The Basics of Mitosis aka Asexual Reproduction Important as a GUTS lecture for two reasons: Although you’ve had it before, probably introduced as far back as middle school, it’s easy to forget and to understand it only in the broadest terms. I’ve found that typically we don’t understand (especially meiosis) until we sit down and draw out what happens to the chromosomes. it’s of extraordinary importance. The mechanisms of inheritance and the patters we see in the heritibility of human disease and characteristics depend at their base on how meiosis works. Likewise, major diseases like cancer, hinge on aspects of mitosis.

What is Mitosis? IOW: Single Parent cell divides to produce two Somatic cell (body cell) division consisting of nuclear division & cytoplasmic division (cytokinesis) IOW: Single Parent cell divides to produce two identical daughter cells a.k.a. Asexual Cell Reproduction Called asexual because no combination of cellular material occurs – all new cells produced contain the same genetic material as the original cell.

“You cannot step twice into the same river”…Heraclitus of Ephesus, c “You cannot step twice into the same river”…Heraclitus of Ephesus, c.535 -475 BCE You literally are not the same person you were in the past Cell division is required for Growth & Development Human zygote = 1 cell Mature adult = 1 X 1014 cells We wear out Cell division is the primary manner in which we deal with the harmful effects of wear and damaging forces in our environment Stem cells form a pool of self-renewing cells as “replacement parts”

What do all cells require to survive? A complete set of Genetic Material or instructions in order to produce required molecules direct life processes We need an orderly process to duplicate and distribute chromosomes through successive cell divisions

Genetic Material The genetic material in a cell is DNA (deoxyribonucleic acid) It is found in a different form depending on the stage of the cell cycle Chromatin – long, thin threadlike material - present in this state during interphase Chromosomes – small, sausage-like, may be found as a individual chromatids (late stages of cell division) or as paired chromatids (sisters) connected at the centromere.

All somatic cells contain homologous pairs of chromosomes - one from the mother’s egg (maternal chromosome) and one from the father’s sperm (paternal chromosome) – in the human, 23 sets (46 chromosomes total) Each homologous pair is similar in shape and length and is responsible for the same types of characteristics Sister chromatids are IDENTICAL to each other (exact copies)

Gene Chromosome DNA Gene = a segment of DNA that codes for a protein Genes  You Chromosome = consists of DNA tightly coiled around proteins

Diploid organisms receive one chromosome from their female parent (maternal chromosome) and one chromosome from male parent (paternal chromosome) A “matched” pair of maternal and paternal chromosomes are called homologues Humans - 23 pairs of homologous chromosomes 22 pairs of autosomes and 1 pair of sex chromosomes

Why pairs? Diploid = 2n Mom Dad Pair 1-22 = Autosomes Pair 23 = Sex Gene   Gene Gene   Gene Pair 1-22 = Autosomes Gene   Gene Gene   Gene Pair 23 = Sex Chromosomes

Cell Cycle: Interphase: No Division G1: 10-12 hrs-cell grows in size & organelles replicated S: 6-8 hrs-replication of DNA, synthesis of proteins associated with DNA G2: 2-4 hrs-synthesis of proteins associated with mitosis (Centrioles stretch their legs!)

Interphase (up to 90% of the cell cycle) – divided into three separate phases G1 phase – (growth 1) – general growth & organelle replication, DNA consists of a single (unreplicated) chromatin molecule (46 strands) S phase – (synthesis) – replication of chromosomal material (DNA)  2 copies of each chromosome (23 pairs in humans), can be identified by the uptake of a radioactive base G2 phase (growth 2) – structures associated with mitosis & cytokinesis are replicated (cell membrane proteins, centrioles)

The Phases of Mitosis 4 phases: 1st – Prophase 2nd – Metaphase 3rd – Anaphase 4th – Telophase/Cytokinesis

92 PMAT 46 46 Cytokinesis 46 46

Prophase Centrioles duplicated to form two pairs chromatin nucleus centrioles nucleolus Centrioles duplicated to form two pairs Chromosomes begin to condense

Prophase condensing chromosomes Nuclear envelope begins to break down Spindle fibers form (specialized microtubules) Radiate out from centrioles forming the “aster” One pair of centrioles migrates to one pole of cell, the other pair migrates to opposite pole of cell

The Mitotic Spindle Spindle fibers are specialized microtubules Spindle fibers radiate out from centrioles forming the “aster” Centrioles occur in pairs, and are duplicated during Prophase

Duplicated chromosome Prophase The Spindle Captures Chromosomes When spindle fibers are fully formed, nuclear envelope disintegrates & nucleolus disappears Spindle fibers attach to chromosomes at the kinetochore, a structure located at the centromere Duplicated chromosome (2 sister chromatids)

Prophase Function of spindle fibers is to organize division of sister chromatids into daughter cells Other spindle fibers do NOT attach to chromosomes, but retain free ends that overlap at cell’s equator > “free spindle fibers”

Metaphase Chromosomes align along equator of the cell, with one kinetochore facing each pole centrioles chromosomes spindle fibers

Anaphase Sister chromatids separate Spindle fibers attached to kinetochores shorten and pull chromatids poleward free spindle fibers lengthen and push poles of cell apart The same number of single-copy chromosomes should be at each pole

Telophase Chromosomes decondense into Chromatin spindle fibers disintegrate pinching of cell membrane at equator nuclear envelope reforms nucleolus reappears

Animal Cell: ring contracts, dividing the cytoplasm microfilaments attach to plasma membrane to form a ring around equator of cell (cleavage furrow) cytokinesis Animal Cell: ring contracts, like a drawstring, dividing the cytoplasm Plant cells, a cell-plate forms first, separating the two cells by the forming cell wall Daughter Cells

CYTOKINESIS Animal Plant “Cleavage Furrow” “Cell Plate”

3 1 Prophase Anaphase 4 Which? Telophase 2 Metaphase 5 Interphase

Control of the Cell Cycle 90% time in Interphase Feedback signals – “red/green light” Controlled by proteins

Cancer = uncontrolled growth/division of cells If gene that contains info for cell growth/division is mutated = Cell growth/division unregulated

Tumor “benign tumor” “malignant tumor” Metastasis- Therapy?- = a mass of abnormal cells. “benign tumor” “malignant tumor” Metastasis- Start more tumors Therapy?- Radiation therapy Chemotherapy with toxic drugs. Mammograms 

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