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Bio 1A03 chp11.docx

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McMaster University
Joe Kim

Chapter 11- The Cell cycle Mitosis Cell division functions -reproduction (uniceullular) -growth, development, and tissue repair (multicellular) M Phase and interphase: -Interphase is nondividing phase -Cells spend most of their time in Interphase -interphase chromosomes not usually visible Discovery of Cell Cycle -researchers used radioactive isotopes to trace chromosomes (phosphorous and thymidine) -use of isotopes known as autoradiography -figured out there was an S phase (synthesis phase) How long does S phase last? experiment 1.Feed radioactive thymidine to cells growing in culture. Only cells in synthesizing will have label 2. Wash extra thymidine out 3.Spread cells and expose to photographic emulsion -S phase is about 8 hours long and there is a lagging gap between S phase and M phase How does Mitosis Take Place? -Eukaryotic chromosomes normally exist as extremely long, threadlike strands consisting of DNA associated with globular proteins called histones -DNA-protein material combined called chromatin -Dna copies in a replicated chromosome is called chromatid. Chromatids from same chromosome called sister chromatids -chromatids joined by centromere Cell cycle-Interphase g1 phase: cell growth and duplication of organelles S phase: DNA synthesis (chromosomes replicate) g2 phase: cell growth and duplication of organelles continues to build the protein "machinery" Why doe GAP phases exists? -before mitosis occurs, the parent cell must be large enough size and must have required organelles, so that daughter cells will operate normally What is the G0 phase? -the nondividing state What are examples of cells in G0? -nerve cells that are mature, and muscle cells -Note that in other cells, such as liver cells, they can go back from G0 back into the cell cycle. This is triggered by external cues (ex.growth factors released upon injury) Prophase: -visible in light microscope -formation of mitotic spindle (spindle fibres pull chromosomes into daughter cells) -centrosome: microtubule organizaing centre containing pair of centrioles -spindle either move to opposite side or form on opposite sides Prometaphase: -nucleous dissapears and nuclear envelope fragments --spindle fibres attached to chromosome -kinetochore: each chromosome has two where spindle fibres attach (one on each side) Metaphase: -chromosomes line up along a line called metaphase plate -mitotic spindle formation compete Anaphase: -sister chromatids pulled apart to create identical chromosomes -kinetochore spindle fibres begin to shorten Telophase: -nuclear envelope begins to form around set of chromosomes . -mitotic spindle fades away Cleavage furrow: Fold in membrane of animal cell during cytokinesis due to actin filaments sliding Cell plate: Line in between cells due to vessicles from golgi building up there How do Chromosomes moves during Mitosis? - the tubulin subunits of the kinetochore microtubules are depolymerized (lost) from the kinetochore ends - motor proteins, such as dynein attach and detach along the kinetochore microtubule’s length, this results in chromosome movement -protein in kinetecore catalyze the loss of tubulin subunits at the plus end , while motor proteins moves towards the minus end. experiment: -Use flourescent labels to make the metaphase chromosomes flurosce blue and microtubules yellow 2.Photobleach a section of microtubules 3.
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