Mitosis Student Notes PDF

Human life cycle, cell division processes and cycles, mitotic cell division, and cancer Cell division results in cell proliferation (i.e., increase in number) which may be bene cial or harmful. fi Human Life Cycle Requires mitotic/meiotic divisions Human ≈ 1012 human cells (man...

Human life cycle, cell division processes and cycles, mitotic cell division, and cancer Cell division results in cell proliferation (i.e., increase in number) which may be bene cial or harmful. fi Human Life Cycle Requires mitotic/meiotic divisions Human ≈ 1012 human cells (many more bacterial, protist, and fungal cells) Somatic cells (2n) —body cells that divide mitotically (repair, growth, etc.) Germ cells (2n) in gonads ultimately divide meiotically to form gametes (n) Gametes (n) fuse during syngamy (aka fertilization) to form zygote (2n) Zygote (2n) divides mitotically to form somatic/germ cells in o spring ff Genetic load (ploidy) Diploidy (2n) —two sets; 2n=46 Haploidy (n) —one set; n=23 Human Life Cycle Requires mitotic/meiotic divisions Two forms of cell division in human life cycle: Mitosis —proliferates genetic clones Germ cells (2n) ➟ more germ cells (2n) Zygote (2n) ➟ adult (2n) Meiosis —reduces genetic load producing genetically unique cells Germ cells (2n) ➟ gametes (n) Genetically unique gametes (n) combine during syngamy (fertilization) ➟ zygote (2n) (combination of two sets of chromosomes from two different cells ↑ genetic diversity)  ▼Sea urchin development: 2-cell stage (Image: Evelyn Spiegel and Louisa Howard doi:10.7295/W9CIL39782) Mitotic Cell Division Has many roles to play Mitotic cell division —proliferates genetic clones; responsible for: Maintain supply of germ cells Growth/development into an adult Wage an immune response Repair damaged tissues Basal cells Cell turnover (e.g., RBCs, epidermal cells) Grow ephemeral tissues (e.g., placenta) ▲Epidermis (super cial layer) with dermis fi  Interphase Cell Cycle Cells divide within cell life cycle G1 S Interphase (~90% of cell’s life) —time for growth, metabolism, normal cell function G 1 —checkpoint (🚦); continue or not? C G2 M S —DNA synthesis (i.e., DNA replication) G 2 —checkpoint (🚦) M phase — nal meta/ana checkpoint (🚦) M phase Cytokinesis Mitosis (M)—division of parent nucleus (2n) via five phases into into two daughter nuclei (2n) Cytokinesis (C)—cytoskeleton constricts partitioning cytoplasm, organelles, and daughter nuclei into separate daughter cells If does not occur, forms multinucleate cell ▲HeLa cells dividing (Image: Dylan T. Burnette, Ph.D., Vanderbilt University School of Medicine) fi  Checkpoints —cell may arrest cycle if something is wrong (if not, cell Cell Cycle may become cancerous) To prevent propagation/accumulation of mutations Cytokinesis Mitotic Cell Division An overview Diploid (2n) cell replicates its chromatin and condenses it into replicated chromosomes Half of a replicated chromosome = sister chromatid; connected via a centromere Sister chromatids separate and are partitioned into two daughter cells (2n) Results in two diploid (2n) daughter cells that are genetic clones of each other (and the former parent cell)  Mitotic Cell Division Interphase Prophase Prometaphase Metaphase Anaphase Telophase Cell ‣ Centrioles ‣ Nucelar ‣ Spindle helps ‣ Spindle ‣ Daughter duplicates: migrate… envelope move helps nuclei reform ‣ chromatin ‣ Replicated disorganizes replicated separate ‣ Chromosomes chromatin ‣ Spindle forms chromosomes sister de-condense ‣ centrioles to cell equator chromatids condenses ‣ Cytokinesis to poles Kinetochores Motor complexes move chromosomes Sister chromatids/daughter chromosomes move to cell poles via two mechanisms: Spindles not connected to replicated chromosomes elongate cell Kinetochores complexes near centromeres motor along spindle bers (microtubules) microtubules depolymerize in their wake fi  Cellular Differentiation Stem cells proliferate/di erentiate Even though mitosis generates genetic clones, di erent cells express di erent genes so they vary in size, shape, and function This specialization process is called cellular di erentiation; many di erentiated cells no longer divide/proliferate Stem cells of varying di erentiation (totipotent, pluripotent, multipotent) proliferate via mitotic cell division within the cell cycle then, di erentiate into more specialized cells Hematopoietic stem cells di erentiate into blood cells such as RBCs ▲Cellular di erentiation (Image: Haileyfournier Creative Commons Attribution-Share Alike 4.0 International) RBCs lose nucleus and do not divide ff ff ff ff ff ff ff ff ff Cancers More Info: National Cancer Institute Cancerous cells have 60+ gene mutations in proto-onco and tumor-suppressor genes (e.g., p53, BRCA1) no longer respond to cell cycle control (fail to arrest at checkpoints) avoid apoptosis escape normal tissue boundaries (by degrading ECM and cell-cell junctions) forming tumors that may metastasize via blood/lymph vessels Breast cancer most common (excluding non-melanoma skin cancers)