MITOSIS The Cell Cycle & Mitosis Tutorial

INTERPHASE The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules.

PROPHASE Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.

Prophase The nuclear membrane dissolves, marking the beginning of prometaphase. Proteins attach to the centromeres creating the kinetochores. Microtubules attach at the kinetochores and the chromosomes begin moving.

METAPHASE Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.

ANAPHASE The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.

TELOPHASE Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage.

CYTOKINESIS In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus. In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells.

MITOSIS NOTES ? WHAT DO YOU THINK WOULD HAPPEN IF A CELL WERE SIMPLY TO SPLIT INTO TWO, WITHOUT ANY ADVANCE PREPARATION? WOULD EACH DAUGHTER CELL HAVE EVERYTHING IT NEEDED TO SURVIVE? NO CHROMOSOMES –FRUITFLIES – 8 Pairs CHROMOSOMES –HUMANS – 23 Pairs CHROMOSOMES –CARROT CELLS – 18 Pairs CHROMOSOMES CHROMATIDS – ONE OF TWO IDENTICAL “SISTER” PARTS OF A DUPLICATED CHROMOSOME CENTROMERE – LOCATED NEAR THE MIDDLE OF THE CHROMATIDS, SOME LIE NEAR THE END ?WHEN ARE CHROMOSOMES VISIBLE? * DURING CELL DIVISION ? WHY ARE THE SISTER CHROMATIDS IDENTICAL? * BEFORE CELL DIVISION EACH CHROMOSOME IS DUPLICATED. THE SISTER CHROMATIDS THEREFORE ARE IDENTICAL BECAUSE THEY ARE DUPLICATES OF EACH OTHER

THE CELL CYCLE –INTERPHASE – PERIOD OF THE CELL CYCLE BETWEEN CELL DIVISION G1 – Cell does what it is supposed to do S – Synthesis of DNA G2 – Cell grows and prepares for the cell to split or cell division –Growth –Reproduction of cell material, organelles

–CELL CYCLE – THE PERIOD OF TIME FROM THE BEGINNING OF ONE CELL DIVISION TO THE BEGINNING OF THE NEXT –DURING THE CELL CYCLE, A CELL GROWS, PAREPARES FOR DIVISION, AND DIVIDES TO FORM 2 DAUGHTER CELLS, EACH OF WHICH THEN BEGINS THE CYCLE AGAIN. FIGURE 10-4 PG. 245 OR WORKSHEET CH. 10 CELL GROWTH AND DIVISION –MITOSIS – M PHASE – THE DIVISION OF THE CELL NUCLEUS AND CYTOKINESIS TAKES PLACE S – COPY OF CHROMOSOMES

EVENTS OF THE CELL CYCLE INTERPHASE IS LONG, THE ACTUAL CELL DIVISION TAKES PLACE QUICKLY

MITOSIS –BIOLOGISTS DIVIDE THE EVENTS INTO 4 PHASES: PROPHASE, METAPHASE, ANAPHASE, TELOPHASE CAN LAST FOR A FEW MINUTES OR UP TO SEVERAL DAYS –PROPHASE 1ST, LONGEST PHASE 50-60% CHROMOSOMES BECOME VISIBLE CENTRIOLES – FORM SPINDLE, SEPARATE AND TAKE UP POSITIONS ON OPPOSITE SIDES OF THE NUCLEUS NUCLEOLUS DISAPPEARS AND NUCLEAR ENVELOPE BREAKS DOWN

PROPHASE Draw this in your notes

EARLY PROPHASE

LATE PROPHASE

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METAPHASE CHROMOSOMES LINE UP ACROSS THE CENTER OF THE CELL

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ANAPHASE CENTROMERES THAT JOIN THE SISTER CHROMATIDS SPLITS, CAUSING THE SISTER CHROMATIDS TO SEPARATE AND BECOME INDIVIDUAL CHROMOSOMES. THEY MOVE TO THE POLES. ANAPHASE STOPS WHEN THE CHROMOSOMES STOP MOVING.

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TELOPHASE CHROMOSOMES UNCOIL NUCLEAR ENVELOPE REAPPEARS AROUND CLUSTER OF CHROMOSOMES. SPINDLE BEAKS APART. NUCELOLUS REAPPEARS

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CYTOKINESIS USUALLY OCCURS THE SAME TIME TELOPHASE HAPPENS ANIMAL – PINCHED INTO NEARLY 2 EQUAL PARTS PLANT – CELL PLATE GRADUALLY DEVELOPS INTO A SEPARATING MEMBRANE

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DAUGHTER CELLS

ONION ROOT

Mitosis in Onion Root Tips