Cell Division

Mutations and Cancer Mutation = random changes to the base sequence of genes A mutation may change a proto-oncogene (produces normal cell cycle control)  oncogene (produces uncontrolled cell cycling) Mutagens = agents that produce changes in genes involved in controlling the cell cycle, causing uncontrolled cell division. Chemical (asbestos, dioxins, tobacco smoke, etc.) X-rays or short-wave UV light Metastasis = movement of cells from a primary tumor to set up secondary tumors in other parts of the body.

Mitosis Check out onion root tips undergoing mitosis. Can you determine what phase the cell is at? Online Onion Root Tips http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html

Why cells divide? Large cells have a reduced SA:Vol ratio Growth of organism Replace dead, damaged or infected cells Asexual reproduction

Stages of the cell cycle interphase G1: growth, protein synthesis, increase in the number of mitochondria and/or chloroplasts S: DNA replication G2: growth, protein synthesis, preparation for mitosis/cytokinesis mitosis = nuclear division prophase metaphase anaphase telophase cytokinesis = cellular division

Terms Chromosome = DNA + proteins Chromatid = one of two copies of DNA Sister chromatids = two identical copies of DNA Centromere = region on chromosome that joins sister chromatids Spindle fiber = microtubules that move chromosomes during cell division Centriole = microtubule organizing center

Prophase Chromosomes condense by supercoiling, becoming visible to microscopic view Centrioles move to opposite poles Nucleolus disappears Nuclear membrane disappears Microtubular spindle apparatus forms at each pole

Metaphase Spindle microtubules attach to chromosome centromeres Chromosomes move to the equator

Anaphase Centromeres split as spindle microtubules pull chromatids to opposite poles (after centromeres split, sister chromatids are known as sister chromosomes) Sister chromosomes move to opposite poles as microtubules shorten

Telophase Sister chromosomes have arrived at poles Spindle disappears Centrioles replicate Nuclear membrane reforms and becomes visible Nucleolus becomes visible Chromosomes decondense, becoming chromatin