Cell Growth and Division Cell Cycle Mitosis Cytokinesis

Cell Growth  Rather than growing indefinitely, cells divide  Keeps cell size small Maintains a large surface area to volume ratio Does not put too many demands on DNA More efficient transport of materials in and out

Cell Size Surface Area/Volume Ratio: 631.5

Cell Division  Process by which a cell divides into two new identical cells Called daughter cells Reduces cell volume Each daughter cell receives a full set of genetic instruction

Reasons for cell division  Growth of organism  Reproduction  Renewal  Repair

Genetic Material  Each new cell needs a copy of DNA  Usually, DNA is found in an uncondensed form  chromatin (spread out and unfolded)  Before division, DNA is copied and chromatin condenses to form chromosomes (easier to separate)

Genetic Material

Chromosomes  After duplication, consist of two sister chromatids held together by a centromere Each chromatid = chromosome “X” = doubled

Number of chromosomes is specific to an organism…  Human – 46  Cat – 38  Dog – 78  Mouse – 40  Frog – 26  Fruit Fly – 8  Potato – 48  Corn – 20  Carrot – 18  Yeast - 32

The Cell Cycle  Series of events as cells grow and divide  Consists of: Interphase (resting stage) Mitosis (nuclear division) Cytokinesis (cytoplasm division)

Cell Cycle

Interphase  Preparation time between cell divisions  Cell is in resting phase and performing regular cell functions  Usually majority of cell cycle (about 90%)  Consist of three phases: G1 – Growth of cell; normal activities S – “Synthesis;” DNA is replicated G2 – More growth and prep for division

M phase of Cell Cycle  Consists of mitosis and cytokinesis  Mitosis – nuclear division Chromosomes are separated PMAT – prophase, metaphase, anaphase, and telophase  Cytokinesis – cytoplasm division Two new cells formed

Mitosis  Prophase Chromatin condenses  chromosomes Spindle forms  Involves centrioles in animal cells Spindle fibers attach to chromosomes Nucleus and nucleolus break down

Mitosis  Metaphase Chromosomes line up along the center of the cell Hint: metaphase  middle

Mitosis  Anaphase Centromeres split Sister chromatids are separated and pulled to opposite sides of the cell

Mitosis  Telophase Chromosomes  chromatin Nuclei and nucleoli reform Spindle breaks down

Cytokinesis  Cytoplasm is divided  In animals, cell membrane draws inward (cleavage furrow) until the cytoplasm is pinched in two  In plants, cell plate forms which will later develop into the cell wall  Usually occurs at the same time as telophase

Cytokinesis

Regulating the Cell Cycle  Not all cells move through the cycle at the same rate Nerve and muscle cells don’t usually divide after initial development Skin, digestive, and bone marrow cells grow and divide rapidly Depends on need or cell type

Regulators  Cyclins – proteins that regulate the timing of the cell cycle determine when cells will divide  Many other proteins regulate the cell cycle by responding to signals both inside and outside the cell

Uncontrolled Cell Growth  Cancer – when cells lose the ability to control their own growth “defective” cells divide uncontrollably and form tumors May break from tumors and spread to other parts of the body (metastasis) Can disrupt normal activity and cause tissue damage

Cancer  Benign- when abnormal cells remain at original site usually removable and noninvasive Not yet compromising to tissues  Malignant – invasive enough to impair organs or tissues

Causes of Cancer  Often due to lack of regulation by proteins  Could be triggered by: Smoking Radiation exposure Viral infections Toxic materials Genetics  Many still unknown