Cell Cycle and Mitosis

Cell Cycle Only a Eukaryotic Process Rate may differ depending upon: Unicellular: asexual reproduction Multicellular: growth and repair Rate may differ depending upon: Type of cell Age of cell External factors that affect cells Genetics

Type of Cell The function of the cell, type of tissue often determine the rate of it’s cell cycle Fastest include: intestinal, skin, bone marrow, hair Slowest: bone, liver, kidney

Age of Cell/Organism In multicelled organisms the rate of the cell cycle can also depend upon the number of times the cell has divided, ie ‘age’ “Age” is a factor of cell division vs cell death Young: cell division > cell death = growth Middle: cell division = cell death Old: cell division< cell death

Why can’t organisms live forever? Cells cannot grow and divide indefinitely. At the end of chromosomes are small ‘caps’ called telomeres that help keep the DNA from uncoiling. Every time the DNA is replicated a piece of the telomere is lost. When the telomere is gone the DNA can no longer replicate and the cell dies. Interestingly, telomeres are found in the cells of multicelled organisms, but, not unicellular…what would happen if there were?

External Factors Factors outside of the cell or organism can affect the cell cycle. Cells are exposed to many environmental factors that can directly influence the control and regulation of a cell’s cycle Examples include: Drugs, Alcohol, Smoke, Radiation, Toxins, Viruses All of these carcinogens disrupt the cell cycle and can cause cells to divide uncontrollably forming the tumors associated with many cancers

Genetic Factors Some mutations to genes can result in changes to the cell cycle. The BRCA1 gene can cause breast cancer Progeria is a genetic disorder marked by rapid aging

The Cell Cycle Occurs in 3 phases Interphase: preparation for division Mitosis: nuclear division Cytokinesis: cell division BATMAN

Mitosis Prophase Metaphase Anaphase Telophase M C NERVE/MUSCLE

INTERPHASE Use to be referred to as the cell’s ‘resting phase’, however, actually a lot of activity is occurring during this time. Approximately 80% of cell’ life is spent in interphase Marked by 3 distinct stages: Gap 1 (G1 ) follows cytokinesis, time of cell growth, replication of organelles (1st Checkpoint) Synthesis(S) Replication of DNA in preparation for division Gap 2: (G2 )growth slows, cell enzymes check DNA (2nd Checkpoint)

MITOSIS M Phase: Process that divides the nucleus containing the replicated DNA Approximately 15% of cell’s life cycle 4 Stages PROPHASE: “before”; replicated DNA uncoils METAPHASE: “after”; chromosomes align (3rd Checkpoint) ANAPHASE: “opposite”; chromosomes separate TELOPHASE: “across”; chromosomes recoil

CYTOKINESIS Division of the cell Means “to move the cell” Approximately 5% of cell’s life Process differs in Heterotrophs(Animals) Autotrophs(Plants) due to presence of cell wall HETEROTROPHS AUTOTROPHS Cell membrane indents at cleavage furrow and cell is ‘pinched’ in half The cell divides from the center with the formation of cell plate(cellulose) and cell is ‘cut’ in half

CUT YOUR PIECES OUT QUICKLY NO NEED TO CUT CLOSE TO EDGE, JUST DON’T CUT OFF LABEL LINES OR BRACKETS

GROUP THEM AS AUTOTROPHIC AND HETEROTROPHIC

ON YOUR DESK… ARRANGE THE DIAGRAMS FOLLOWING THE 4 STEPS OF MITOSIS(PMAT) MAKE SURE TO KEEP THE CHROMOSOMES IN THE SAME ORIENTATION: EAST-WEST THEN WHEN YOU ARE SURE YOU ARE CORRECT… GLUE THEM INTO THE CORRESPONDING BOXES ON THE WORKSHEET

Cell Cycle : Let’s Review Checkpoint 3 Are chromosomes aligned? cytokinesis Checkpoint 2: Has DNA replicated correctly? Checkpoint 1: Have organelles copied? Is cell large enough to divide?

G0 Arresting phase where certain cells leave the cell cycle and stop dividing Some cells, once formed, remain in G0 for the life of the organism. These cells cannot be replaced once damaged. Examples: Nerve and Muscle Some cells enter an extended period of G0 , however, can be replaced overtime. Examples: Liver and Kidney

Steps of Mitosis

PROPHASE Heterotroph/Animal Autotroph/Plant Centrosome duplicates and move to opposite poles Centrioles, in centrosome , form the mitotic spindle Duplicated chromosomes, called chromatids, are held together by centromere Nuclear membrane and nucleolus begin to breakdown Heterotroph/Animal Autotroph/Plant NO CENTRIOLES in PLANT CELLS centrioles centrosome sister chromatids centromere

METAPHASE Heterotroph/Animal Autotroph/Plant Spindle fibers attach to centromere and maneuver sister chromatids to central plane of the cell Heterotroph/Animal Autotroph/Plant Mitotic Spindle Kineticore fibers Polar fibers

ANAPHASE Heterotroph/Animal Autotroph/Plant Spindle fibers are drawn into the centriole pulling apart the two sister chromatids. At this point they are referred to as chromosomes again. Heterotroph/Animal Autotroph/Plant   No Centriole in Plant

TELOPHASE Heterotroph/Animal Autotroph/Plant Nuclear envelope and nucleolus reform around chromosomes Mitotic spindle breaks down Cytokinesis begins Heterotroph/Animal Autotroph/Plant Cleavage furrow forms cell is pinched in half Cell plate forms from center and cell is cut in half