Mitosis “The Life and Times of the Cell”
Objectives List factors that influence when cells divide Understand & describe the ‘Cell Cycle’ Study the events of cell division (Mitosis) Compare Mitosis in plant & animal cells Cell Division Animation
Reading Assignment • Read Section 10-1, p.241-243 titled Cell Growth. • From the diagram indicating the Ratio of Surface area to Volume onp.243, sketch in your notes the smallest cell and the related statistics for Surface Area, Volume, and Surface Area to Volume Ratio and then sketch the largest cell with it’s related statistics. • Answer the 4 questions in 10-1 Section Assessment on p.243.
Cell Cycle – 4 Phases • Gap 1 (G1) • Typical cell growth & metabolism. • S Phase (S) • DNA Replication • Gap 2 (G2) • Centrioles Replicate • Protein synthesis • M Phase (M) • Mitosis phase / cell division occurs
Cell Cycle • The G1, S and G2 stages of the Cell Cycle happen during INTERPHASE. • The M phase consists of: Prophase; Metaphase; Anaphase; Telophase; Cytokinesis
S Phase - DNA Replication An enzyme called Helicase causes the hydrogen bonds that hold DNA together to break or ‘unzip’ Then DNA Polymerase allows free floating nucleotides to attach to the single strand of DNA DNA is Replicated
Draw DNA Replication • Draw a DNA triplet with the base sequence ATG on the left side. Make the 5’ the top left.
DNA Replication • Separate the original DNA strands. • With different colors, show the attachment of free-floating nucleotides.
DNA Replication • Where do the free-floating nucleotides come from? • Foods we eat! • How do the 2 strands compare? • They are exactly the same! • What happens if there is a mistake made during replication? • A mutation occurs!
Replication DNA Replication..Who wants to try? Replication Song
M Phase – Mitosis (4/5 Phases) • 1. Interphase • G1, S, & G2 phases • 2. Prophase • Early & Late • 3. Metaphase • 4. Anaphase • 5. Telophase • Early & Late • Cytokenesis
Early Prophase Replicated centrioles split and start moving to opposite sides of the cell forming ASTERS. Nuclear envelop disappears Replicated chromatin shortens, thickens and forms CHROMATID PAIRS
Late Prophase Centrioles have reached opposite poles of the cell SPINDLE forms Chromatid Pairs float throughout the cytoplasm.
Metaphase Shortest stage of Mitosis Chromatid pairs align at the equator of the spindle
Anaphase Chromatid pairs split Spindle fibers contract and the single CHROMOSOMES are pulled to opposite poles
Early Telophase Often described as the opposite of prophase Nuclear envelop reappears The chromosomes unravel to become chromatin Cleavage furrow begins to form
Late Telophase Cleavage furrow completes it’s indentation. “Mother” cell splits into 2 identical “Daughter” cells in a process called CYTOKINESIS
Summary of Mitosis Prophase: Replicated chromatin condense into chromatid pair Centrioles move to opposite poles Nuclear envelope disappears Spindle fibers start to form Metaphase Chromatid pairs line up at the equator Anaphase Chromatid pairs split Chromosomes are pulled to opposite poles by the spindle fibers Telophase Chromosomes de-condense into chromatin Nuclear envelope reappears Cytoplasm is divided into 2 cells Cytokinesis
Mitosis • I don't watch television when I can talk about Cell Division!
One more Phase – GAP 0 (G0) Some cells do not replicate their centrioles during Prophase. They lose their ability to divide They enter the Gap 0 stage Neurons of the Spinal cord / Brain cells
Mitosis in Plant vs. Animal CellsThe Rivalry Continues Plants have no centrioles but still form spindle fibers Plant cells divide from the inside out Cell Plate “Messy Metaphase”
Importance of Mitosis Method of reproduction for all single celled organisms Allows us to regenerate cells (tissue) repair cuts, bone breaks, etc Growth – one cell to trillions
How Long does the Cell Cycle Last? • Pick up a textbook and turn to page 249. • Read the section titled “Life Spans of Cells” and answer the 4 questions that follow.
Regulating the Cell Cycle • Turn in your textbook to page 250. Read pages 250 to 252. • Answer the 5 questions that follow. • Terms: Contact Inhibition; Cyclins; Internal regulators; External regulators; Cancer;