why do cells divide? genetically programmed cell volume gets too big external stimulus dividing...

Why do cells divide?

Genetically Programmed

Cell volume gets too big

External Stimulus

Dividing bacteria

Cell division = One cell makes two cells

Parent cell

DNA replicates

Two daughter cells are genetically

identical to each other and to parent

cell = clones

Chromatin = uncondensed DNA Chromosome = condensed DNA

The same DNA can appear in two forms

1 Chromosome 1 chromatid per chromosome

1 DNA double helix

1 Chromosome 2 chromatids per chromosome

2 DNA double helices

DNA replication

Cell division in eukaryotic cells:

Karyokinesis = division of the nucleus

Cytokinesis = division of the cytoplasm

Interphase 1. DNA called chromatin

2. DNA replicates

3. Cell does normal activities

4. Not a phase of mitosis

DNA = Chromatin

Interphase nucleus

Interphase

Chromatin in nucleus

Mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

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Prophase

Nuclear membrane disappears

Nucleolus disappears

Chromatin condenses into chromosomes

Spindle fibers appear

Chromatin

Chromosomes

MetaphaseChromosomes line up in center of cell

Chromatids (DNA double helix)

Two chromatids per

chromosome

Centromere = holds chromatids together

Anaphase =

Sister chromatids separate from each other

Telophase

Cytokinesis makes 2 new cells

Chromosomes decondense into chromatin

Nucleolus reappears

Nuclear membrane reappears

Early Telophase

Late Telophase

Animal cell membranes

pinches together

between two new cells

Plant cell wall grows

between two new cells

Cytokinesis

Plant Cytokinesis =

division of cytoplasm

Interphase

Telophase

AnaphaseMetaphase

Telophase

Telophase

ProphaseProphase

http://www.unm.edu/~asmund/mitosis.jpg

Interphase

Animal cytokinesis = pinching of plasma

membrane Late Telophase

Early telophase

Anaphase

Prophase Metaphase

http://images.google.com/imgres?imgurl=www.cll.wayne.edu/isp/mrichmon/Mitosis.gif&imgrefurl=http://www.cll.wayne.edu/isp/mrichmon/mitosis.htm&h=365&w=366&prev=/images%3Fq%3Dmitosis%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DN

Plant or Animal cell

mitosis?

Plant

Telomeres = break off and lead to cell death

and aging.Telomeres

Telomerase

Enzyme prevents loss of telomeres

Found in 95% of Cancer cells

Makes cells immortal

Cancer drug = telomerase inhibitor