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 Cell Division Animation

Reading Assignment Read Section 10-1, p 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 Cell Cycle – 4 Phases Cell Cycle 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? DNA Replication..Who wants to try? Replication Song Replication Song

M Phase – Mitosis (4/5 Phases) Mitosis 1. Interphase –G1, S, & G2 phases 2. Prophase –Early & Late 3. Metaphase 4. Anaphase 5. Telophase –Early & Late Cytokenesis

Interphase

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

Remember this Diagram?

Early Prophase

Late Prophase Centrioles have reached opposite poles of the cell SPINDLE forms Chromatid Pairs float throughout the cytoplasm.

Late Prophase

Metaphase Shortest stage of Mitosis Chromatid pairs align at the equator of the spindle

Metaphase

Anaphase Chromatid pairs split Spindle fibers contract and the single CHROMOSOMES are pulled to opposite poles

Anaphase

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

Early/Late Telophase

Summary of Mitosis 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 Cytokenesis

Mitosis I don't watch television when I can talk about Cell Division! 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 Cells The Rivalry Continues Plants have no centrioles but still form spindle fibers Plant cells divide from the inside out Cell Plate “Messy Metaphase”

Plant Cell Mitosis

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. 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;

Meiosis Special cell division that produces Haploid sex cells Consists of one replication and two cell divisions

Sexual vs. Asexual Asexual Reproduction Reproduction that doesn't involve sex cells Produces ‘clones’ of previous cells Ex: 1. Binary Fission 2. Fragmentation 2. Fragmentation 3. Budding 3. Budding Sexual Reproduction Reproduction involving sex cells Produces genetically different offspring Sperm + egg = Zygote (n) + (n) = (2n) (n) + (n) = (2n)

Cancer A disease of uncontrolled cell division Starts with a single cell that loses its control mechanisms due to a genetic mutation (mistakes in DNA replication) Can be caused naturally or by carcinogens (i.e.: tobacco smoke, chemicals, etc.) That cell starts dividing without limit, possibly killing the host (without treatment)

Cancer Treatment Three basic treatments: –Surgery to remove cancer –Radiation to kill affected cells –New drugs are becoming available (Chemotherapy) It is hard to remove cancer (tumors often lack clear boundaries) –Some tumors are very small and are found throughout the body (advanced stages) Radiation and chemotherapy are aimed at killing cancer cells –The body then has to replace those dead cells which requires a lot of energy –Therefore treatment must be balanced with overall patient health Unfortunately due to natural selection cancer that seems to have disappeared can come back in the future in a form that is resistant to the radiation / chemotherapy Using multiple drugs can decrease the risk of relapse –Multiple drugs decrease the probability of cells acquiring immunity