Cell Growth and Division

Ch. 10

Why are cells so small?????????

10-1 Cell Growth

1. DNA Overload – larger cells place more demands on the DNA.

2. Exchanging Materials – diffusion of materials takes time.

◦ As the ratio of surface area to volume gets small, the cell membrane has trouble diffusing materials fast enough.

Limits to Cell Growth

Cell Size

Surface Area (length x width x 6)

Volume (length x width x height)

Ratio of Surface Area to Volume

Ratio of Surface Area to Volume in Cells

As a cell grows, if it doesn’t do something about these two problems the cell will die…..

So before this occurs, the cell divides.◦ This prevents DNA overload and increases surface

area for diffusion of materials.

The Dilemma…

Cell Division10-2

Asexual reproduction Growth and development Repair and maintenance

Why do cells divide?

What is a chromosome?

Genetic information (DNA) within the nucleus of each cell..

The number of chromosomes is species specific.

◦ Hedgehog – 88◦ Chicken – 78◦ Horse – 64◦ Humans = 46◦ Rat – 42◦ Starfish – 38◦ Snail – 24◦ Koala - 16◦ Fruit flies = 8

Chromosomes

The genetic information must be copied before cell division.◦ This process is called replication.

This insures each daughter cells gets a full set of genetic information.◦ Without this the cell could not survive.

Chromosomes

The “life cycle” of a cell. Two main phases.◦ Interphase = period of time between divisions;

growth and preparation for division. Longest phase.

◦ M phase = cell division. Shortest phase. Two parts: Mitosis (karyokinesis) – nuclear division Cytokinesis – cytoplasmic division

The Cell Cycle

M phase

G2 phase

S phase

G1 phase

The Cell CycleSection 10-2

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Mitosis and Cytokinesis

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Mitosis and Cytokinesis

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Mitosis and Cytokinesis

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Mitosis and Cytokinesis

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Mitosis and Cytokinesis

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

CentrioleChromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Mitosis and Cytokinesis

The cell membrane pinches in.

Animal Cell cytokinesis

A cell plate forms.

Plant cell cytokinesis

Onion Root Tip

http://www.youtube.com/watch?feature=player_embedded&v=VGV3fv-uZYI

http://www.youtube.com/watch?v=aDAw2Zg4IgE&feature=player_embedded

http://www.youtube.com/watch?v=pOsAbTi9tHw&feature=player_embedded

Cell division video

Mitosis produces two genetically identical cells.◦ THEY HAVE THE SAME # AND TYPE OF

CHROMOSOMES.◦ THEY HAVE THE SAME GENETIC INFORMATION

(GENES).◦ THERE IS NO GENETIC VARIATION. THEY ARE

CLONES.

End Result

http://nobelprize.org/educational_games/medicine/2001/cellcycle.html

Cell Cycle Game

Regulating the Cell Cycle

10-3

Not all cells have the same length cell cycle…◦ Nerve and muscle cells – very long; rarely divide◦ Skin and blood cells – short; often divide

CellCycle

What controls the length of the cell cycle??????

Contact inhibition – ◦ When cells come in contact with each other, they

usually stop growing.◦ Cells at the site of an injury lose contact inhibition

and begin growing. This repairs the injury.

Controls on Cell Division

Control of Cell DivisionSection 10-3

Cyclins – proteins that regulate the timing of the cell cycle in eukaryotic cells.◦ Internal regulators – proteins that allow the cell

cycle to proceed in response to events going on in the cell.

◦ External regulators – proteins that speed up or slow down the cell cycle in response to events outside the cell.

Cell Cycle Reglators

A sample of cytoplasm is removed from a cell in mitosis.

The sample is injected into a second cell in G2 of interphase.

As a result, the second cell enters mitosis.

Effect of Cyclins

Section 10-3

Cancer – a disorder in which cells do not respond to normal regulatory signals.◦ Cancer cells have no contact inhibition.◦ Cancer cells divide uncontrollably and produce

masses called tumors. Benign tumors no longer are growing. Malignant tumors are currently growing and may

spread. Cancer therapy involves chemotherapy,

radiation treatments and surgical removal.

Uncontrolled Cell Growth

Carcinogens – agents that cause the development of carcinomas (tumors).◦ Radiation – x-rays, uv rays◦ Chemicals – cigarette smoke, asbestos◦ Genetics

Cancer therapy involves chemotherapy, radiation treatments and surgical removal.

Uncontrolled Cell Growth