Ap Bio Ch. 12

Front 1

G2 Phase of Interphase

Back 1

-A nuclear envelope bounds the nucleus.
-The nucleus contains one or more nucleoli.
-Two centrosomes have formed by replication of a singly centrosome.
-In animal cells each centrosome features two centrioles.
-Chromosomes, duplicated during S phase, cannot be seen individually because they have not yet condensed.

Front 2

Prophase

Back 2

-The chromatin fibers become more tightly coiled, condensing into discrete chromosomes observable with a light microscope.
-The nucleoli disappear.
-Each duplicated chromosome appears at 2 identical sister chromatids joined together.
-The mitotic spindle begins to form. It is composed of the centrosomes and the microtubules that extend from them. The radial arrays of shorter microtubules that extend from the centrosomes are called asters.
-The centrosomes move away fro m each other, apparently propelled by the lengthening microtubules between them.

Front 3

Prometaphase

Back 3

-The nuclear envelope fragments.
-The microtubules of the spindle can now invade the nuclear area and interact with the chromosomes which have become more condensed.
-Microtubules extend from each centrosome toward the middle of the cell.
-Each of the 2 chromatids of a chromosome now has a kinetochore, a specialized protein structure located at the centromere.
-Some of the microtubules attach to the kinetochores, becoming kinetochore microtubules. These jerk the chromosomes back and forth.
-Nonkinetochore microtubules interact with those from the opposite pole of the spindle.

Front 4

Metaphase

Back 4

-The longest stage of mitosis lasting about 20 minutes.
-The centrosomes are now at opposite ends of the cell.
-The chromsomes convene on the metaphase plate, an imaginary plane that is equidistant between the spindles two poles. The chromosome's centromeres lie on the metaphase plate.
-The kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles.
-The entire apparatus of microtubules is called the spindle because of its shape.

Front 5

Anaphase

Back 5

-Shortest stage of mitosis.
-Begins when the 2 sister chromatids of each pair suddenly part. Each chromatid thus becomes a full fledged chromosome.
-Two liberated chromosomes begin moving toward opposite ends of the cell, as their kinetochore shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere first.
-The cell elongates as the nonkinetochore microtubules lengthen.
-The two ends of the cell have equivalent and complete collections of chromosomes.

Front 6

Telophase

Back 6

-2 daughter nuclei begin to from in the cell.
-Nuclear envelopes arise from the fragments of the parent cell's nuclear envelope and other portions of the endomembrane system.
-The chromosomes become less condensed.
-Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.

Front 7

Cytokinesis

Back 7

-The division of the cytoplasm is usually well underway by late telophase, so the 2 daughter cells appear shortly after the end of mitosis.
-In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.