Cell Division 1.6

Essential Idea: Cell division is essential but must be controlled. 1.6 Cell Division Understandings: Mitosis is division of the nucleus into two genetically identical daughter nuclei   Chromosomes condense by supercoiling during mitosis Cytokinesis occurs after mitosis and is different in plant and animal cells Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm Cyclins are involved in the control of the cell cycle Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumors Application: The correlation between smoking and incidence of cancers Skills: Identify the phases of mitosis Determine the mitotic index from a micrograph

Interphase G1 – growth, normal cell functions (protein synthesis, cellular respiration, metabolism, etc.) S – DNA Replication C. G2 – normal cell functions, growth, and prep for division (organelles increase in number, DNA begins to condense from chromatin to chromosomes, microtubules may begin to form)

II. Checkpoints – cell cycle pauses until allowed to proceed 1 II. Checkpoints – cell cycle pauses until allowed to proceed 1. Cyclins – proteins that control the cells progression through the cell cycle a. Bind to cyclin-dependent kinases (CDKs) which enable the cyclins to act as enzymes

III. Mitosis – Nuclear division (Actually a continuum but we describe as distinct phases)

Prophase 1. Chromosomes condense – supercoiling tightly around histones 2. Nucleolus breaks down 3. Microtubules grow from microtubule organizing centers (MTOCs)

5. Centrosomes move toward opposite poles 4. Nuclear envelope breaks down 5. Centrosomes move toward opposite poles 6. Spindle fibers attach to kinetochore at centromeres

Metaphase 1. Centrosomes reach opposite poles 2. Spindle microtubules pull on chromosomes causing them to line up single-file on the metaphase plate (equator of cell)

Anaphase – (shortest phase) 1. Cell elongates due to pushing and pulling of microtubules 2. Microtubules shorten, pulling sister chromatids apart

Chromatids move to opposite poles – centromeres 1st At end of anaphase, each pole has a complete, identical set of chromosomes

Telophase 1. Nuclear membrane starts to re-form 2. Chromosomes de-condense 3. Nucleolus reappears 4. Spindle apparatus disintegrates

IV. Cytokinesis A. Animal cells – pinches inward forming a cleavage furrow B. Plant cells – cell plate forms in middle

V. Cancer A. Cell cycle is out of control B V. Cancer A. Cell cycle is out of control B. Results in a mass of abnormal cells (tumor) 1. Primary tumor – original location 2. Secondary = metastasis – spreads to other location(s)

Oncogenes – mutations in these genes contribute to normal cells becoming cancerous Can be triggered by outside agents Sun, chemicals, smoke