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Cell Size

• Why not just one large cell?Why not just one large cell?• Difficult to get nutrients in Difficult to get nutrients in

and waste outand waste out

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Phases of The Cell Cycle

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G1,S, and G2 are known together as Interphase.

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Somatic cell cycle • G1 phase- Gap phase, cell

undergoes growth.• S phase- DNA synthesis• G2 phase- Gap phase.

Preparation for Mitosis. Organelles are produced.

• M phase- Cell division (Mitosis and cytokinesis)

Interphase

Regular Cells

Sex cells are

called gamete

s

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G1 Phase

•Cell growsCell grows

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S Phase• Chromosomes

Condense• Chromosomes

are inherited genetic information

• Chromosomes are made up of DNA

• Can only be seen when cells are dividing

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S Phase• Chromosomes Chromosomes

replicate-or copy replicate-or copy is madeis made

• The two copies The two copies areare

• --attached together attached together at a point called a at a point called a centromerecentromere..

• -are called sister -are called sister chromatidchromatid..

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GG2 2 PhasePhaseOrganelles must be Organelles must be replicated (copied)replicated (copied)

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M PhaseM PhaseTwo parts:Two parts:1.1.Nuclear divisionNuclear division

– MitosisMitosis2.2.Cytoplasmic DivisionCytoplasmic Division

– CytokinesisCytokinesis10

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MitosisMitosis• Nuclear Division.• Nucleus divides into two new nuclei

Mitosis keeps the number of chromosomes constant from one cell generation to the next.

• In eukaryotes, it is the main process by which growth and tissue repair is accomplished.

• Mitosis is also the main process by which single-celled and many multi-celled eukaryotes reproduce asexually.

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4 Steps of Mitosis (PMAT)•  Prophase: Chromosomes condense and attach to

the spindle fibers at their centromere.• Nuclear Membrane breaks down.

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Steps of Mitosis (PMAT)•   Prophase: Prophase: Centrioles move to opposite sides of Centrioles move to opposite sides of

the cell and organize the spindle fibersthe cell and organize the spindle fibers

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Metaphase:Metaphase: Chromosomes attach to spindle

fibersand line up in the middle of the

cell

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Anaphase: Chromosomes separate-Move to opposite sides of the cell

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Telophase• Nuclear Envelope reforms

There are now TWO nuclei in one cell!

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…And they contain the

SAME genetic

information*SAME

NUMBER OF CHROMOSOME

S

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CytokinesisCytokinesis• Cytoplasmic divisionCytoplasmic division• Each cell gets half of the Each cell gets half of the

organelles.organelles.• After mitosis: cell pinches After mitosis: cell pinches

in half to form two new in half to form two new cells.cells.

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CytokinesiCytokinesiss•Animal cells Animal cells

pinch. pinch. •Cytokinesis in Cytokinesis in plant cells is plant cells is different from different from that in animal that in animal cells.cells.

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In plant cells a cell plate forms from the inside out.

•

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Mitosis review video clip with quiz!

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Results of Mitosis and Results of Mitosis and CytokinesisCytokinesis•Two new cells.

•The new cells- called daughter called daughter cells-cells- have the same number of chromosomes as the mother cell.

•This occurs in all somatic cells in your body.

•You have 46 chromosomes in all of your somatic cells-23 pair!

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Mitosis in Onion25

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Cells during Mitosis

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includes

is divided into

is divided into

Concept MapCell Cycle

M phase (Mitosis)Interphase

G1 phase

S phase

ProphaseG2 phase

Metaphase TelophaseAnaphase

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Reproduction of Sex Cells

•Sex cells- Sperm and egg•Process is called Meiosis•Similar to Mitosis

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MeiosisMeiosis•Cell divides twiceCell divides twice•First division is like First division is like mitosis and then the mitosis and then the cell divides again to cell divides again to create 4 haploid cells.create 4 haploid cells.

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MEIOSIS=CHROMOSOME REDUCTION DIVISION

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MeiosisMeiosis• Meiosis is also know as Meiosis is also know as

chromosome reduction division.chromosome reduction division.• Start with 46 and ends up with Start with 46 and ends up with

23.23.• Why?Why?• Fertilization creates the diploid Fertilization creates the diploid

condition againcondition againDiploiDiploidd

HaploidHaploid

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• Sperm formationSperm formation- 4 haploid sperm cells are formed.

• Egg formationEgg formation-most of the cytoplasm is used in one cell and the other three disintegrate. One haploid egg cell is formed.

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Meiosis Video ClipVideo Clip

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Crossing Over• Sometime

during meiosis the chromosomes can exchange information

• This is called Crossing Over

• Major source of genetic diversity in the species

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Prokaryotic CellsProkaryotic Cells

• Binary fission• Occurs in Prokaryotic

Cells• DNA is copied and

then the cell splits in half.

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Regulation of the Cell Cycle

• How do cells know when to divide? When to stop dividing?

• Cyclins-proteins that regulate the cell cycle.

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Cancer•Unregulated cell growth.

•Can form masses of cells called tumors.

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