Cell Division Biology 1107 Exam 2 Study Guide Nick Buitrago Cell Division new cells arise by splitting preexisting cells o Meiosis v Mitosis Gametes v somatic cells How do cells replicate o Growth wound repair asexual reproduction Chromosome single long DNA double helix wrapped around proteins histone for eukaryotic cells o Gene length of DNA that codes for specific protein or RNA Prior to mitosis each chromosome is replicated o Chromatid each of DNA copies in replicated chromosome Centromere connection of chromatids Sister chromatids As mitosis starts chromosomes condense from long thin filaments into compact structures that can be moved around cell At the end of mitosis one of the chromosome copies is distributed to each Growing cells cycle between dividing phase mitotic M phase and non of two daughters cells dividing phase called interphase o No changes in nucleus can be seen in interphase and chromatin is relaxed o Timing of phases depend on cell type and growth conditions Interphase contains two gap phases no DNA synthesis o G1 G2 o S phase each chromosome consists of two genetically identical sister chromatids attached at centromere Mitosis o Prophase Chromosomes condense and first become visible in microscope Microtubule organizing center MTOC are centrosome make up of a pair of centrioles Spindle Apparatus produces mechanical forces that o i Move chromosome o ii Pull chromatids apart Polar microtubules o Do not attach Kinetochore microtubules o Pull chromosomes to the poles of the cell during mitosis o Remain stationary but minus grows while the plus end disassembles Tubulin subunits are lost o Dyneins and kinetochore motor proteins are attached to kinetochore crown Astral microtubule o Organize centrosomes Spindle form around chromosome o Prometaphase Nuclear envelope breaks down Nucleolus disappears Kinetochore microtubules from each mitotic spindle attach to one of the sister chromatids of each chromosome Attaches at kinetochore o Metaphase Formation of mitotic spindle is complete Motor proteins on the kinetochore microtubules pull each chromosome in opposite directions causing them to line up Imaginary plane formed by this called the metaphase plate o Anaphase fiber Centromeres split and sister chromatids are pulled by the Replicated chromosomes split into two identical sets of replicated chromosomes As soon as they are no longer attached at the centromere sister chromatids become daughter chromosomes o Telophase Nuclear envelope begins to form Mitotic spindle disintegrates Chromosomes begin to de condense When two independent nuclei have formed mitosis is complete o Cytokinesis typically occurs immediately after mitosis Cytoplasm divides to form two daughter cells own nucleus and complete set of organelles Different cell types undergo cytokinesis differently Plants o Vesicles are transported from the golgi apparatus to the middle of the diving cell Vesicles fuse to form cell plate Animals fungi slime molds o Ring of actin and myosin filaments contracts inside the cell membrane causing it to pinch inward in a cleavage furrow Bacteria o Do NOT undergo cytokinesis but divide via fission Similar to animal cytokinesis Control of Cell Cycle o Variation in the length of G1 phase is responsible for different in cell cycle length Skipped in rapidly dividing cells Non dividing cells get stuck G0 Nerve and muscle cells o Rate of cell division also respond to changes in environmental factors o Mitosis promoting factor MPF present in cytoplasm of M phase cells and induces mitosis in all eukaryotes Composed of protein enzymes kinase that catalyzes the transfer of a phosphate from ATP to target protein Cyclin dependent kinase Cdk is only active when bound to the cyclin subunit Cyclin subunit functions as a regulatory protein After it binds to cyclin MPF s Cdk subunit becomes phosphorylated at two sites then inactive Late in G2 enzymes cause one of the phosphate groups to Changes shape activating Starts mitosis During anaphase enzymes ubiquitins degrade MPF s drop off cyclin Many other proteins are involved in regulating the cell cycle o Three distinct cell cycle checkpoints G1 Cell size Nutrient availability Social signals from other cells Health of DNA o p53 protein either pauses the cell cycle or initiates apoptosis programmed cell death if DNA is damaged Tumor suppressor Damage can lead to uncontrolled cell division Stops growing if chromosome replication has not proceeded properly or if DNA is damaged G2 Mitosis Anaphase o Not split into chromatids until all kinetochores attach to spindle M G1 Cancer common sometimes lethal disease caused by cells that divide o Do not fully separate arrested in M presence of MPF prevents cytokinesis uncontrollably o Can spread through bloodstream or lymphatic vesicles Become malignant when they can detach and spread metastasis o Defects Make the proteins required for cell growth active when they Prevent tumor suppressor genes from shutting down the cell should not be cycle o Tumor forms when one or more cells in a multicellular organism begin to divide uncontrollably Benign versus malignant o Defects in G1 Social control is based on growth factors polypeptides or small proteins released by cells that stimulate division in other cells Cancer cell divide without growth factors o Rb protein enforces G1 checkpoint keeping the cell in G0 Excessive growth factors override inhibitory effects EF2 triggers genes needed for S phase blocked by Rb protein later gets phosphorylated by MPF o Cyclin over production i excessive growth factor ii Cyclin production in absence of growth signal Meiosis During sexual reproduction a sperm and an egg unite to form a new individual through a process called fertilization Meiosis is nuclear division that precedes the formation of gametes Karyotype is the number and types of chromosomes present in an o Zygote organism Sex chromosomes determine sex of individual all others are autosomes Chromosomes that are the same shaped size are homologous chromosomes or homologs o Carry same genes but may contain different alleles Chromosomes carry genes a section of DNA that influence one or more hereditary traits in an individual o Different versions of a gene are called alleles A cell s ploidy n 2n 3n indicates the number of each type of chromosome present o Haploid n o Diploid 2n One parental one maternal Meiosis I o 2n parent n daughter cells o Early Prophase I Homolog pairs come together in a pairing process called synapsis