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:902.52.52.52.5

Interphase

Prophase

Metaphase

Anaphase

Telophase

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 257-259

Page 257-258 1-10,14,19,20,27,29

Page 259 1-12