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Cellular Reproduction Chapter 9

9.1: Cellular Growth MAIN IDEA: Cells grow until they reach their size limit, then they either stop growing or divide.

Cell Size DON’T COPY  Most cells – only 100 micrometers in diameter  Why are they so small???  Do large or small cells perform tasks more efficiently?

Surface Area : Volume DON’T COPY  This ratio is extremely important to cells  To calculate for a cube: Surface area = ? Volume = ?

Surface Area : Volume DON’T COPY  Surface Area of cube = L x W x 6  Volume = L x W x H

Calculate SA:V ratio

Surface Area : Volume DON’T COPY  What happened to the ratio when the cells became larger?

Surface Area : Volume DON’T COPY  As cell grows, volume increases faster than surface area, so this ratio becomes smaller  LARGER ratio (smaller cells) – more beneficial to cells  Cell needs large surface area to get enough nutrients and expel wastes efficiently

Cell’s Life Cycle  Cells grow only so big; too big makes cell inefficient  If cell reaches size limit it: Stops growing OR Divides  When cells divide, they make an exact duplicate of themselves.  Result = 2 identical cells

Eukaryotes’ Cell Cycle  Cycle of cells growing and dividing  After 1 complete cycle, 1 cell becomes 2 cells  3 main parts: Interphase Division (Mitosis) Cytokinesis

Interphase  Cell spends most of its life in interphase  Called “resting” phase, but cell is chemically active Metabolism (chemical reactions) Preparation for division

3 Parts of Interphase

Interphase  G1: Cell grows, active metabolism, organelles duplicated  S: DNA replicated  G2: Has twice as much DNA as G1 phase cell, prepares for mitosis, triggers division and ends interphase

Mitosis (M) Phase  Mitosis – nucleus and nuclear material divide  Chromosomes can be seen under microscope  Divided into 4 sub-stages

Chromatin

Chromosomes

Cytokinesis  Cytokinesis - when cytoplasm divides

9.2: Mitosis and Cytokinesis MAIN IDEA: Eukaryotic cells reproduce by mitosis, the process of nuclear division, and cytokinesis, the process of cytoplasm division.

Mitosis  Nuclear division  Continuous process  Seen in stages  Result = 2 genetically identical daughter cells

Stages of Mitosis 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Prophase  Pro = first  Chromatin coils, shortens, and thickens into chromosomes  Nuclear membrane starts to disappear

Prophase  Spindle fibers (microtubules) form in cytoskeleton, and chromosomes’ centromeres attach to fibers  Spindle apparatus = all microtubule fibers and centrioles (in animal cells)

Prophase

Metaphase  Meta = change  Pairs of chromosomes move to center of cell, along equator, perpendicular to spindle fibers

Anaphase  Ana = up  Chromatids separate, each pair moving to opposite ends of cell along spindle fibers

Telophase  Telo = end  Chromosomes reach opposite ends of the cells; new nuclear membrane starts forming to make 2 identical nuclei

Cytokinesis  Cytoplasm divides in half, duplicated organelles move apart

Plant and Animal Cells  Similar process of mitosis, but some differences  Animal cells have 2 centrioles  Plant cells form a cell plate during cytokinesis (preliminary cell wall); animal cells pinch across middle instead to separate

Prokaryotes  Binary fission  Chromosome replicates  Cell elongates  Membrane/wall forms in middle, dividing cell

Name the phase

9.3: Cell Cycle Regulation MAIN IDEA: The normal cell cycle is regulated by cyclin proteins.

Normal Cell Cycle  Timing and rate of cell cycle controlled by 2 substances: Cyclins – proteins Cyclin-dependent kinases (CDKs) – enzymes that bind to cyclin  Different combinations signal different activities during the cell cycle

Activities Controlled by CDK/Cyclin:  Start of cell cycle  DNA replication  Protein synthesis  Nuclear division (mitosis)  End of cell cycle

Abnormal Cell Cycle: Cancer  Cells divide repeatedly and uncontrollably  No ability to stop the progression of division at checkpoints (which allow normal cells to stop dividing if something goes wrong)  Cancer cells overcrowd normal cells, stopping their normal function and killing the organism

Causes of Cancer  Changes/mutations in DNA affect proteins that control cell cycle  Carcinogens – substances or agents that cause cancer

What are Some Common Carcinogens?

 Tobacco  Exposure to x-ray radiation  Exposure to UV radiation (from Sun)  Air pollution  Alcohol  Food with many preservatives

Genetics  Higher risk of mutations over time – so more likely for older people to develop cancer  Can run in families

Apoptosis  Programmed cell death  Occurs in development – webbing between fingers/toes  Occurs in plants losing leaves  Prevents damaged cells from dividing  Prevents cancer

Stem Cells  Unspecialized cells – specialize under right conditions  Embryonic – result shortly after fertilization; cells eventually specialize into tissues (controversial research)  Adult – always found in some tissues  Can be used to treat certain diseases/conditions