Cell Division Chapter 10 Limits to Cell Growth

Cell Division Chapter 10

Limits to Cell Growth • DNA Overload – 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 • Interphase (inter- means “between”) – G 1 phase – Cell growth – S phase – DNA replication – G 2 phase – preparation for cell division – Cells are in interphase most of the time. • M phase – Mitosis: prophase, metaphase, anaphase, telophase, cytokinesis • G 0 phase – Cells that cannot divide like nerve cells, red blood cells, and cardiac cells

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

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

Animal cell Cytokinesis 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/movi e-flash. htm PBS http: //www. pbslearningmedia. org/resource/t dc 02. 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 – 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