Late Interphase - During this period the nucleus is still well defined and bound by the nuclear envelope. It contains one or more nucleoli. Just outside the nucleus are the centrosomes which were
formed earlier by replication of a single chromosome. In animal cells, each centrosome features a pair of centrioles (brown stick like things inside the tan circle). Microtubules
extend from the centrioles. The chromosomes have already duplicated as the cell passed through S-Phase, but during this stage
they are still in the form of chromatin fibers.
Prophase - Changes occur in both the nucleus and the cytoplasm. The chromatin fibers inside the nucleus become more
tightly packed and will condense into discreet chromosomes. The nucleoli disappear and each duplicated chromosome now appears as two distinct
sister chromatids which are joined together. The cytoplasm changes includes the initial formation of the mitotic spindle. The centrosomes move away from each other
via microtubules.
Prometaphase - The nuclear envelope breaks into fragments and the microtubules of the mitotic spindle now interact
with the chromosomes, which have become very condensed. Each chromosome now has a kinetochore (black dot in the center that pinches the two sisters together)
Metaphase - Is characterized via the lining up of the sister chromatids at the Metaphase Plate. That is an imaginary line that runs through the middle of the cell.
The centromeres of all the chromosomes are aligned with each other and the microtubules attach to the kinetechores of each sister.
This entire apparatus of microtubules is called the "Spindle".
Anaphase - This stage begins when the paired centromeres of each chromosome separate which serves to liberate the sisters
from each other. They start to move towards the opposite poles of the cell as the microtubules shorten. At the same time
the poles are moving farther apart as well.
Telophase - The "cell" elongates even more and the nuclear envelope reforms to contain the DNA. The chromatin
will now become less tightly coilded. Cytokinesis (separation of the cytoplasm) is the last step and the cell forms a cleavage furrow (in animals cells only) and splits in two.
