Mitosis: The Great Divide

Why Would a Cell Divide? As cells absorb nutrients and get larger, a large demand is placed on the cell’s DNA & the volume of the cell increases faster than the surface area Surface area for exchange not great enough to support cell’s needs This means that a cell has difficulties with 1. absorbing enough nutrients 2. getting rid of waste fast enough So what’s a cell to do? divide in 2!

When Would a Cell Divide? Growth of the organism Repair of slightly damaged cells Replacement of cells Different cells divide at different rates: Most mammalian cells = 12-24 hours Some bacterial cells = 20-30 minutes

Getting Older… How does cell division change over a lifetime? All cells are only allowed to complete a certain number of divisions Then they experience apoptosis (programmed cell death or self destruction) How does cell division change over a lifetime? Childhood = cell division > cell death Adulthood = cell division = cell death The Later Years = cell division < cell death

The Cell Cycle vs Mitosis The Cell cycle includes all the steps required for an entire cell to divide (Interphase, Mitosis and Cytokinesis) Mitosis includes the steps that are carried out for only the nucleus to divide (Prophase, Metaphase, Anaphase and Telophase)

The Cell Cycle

Two Stages of the Cell Cycle 2 stages = Interphase-growth & replication of DNA & Mitotic phase (Mitosis & Cytokinesis)-division of cell into 2 daughter cells Cell spends about 90% of the time in interphase! Thanks to person who introduced me Explain presentation style Different, wacky, interactive Reason for madness- will be reviewed during implications May be asked to be an active participant May be asked to reinforce others Will be reinforced with candy Comments/questions welcomed throughout Reinforce me for doing well Have participants guess the number of new things they will learn today

Interphase G1 (1st gap) = cells absorb nutrients, grow & make proteins Divided into 3 phases: G1 (1st gap) = cells absorb nutrients, grow & make proteins S (synthesis) = cells duplicate DNA & continue to grow in preparation for cell division during mitosis G2 (2nd gap ) = cells keep growing & making proteins & get ready to divide in 2

Interphase occurs before mitosis begins What’s happening?? 1. Cells grow 2. DNA/Chromosomes are copied (DNA Replication!) Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase 3. Preparation for Mitosis CELL MEMBRANE Nucleus Cytoplasm

Interphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Mitosis Mitosis includes the steps that are carried out for only the nucleus to divide Mitosis is divided into 4 stages Prophase Metaphase Anaphase Telophase

Prophase 1st step in Mitosis Mitosis begins (cell begins to divide) Chromatin condenses and chromosomes become visible Sister chromatids held together by a centromere Nuclear membrane dissolves Centrioles appear and move to opposite end of the cell. Spindle fibers form between the centrioles. Centrioles Sister chromatids Spindle fibers

Prophase Plant Cell Animal Cell Spindle fibers Centrioles Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Metaphase 2nd step in Mitosis Chromosomes line-up along the center of the cell and attach to the spindle fibers at their centromere (center of chromosome) Centrioles Spindle fibers

Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Anaphase 3rd step in Mitosis Spindle fibers contract and sister chromatids (pairs of chromosomes) are pulled away from one another towards the poles or opposite ends of the cell. Centrioles Spindle fibers

Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Telophase 4th and final step in Mitosis Nuclear membranes form around the two new nuclei . Chromosomes appear as chromatin (threads rather than rods). Mitosis ends. Nuclear membranes Nucleus Nucleus Chromatin

Telophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

Cytokinesis occurs after mitosis Cell membrane moves inward to create two identical daughter cells – each with its own nucleus containing identical chromosomes. The cytoplasm is distributed equally between the two new cells before separation

What Mitosis Actually Looks Like Interphase Metaphase Prophase Telophase Anaphase http://www.sci.sdsu.edu/multimedia/mitosis/mitosis_gif2.html http://science.nhmccd.edu/biol/bio1int.htm

Animal Mitosis Interphase                                                              Prophase                                                              Metaphase                                                              Anaphase                                                              Telophase                                                             

Plant Mitosis Interphase                                                              Prophase                                                              Metaphase                                                              Anaphase                                                              Telophase                                                             

Summary of Mitosis

What Happens After Mitosis? The cells return to interphase Chromosomes uncoil back into chromatin The cycle repeats itself over & over…

Mitosis Animation http://www.cellsalive.com/mitosis.htm

Can You Identify the Stages of Mitosis? Put the following mitosis stages in the correct sequence