Cell Division and Growth Chapter 10

How large can a cell be? Is there a limit? DNA “overload” = when a cell becomes too large and an “information crisis” occurs Too difficult to exchange materials The speed of exchange is determined by the cell membrane

What determines the rate of exchange of materials? Surface area to volume ratio The larger the surface area-to-volume ratio the more materials a cell can exchange with its environment

Example problems A cube with all sides 1 cm in length A cube with all sides 2 cm in length

What happens when a cell becomes too big? 1. The cell can die. 2. The cell can divide to produce two new daughter cells (cell division)

Mitosis Process in which a cell with a nucleus divides and forms two identical nuclei. Refers to division of nucleus Cytokinesis = division of the cytoplasm Asexual Reproduction One parent Offspring identical to parent cell

Nucleus review: Control center Location of genetic material Chromatin = material of which chromosomes are composed Histones = small groups of proteins where chromatin is found Chromosome = short, thick, rod-like, chromatin structures

Chromosome structure Chromatid = each individual strand of a chromosome Centromere = region where chromatids join.

Mitosis is a continuous process which can be divided into phases.

Interphase Not considered a “phase” of mitosis. Time when a cell is between mitotic cycles Often called the “resting stage” This is NOT an accurate description

Events of Interphase: Cell is growing in size Proteins,organelles, and nucleic acids are produced Majority of a cell’s “life” Prepares for mitosis Chromosomes and centrioles replicate.

Relative lifetime of a cell:

1) Prophase The double chromosomes are visible as threads that coil and contract into thick rods

Events of prophase Centrioles migrate toward opposite ends (poles) of the cell. Microtubules extend from centrioles to form asters and eventually a spindle. Toward end of prophase chromosomes begin to move to center (equator) of the cell Nuclear envelope and nucleolus disappears

Late Prophase:

2) Metaphase Centromeres line up on equator Two chromatids of each chromosome become separate chromosomes ANIMAL PLANT

3) anaphase The duplicated chromosomes move to opposite poles Microtubules help to move the chromosomes. ANIMAL PLANT

4) Telophase Chromosomes uncoil and get longer Spindle fibers disappear Nuclear membrane forms around “daughter” nuclei. ANIMAL PLANT

Review of mitosis Mitosis Movie and tutorial

Cytokinesis Division of the cytoplasm. Begins during late anaphase and finishes during telophase in animal cells.

Controlling cell division Do all cells divide at the same speed? Why do cells divide at different speeds? When do cells divide fastest during one’s life?

Regulating division Cyclins : proteins found in eukaryotic cells that regulate the timing of the cell cycle. Internal regulators: proteins that work inside the cell External regulators: proteins that respond to events outside the cell growth factors, after injury, embryological

Defined as uncontrolled cell division. If cells continue to divide over and over, eventually a mass of cells can be formed called a tumor that may interfere with normal tissuue or cellular functions.

Assignment Pages Page ,14,19,20,27,29 Page