Cell Division Chapter 10

Limits to Cell Growth DNA Overload Exchanging Material The larger a cell becomes, the more demands the cell places on its DNA Exchanging Material The cell has trouble moving enough nutrients and wastes across the cell membrane if the cell is too big. Surface Area:Volume ratio can’t be too small

Cell Cycle

Cell Cycle Interphase (inter- means “between”) M phase G0 phase G1 phase – Cell growth S phase – DNA replication G2 phase – preparation for cell division Cells are in interphase most of the time. M phase Mitosis: prophase, metaphase, anaphase, telophase, cytokinesis G0 phase Cells that cannot divide like nerve cells, red blood cells, and cardiac cells

Prophase Chromosomes condense into sister chromatids Plant cells in prophase Prophase Chromosomes condense into sister chromatids Chromatids are joined by a centromere Centrioles appear and form mitotic spindle Nucleolus disappears and nuclear envelope dissolves Longest phase of mitosis (50-60%) Pair of centrioles

Anatomy of a Chromosome

Metaphase Centrioles on opposite ends of the cell Animal cell Plant cell Centrioles on opposite ends of the cell Microtubules of mitotic spindle attach to the centromeres Chromosomes line up across the middle (equator) of the cell

Anaphase Sister chromatids separate Early anaphase (plant) Late anaphase (plant) Sister chromatids separate Chromosomes migrate to opposite ends of the cell Anaphase (animal)

Telophase Chromosomes begin to disperse Nuclear envelopes reform Plant cell Animal cell Chromosomes begin to disperse Nuclear envelopes reform Mitotic spindle breaks apart

Cytokinesis Difficult to distinguish from telophase Animal cell Plant cell Difficult to distinguish from telophase In animal cells the cell membrane pinches in forming two daughter cells In plant cells a cell plate forms between the daughter nuclei and a new cell wall forms at the cell plate

Mitosis animations Cells alive http://www.cellsalive.com/mitosis.htm Vcell http://vcell.ndsu.edu/animations/mitosis/movie-flash.htm PBS http://www.pbslearningmedia.org/resource/tdc02.sci.life.stru.dnadivide/mitosis/

Controls on Cell Division When cells are touching each other, they tend to stop growing and dividing. Cyclins are proteins that regulate when a cell divides. Internal regulators respond to environment within the cell. External regulators respond to environment outside of the cell.

Cancer Uncontrolled cell growth Cancer cells smother normal cells Caused by smoking, exposure to radiation or certain chemicals, some viruses Cancer cells smother normal cells Treatment options Surgery to remove tumor Radiation therapy to halt cell division Chemotherapy to halt cell division