Transcript File
Cell Division and the Cell Cycle The Cell Cycle • Interphase is the growth phase makes new molecules that increase the cell volume DNA is copied during this phase consists of 3 parts, G1, G2 and S • Division Stage consists of mitosis and cytokinesis Stages of Growth Phase • G1 gap 1 cell has rapid growth and carries out metabolic activity • S DNA is replicated • G2 centrioles replicate Cells are preparing to undergo division Division Stage • • • • Shortest events in the cell cycle 2phases M phase Mitosis Division of the nucleus • Cytokinesis Division of the cytoplasm Prokaryotic Cell Division • Is usually through Binary Fission • Prokaryotic chromosome is a single DNA molecule that replicates , then attaches each copy to a different part of the cell membrane. • When cells pull apart the replicates chromosomes are separated. • Following separation there are two cell of identical genetic composition Eukaryotic Cell Division • • • • • Mitosis Meiosis Cytokinesis Roles Before division can occur: Organelles must be replicated and sorted. DNA must be replicated and sorted. • Many chromosomes are involved. Chromatin Chromatids Centromere • • • • Mitotic chromosome Histones Homologues Homologous chromosomes • Haploid (1N) • Diploid (2N) What is the Function of Mitosis • • • • • • Helps organism regenerate damaged tissues Maintenance of the body Replaces cell that don’t work or dead cells Occurs in somatic or body cells New cells are identical to the previous ones Must maintain the same number of chromosomes from cell to cell What happens during mitosis • During cell division the original parent cell divides to produce 2 new daughter cells • Mitosis ensures that daughter cells contain the same number of chromosomes and genetic information as the parent cell • Body cell contains 2 copies of every chromosomes • At this point the parent cell produces 2 identical daughter cells with 46 chromosomes • Before mitosis the parent has 46 chromosomes after mitosis the new daughter cells each have 46 chromosomes • Deals only with the segregation of the chromosomes and organelles into daughter cells • Animals cells have a centriole that aid in cell division Cell Cycle and Mitosis • Rate of cell cycle • Varies with cell type • Hormones and growth factors regulate the rate. • Cancer • Interphase • Appearance of cell Stages of Mitosis • Phases • Prophase, Metaphase, Anaphase, Telophase Prophase • First of four phases • Chromatin coils and condenses into Chromosomes • Each chromosome is made up of 2 sister chromatids held together by a centromere • Spindle fibres forms • Centrioles migrate to opposite poles • nuclear membrane dissolves, • nucleolus disappears Metaphase • Second phase • Spidnle fibers attach to the centromere of replicated chromosomes • Chromatids are guided to middle of the cell with the help of spindle fibers • Chromosomes line up in middle of the cell. Anaphase • Third Phase • Centrosome splits apart • Spindle fibres help to pull apart sister chromatids. • These then move toward opposite spindle poles because the microtubules are shortening Telo-phase • Fourth and last phase • Chromatids reach opposite poles. • At this point each chromatid is called a single nonreplicated chromosome • Chromosomes unwind and become less visible. • Nuclear membrane forms around each set of chromosomes. • Spindle is dismantled and disappears. • Nucleolus reappears. • Two new cells identical to the parent cell • Opposite of prophase • Mitosis (pro-meta-ana; ciol up , line up, split up) Cytokinesis • Happens after mitosis. • It is the separation of the cytoplasm and the formation of 2 new daughter cells. • During cytokinesis the cytoplasm and all its contents divides between the two halves of the cell. • In animals: Cleavage furrow forms due to the contraction of the microfilaments of the cytoskeleton. Like a noose. Cells eventually pull apart into 2 identical cells. • In plants: A cell plate forms between the 2 new nuclei. This eventually forms a cell wall that separates 2 identical cells. Mutations affecting cell division • A mutation is a permanent change in the DNA that can change the genetic information of a gene causing it to function improperly or not at all • Caused by chemical compounds, radiation, or specific viruses • After it has occurred it will be copied in subsequesnt cell division and passed to daughter cells • Found only in the two cell produced from that parent cell • Most are insignificant because they can be replaced by normal cells • If the mutation occurs in the gene that controls the cell division process it can result in cancer ( the uncontrolled rapid growth and division of cells) Radiation Therapy and cell division • Involves directing radiation such as x-rays or gamma rays at the affected part of the body • Works by damaging the chromosomes in a cell rendering it unable to grow or divide • Healthy cells are damaged as well as cancerous cells but they can repair themselves • Used on tumours of the skin, breast, larynx and cervix • Side effects include skin inflammation, fatigue, sterility in males(testicular cancer) Chemotherapy and Cell division • Includes a course of 1 or several types of drugs used in conjunction with radiation • Some drugs attack dividing cells as they divide while other prevent division • It affects the entire body because it is used to treat cancers that are spread throughput the body such as leukemia • Side effects include hair loss, nausea, or diarreha Complete each of the following terms. • • • • • • • • • • Chromatin Interphase Mutation Chromatids Prophase Radiation Centromere Metaphase Chemotherapy Mitoitic chromosome Anaphase Histones Cytokinesis Telophase Homologues Cell Cycle Homologous chromosomes G1 Haploid (1N) G2 Spindle fibres Diploid (2N) S Sister chromatids Daughter cells