1 How Cells Divide Chapter 12

2 Outline Cell Division in Prokaryotes Discovery of Chromosomes Structure of Chromosomes Phases of the Cell Cycle Interphase Mitosis Cytokinesis Cell Cycle Control Cancer

3 Cell Division in Prokaryotes Prokaryotic cell division occurs as ____________ in which cell divides into two halves. – Genetic information exists as a single, circular double-stranded DNA molecule.  Copying begins at replication origin, and proceeds bi-directionally.  One genome ends up in each daughter cell.

4 Binary Fission

5 Discovery of Chromosomes All ________________ cells store genetic information in chromosomes. – Most eukaryotes have between 10 and 50 chromosomes in their body cells.  Human cells have 46 ______________.  23 nearly-identical pairs

6 Structure of Chromosomes Chromosomes are composed of a complex of DNA and protein, ______________. – heterochromatin - not expressed – euchromatin - expressed DNA exists as a single, long, double-stranded fiber extending chromosome’s entire length. – forms __________ every 200 nucleotides  DNA coiled around _________ proteins

7 Eukaryotic Chromosomal Organization

8 Structure of Chromosomes ___________ - Individual’s particular array of chromosomes. – _________ - A cell possessing two copies of each chromosome (human body cells).  Homologous chromosomes are made up of sister chromatids joined at the _______________. – _________- A cell possessing a single copy of each chromosome (human sex cells).

9 Chromosomes

10 Phases of the Cell Cycle Five phases of cell division: – G 1 - primary growth phase – S - genome _________________ – G 2 - secondary growth phase  collectively called _____________ – M - mitosis – C - cytokinesis

11 Cell Cycle

12 Interphase G 1 - cells undergo majority of growth S - each chromosome __________ to produce sister chromatids – attached at centromere  contains attachment site (___________) G 2 - chromosomes condense – assemble machinery such as centrioles

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14 Mitosis Prophase – spindle apparatus assembled  _____________ connect kinetochores on each pair of sister chromatids to the spindle poles. – nuclear envelope breaks

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16 Mitosis Metaphase – chromosomes align in cell’s center  _____________plate  spindle

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18 Mitosis _________________ – sister chromatids pulled toward poles  poles move apart  centromeres move toward poles  ______________ shorten Telophase – spindle __________________ – nuclear envelope forms around each set of sister chromatids

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20 Cytokinesis Cleavage of cell into two halves – animal cells  constriction belt of actin filaments – plant cells  cell plate – fungi and protists  mitosis occurs within the nucleus

21 Cytokinesis

22 Cell Cycle Control Two irreversible points in cell cycle: – _____________ of genetic material – _____________ of sister chromatids Cell can be put on hold at specific ______________.

23 Cell Control Cycle G 1 / S - primary division ___________ point G 2 / M - _________________ to mitosis Spindle checkpoint - all chromosomes are attached to spindle

24 Growth Factors and the Cell Cycle Each growing cell binds minute amounts of positive ______________ (growth factors) that stimulate cell division. – If neighboring cells use up too much growth factor, there is not enough left to trigger cell division.  Growth factors trigger intercellular ________________ systems.

25 Cancer and Cell Proliferation Cancer is essentially a ______ of cell division ________ (unrestrained, uncontrolled cellular growth). – gene p53 plays a role in G 1 checkpoint  halts cell division if detects damaged DNA and stimulates activity of repair enzymes  appears to be __________ in many cancerous cells

26 Growth Factors and Cancer Growth factors influence cell cycle – ________________ - normal cellular genes that become oncogenes when mutated  positive approach that stimulates cell growth – _________________- negative approach that inhibits cell division

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28 Summary Cell Division in Prokaryotes Discovery of Chromosomes Structure of Chromosomes Phases of the Cell Cycle Interphase Mitosis Cytokinesis Cell Cycle Control Cancer

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