10 – 2 Cell Division10 – 2 Cell Division

MitosisMitosis

ChromosomesChromosomes DNA is passed on in DNA is passed on in

chromosomes chromosomes Every organism has a specific # Every organism has a specific #

of chromosomes: of chromosomes:

fruit flies 8 fruit flies 8

humans 46humans 46

Before division called sister Before division called sister “chromatids”“chromatids” Chromatids are attached with a Chromatids are attached with a

centromerecentromere and become … and become …

Chromosomes Chromosomes are only are only visible during cell divisionvisible during cell division

The Cell CycleThe Cell Cycle

During the cell cycle, a During the cell cycle, a cell grows, prepares for cell grows, prepares for division, and divides to division, and divides to form 2 daughter cells, form 2 daughter cells, each of which then each of which then begins the cell cycle begins the cell cycle again.again.

1. Interphase1. Interphase = growth = growth 2. Mitosis2. Mitosis = division = division

Events of the Cell CycleEvents of the Cell Cycle InterphaseInterphase

Period of growthPeriod of growth Hereditary material is in the form of Hereditary material is in the form of

chromatinchromatin 3 stages:3 stages:

GG11 - “growth” - “growth” Increase in cell size in # of organelles, and Increase in cell size in # of organelles, and

in # of proteinsin # of proteins SS – “synthesis” – “synthesis”

DNA replication (chromatin is doubled)DNA replication (chromatin is doubled)

GG22 – “growth” – “growth” Continued cell growthContinued cell growth

nucleolus

chromatin

centrioles

Mitosis BeginsMitosis Begins

Mitosis is when a Mitosis is when a cell divides into two cell divides into two new cells.new cells.

Mitosis is one of the Mitosis is one of the shortest parts of a shortest parts of a cells life.cells life.

However, it has the However, it has the most stages.most stages.

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Mitosis (1. prophase)Mitosis (1. prophase) MitosisMitosis – period of cell – period of cell

divisiondivision 4 stages:4 stages:

ProphaseProphase – “prepare” – “prepare” Longest phase of mitosisLongest phase of mitosis Chromatin coils up and Chromatin coils up and

forms chromosomesforms chromosomes Duplicated chromosmes Duplicated chromosmes

are made up of 2 are made up of 2 identical sister identical sister chromatids connected at chromatids connected at the centromeresthe centromeres

Sister chromatid

centromere

IdenticalSisterchromatid

Mitsosis (1. prophase)Mitsosis (1. prophase) Prophase (continued)Prophase (continued) Nucleolus and nuclear membrane Nucleolus and nuclear membrane

fade away, causing the nucleus to fade away, causing the nucleus to disappear.disappear.

Centrioles move to opposite ends of Centrioles move to opposite ends of the cellthe cell CentriolesCentrioles – cylindrical structures made – cylindrical structures made

of microtublesof microtubles Spindle fibersSpindle fibers form between the form between the

centriolescentrioles SpindleSpindle – Pulls the sister chromatides – Pulls the sister chromatides

apart.apart.

*the spindle attaches to the *the spindle attaches to the chromosome at the centromere*chromosome at the centromere*

spindle

centriole

Mitosis (2. Metaphase)Mitosis (2. Metaphase)

MetaphaseMetaphase “middle” “middle” Chromosomes attach Chromosomes attach

to the spindle fibers to the spindle fibers at their centromereat their centromere

Chromosomes line Chromosomes line up along the middle up along the middle of the cell (equator)of the cell (equator)

Mitosis (3. Anaphase)Mitosis (3. Anaphase)

AnaphaseAnaphase – – “apart”“apart” Sister Sister

chromatids are chromatids are pulled apart by pulled apart by centrioles.centrioles.

Mitosis (4. Telophase)Mitosis (4. Telophase) TelophaseTelophase – “tear into two” – “tear into two”

Chromatids reach the opposite Chromatids reach the opposite sides (pole) of the cellsides (pole) of the cell

Chromosomes uncoil or unwind Chromosomes uncoil or unwind (chromatin)(chromatin)

Spindle fibers begin to break Spindle fibers begin to break downdown

Nucleolus reappearsNucleolus reappears New nuclear membrane forms New nuclear membrane forms

around each new set of around each new set of chromosomeschromosomes

Plasma membrane begins to Plasma membrane begins to separate into 2 new nucleiseparate into 2 new nuclei

Cytokinesis Cytokinesis

Division of cytoplasmDivision of cytoplasm In animals: “cleavage In animals: “cleavage

furrow” pinches the furrow” pinches the plasma membrane to plasma membrane to divide the cytoplasmdivide the cytoplasm

In plants: “cell plate” In plants: “cell plate” forms to divide the forms to divide the cytoplasmcytoplasm

Cell division-again!Cell division-again!

http://www.youtube.com/watch?v=Q6ucKWIIFmg