Comparing Cell Cycles

Phase

Describe the events in each phase

G1   (1st growth stage)

This is also called the intermediate phase that occupies the time between the end of cell division in mitosis and the beginning of DNA replication.  At the G1 phase in order for the insurance of the appropriate conditions for support in DNA replication, the cell reviews the cellular environment and the cell size.

S (Synthesis)

At this phase the DNA are packaged into chromosomes is replicated in the cell cycle.  There are additional events that happen besides the replication of DNA such as, the cell growth, rate of synthesis of a number of proteins and enzymes which is involved with DNA synthesis.  When the cell contains twice its normal number of chromosomes is when the cell is ready to enter into Phase G2.

G2  (2nd growth stage)

This is the safety gap in which the cell checks over to make sure that eh entirely of its DNA  and other intertracllular components have been properly duplicated.  It also is the final chance for the cell to grow before it splits into 2 independent cells during mitosis.

Prophase of mitosis

Changes occur in the nucleus and the cytoplasm.  The chromatin fibers within the nucleus become more tightly coiled and folded in which forms discrete chromosomes.  With a narrow ‘waist” at the centromere, each duplicated chromosome appears as two identical sister chromatids joined together.  Where as in the cytoplasm, the mitotic spindle begins to form as microtubules rapidly grow out from the centrosomes (begin to move away from each other).  

Metaphase of mitosis

At this point the mitotic spindle is fully formed, where its poles are at the opposite ends of the cell.  An imaginary plane equidistant between the two poles of the spindle (metaphase plate).  On the metaphase plate, all the chromosomes centromeres are lined up.  The kintetochores of each chromosome of the 2 sister chromatids face opposite poles of the spindle.  At the chromatid the microtubules attach in which all come from one pole of the spindle,and those attached to its sister chromatid come from the opposite pole.

Anaphase of mitosis

This phase begins when two of the centromeres of each chromosome cones apart in which doing so separates the sister chromatids.  Each sister chromatid (once separated) is considered a full-fledged (daughter) Chromosome.  Toward opposite poles of the cell, along the microtubules the daughter chromosomes of the centromere-first walk in which this process is all powered by ATP.  When this is in progress the spindle microtubules attach to the kinetochores shorten.  The cell elongate when the poles move farther apart and the anaphase is over once the chromosomes have reached the two pole of the cell.

Telophase and ckytokinesis

In telophase, the start of the cell elongation in the anaphase continues.  The daughter nuclei appear at the two poles of the cell as nuclear envelopes form around the chromosomes.  Telophase is roughly the reverse of prophase in the terms of the chromosome and spindle structure.  The chromatin fiber of each chromosome uncoils and the mitotic spindle disappears in which this all happens by the end of the telophase.  The equal division of one nucleus into two genetically identical daughter nuclei is the now the finished outcome of mitosis.  

Cytokinesis: This happens along with telophase of the division of the cytoplasm of two daughter cells completely separating at the end of mitosis.  A cleavage furrow forms and the cells pinch into two, in which this happens in animal cells.  

Interphase

This phase is where the cell synthesizes new molecule and organelles. In the late interphase (G2), the cell will have doubled the contents and the cytoplasm contains two centrosomes.  Within the nucleus, the chromosomes are duplicated, but they are not distinguished individually yet because their form is loosely packed chromatin.