Chapter 8

Cells must divide forGrowthRepair

Cells cannot just continue to grow larger for two reasons:Exchanging materials

The surface area of the cell membrane must be large enough to support the volume of the cell.

Otherwise, the cell struggles keeping up with the exchange rate of food, oxygen and water across the membrane.

Information overloadToo many demands on the DNA to get its

information where it is needed.

Mitosis-The process by which a cell divides, forming

two “daughter” cellsThese daughter cells are identical to the

parent cell

Which cells ?Eukaryotic somatic (body) cells undergo

mitosisProkaryotic cells go through a process called

binary fission

ChromosomesMade up of DNA wrapped tightly around

histone proteinsDNA + histones = chromatin fiber and looks

like “beads on a string”During mitosis chromatin condenses and

coils to form chromosomes

Chromosome:Sister chromatids- Each side of a duplicated

chromosomeCentromere- Center of a chromosome, holds

sister chromatids together

Chromosome number varies for each speciesHumans= 46 Cat= 38Fruit fly= 8

The cell cycleMitosis is part of the cell’s life cycleThis cycle includes the following stages:

InterphaseMitosisCytokinesis

Interphase The longest phase of the cell cycleThe cell prepares to divide3 phases, or checkpoints, in Interphase

Phases of InterphaseG1 - intense cell growth, cells contents

duplicatedS - DNA is replicated (copied)G2 - more growth and final preparation for cell

divisionG0- cell enters this phase when something is

wrong and it either can’t or won’t divide. Ex: unstable environment, DNA was copied incorrectly, more cells not needed at that time

The Cell Cycle

After a cell goes through all the checkpoints, it is ready to divide!

The Mitotic phase of the cell cycle includes

ProphaseMetaphaseAnaphaseTelophase

ProphaseNuclear envelope disappearsChromatin condensesChromosomes are first visibleCentrioles split and move to opposite sides of

the cell

Prophase

Prophase

MetaphaseChromosomes line up in the middle of the

cell (equator)

Spindle fibers connect to chromosomes at the centromere

Metaphase = Middle

Metaphase

Metaphase (plant cell)

AnaphaseSister chromatids pulled apart to opposite

sides Spindle fibers shortenAnaphase = Away, or Apart

Anaphase

Anaphase

TelophaseTwo sets of genetic information on either side

of the cellNuclear envelope reforms around each setChromosomes no longer visible (unravel into

chromatin again)

Telophase

After mitosis is complete, the cell has one thing left to do- split! (cytokinesis)

CytokinesisSplitting of the cytoplasmForms two new distinct “daughter” cells Two cells are genetically identicalIn animals- Cell membrane “pinches off”In plants- Cell plate forms

CytokinesisIn animals: Cell membrane “pinches off”

In plants: Cell plate forms

Video linkshttp://www.youtube.com/watch?v=VlN7K1-

9QB0

http://www.youtube.com/watch?v=nPG6480RQo0&feature=related

THE END