergo apoptosis and ignore the checkpoints that deny them the right to stop dividing Ras protein is a typical cancer protein that feeds cancerous cells The overconcentration of cyclin causes cells to repeat M phase and thus create cancerous cells Gene expression the process by which information encoded in DNA directs the synthesis of proteins or in some cases RNAs that are not translated into RNA and instead function as RNAs Stages of gene expression Repressed genes when the repressor binds to the operator and blocks attachment of RNA polymerase to the promoter preventing gene transcription Gene inducers inactivation of the repressor gene prevents the repressor from binding to the operator Translation the synthesis of a polypeptide using the genetic information encoded in an mRNA molecule Transcription the synthesis of RNA using a DNA template Activator proteins bind to mediator proteins which bind to promoters activators mediator proteins promoters and general transcription factors combine to form transcription initiation complex Histone acetylation one example of epigenetic phenomena promotes transcription by opening up the chromatin structure DNA methylation the addition of methyl groups reduced transcription by condensing the chromatin structure Differentiation the process by which cells become specialized in structure and function Sources of developmental information Cytoplasmic determination maternal substances in the egg that that influence the course of early development Induction contact with outside cell signals influence the cell s interior signals Determination the point at which a cell irreversibly becomes determined to function a specific way Pattern formation when cytoplasmic determinants and inductive signals contribute to the spatial arrangement of tissues and organs and their specific characteristics positional information triggers pattern formation Bicoid a cytoplasmic determinant regulatory transcription factor the bicoid protein in highly concentrated at the anterior end of the mature egg and migrates to the posterior end Anterior appendages form where the concentration of bicoid protein is highest is transcribed by nurse cells and translated during fertilization contain egg polarity genes or maternal effect genes if mother has mutant genotype the offspring will have mutant phenotype Three reasons a proto oncogene may become an oncogene amplification of a proto oncogene increasing the number of copies of proto oncogenes movement of DNA within the genome translocation if the translocated proto oncogene ends up near a promoter transcription could increase causing an oncogene and point mutations in the promoter or enhancer or in the coding sequence of a proto oncogene Tumor suppressor genes the proteins these genes code for prevent uncontrolled cell growth they also inhibit cell division Ras gene mutations works with a growth factor receptor on the plasma membrane to a cascade for protein kinases leads to production of hyperactive Ras protein that triggers the kinase cascade causing increased cell division cancer P53 gene a tumor suppressor gene that promotes the synthesis of cell cycle
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