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Why do cells divide?

• Growth and Repair• Creation of gametes

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Chromosomes

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Made of densely packed DNA

Human Eukaryotic Cells

1.Somatic (body) cells

A.46 chromosomes

b.Diploid2.Sex cells (gametes)

a.23 chromosomes

b.Haploid

Why would sex cells need half the number of chromosomes ?

Karyotype

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Homologous Chromosomes--Chromosome pairs that carry genes for the SAME trait

An organized profile of persons chromosomes

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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 (replication)

• G2 phase- Gap phase. Preparation for Mitosis. Organelles are produced.

Interphase

Body Cells

Sex cells are

called gamete

s

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MitosisMitosis• Nuclear Division.• Nucleus divides once into two

identical nuclei with the same DNA • YEILD: 2 diploid somatic cells

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MeiosisMeiosis• Nuclear Division.• Nucleus divides twice into four

=nuclei with different DNA • YEILD: 4 haploid gametes

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Mitosis Meiosis

1.Which type of cells go through Mitosis?

5.Which type of cells go through Meiosis?

2.The nucleus divides into how many nuclei?

6.How many times does the nucleus divide?

3.Is the DNA the same or different?

7.Is the DNA the same or different?

4.What does mitosis yield ( or make) ?

8.What does meiosis yield ( or make)?

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Mitosis Meiosis

1.Which type of cells go through Mitosis?Somatic ( Body)

5.Which type of cells go through Meiosis?Gametes (Sex)

2.The nucleus divides into how many nuclei?2

6.How many times does the nucleus divide?2

3.Is the DNA the same or different?same

7.Is the DNA the same or different?different

4.What does mitosis yield ( or make) ?2 identical diploid somatic cells

8.What does meiosis yield ( or make)?4 different haploid gametes12

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4 Steps of Mitosis (PMAT)•  Prophase:

• Chromosomes condense

• Nuclear membrane breaks down.

• Centrioles move to opposite sides of the cells

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14 Metaphase:Metaphase: -Chromosomes attach to

spindle fibers-Chromosomes line up

in the middle of the cell

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

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Telophase There are now TWO nuclei in one cell!

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…And they contain the

SAME genetic

information*SAME

NUMBER OF CHROMOSOME

S

• Nuclear Envelope reforms

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CytokinesisCytokinesis• Cytoplasmic Cytoplasmic

divisiondivision• Each cell gets half Each cell gets half

of the organelles.of the organelles.• cell pinches in half cell pinches in half

to form two new to form two new cells.cells.

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

•

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Mitosis in Onion25

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includes

is divided into

is divided into

Concept Map

Cell Cycle

M phase (Mitosis)

Interphase

G1 phase

S phase

ProphaseG2 phase

Metaphase TelophaseAnaphase

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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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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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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 PhasePhase

Organelles must be Organelles must be replicated (copied)replicated (copied)

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M PhaseM PhaseTwo parts:Two parts:

1.1.Nuclear divisionNuclear division– MitosisMitosis

2.2.Cytoplasmic Cytoplasmic DivisionDivision– CytokinesisCytokinesis 10

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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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Cells during Mitosis

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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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