The Cell cycle

What is the Cell Cycle:
The cell cycle is an ordered set of events which lead to cell growth and division into two daughter cells. Non-dividing cells are not considered to be in the cell cycle. The stages are G1-S-G2-M. The G1 stage stands for "GAP 1". The S stage stands for "Synthesis". This is the stage when DNA replication occurs. The G2 stage stands for "GAP 2". The M stage stands for "mitosis", and is when nuclear (chromosomes separate) and cytoplasmic (cytokinesis) division occur.  22-Cell-cycle.gif

Phases of Interphase (G1-S-G2)
  1. The G1 (gap 1) stage is when the cell is prepared for division. All cellular components but the chromosomes are duplicated, the cell increases in size, and mRNA and proteins are synthesized. At a certain point - the restriction point - the cell is "committed" to division and moves into the S phase.
  2. The S (synthesis) stage is when the DNA within the cell is replicated. Each of the 46 chromosomes split into two sister chromatids (threadlike strands, each one half of a chromosome) to form the iconic X shape. While the chromosomes have duplicated, there are still 46 chromosomes within the cell, as 2 sister chromatids joined by one centromere is still considered a chromosome, just a duplicated one. Each chromosome is duplicated by the cell to prepare for total cell division.
  3. The G2 (gap 2) stage is when the cytoplasmic materials needed for mitosis and cytokinesis are created. Most microtubules are created during this phase. The cell also makes sure that all the chromatids have no errors, and if they does it makes repairs.Image result for interphase
Phases of Mitosis:
  1. Prophase - Chromatin, the material that composes chromosomes, begins to condense and becomes visible in light microscopes. The nucleolus disappears. Centrioles begin moving to the other side of a cell and fibers extend from the centromeres (the point on a chromosome which connects the two chromatids), while fibers cross the cell to form the mitotic spindle (used to position chromosomes within the cell).Image result for prophase
  2. Metaphase - Spindle fibers (microtubules) align the chromosomes along the middle of the cell nucleus. This line is known as the metaphase plate. This allows the next phase to split the chromosomes evenly when they are separated.Image result for metaphase
  3. Anaphase - Each chromosome is split into two daughter chromosomes, which are then pulled to opposite sides of the cell. Polar microtubules, a kind of microtubule that makes up the spindle fibers, push against each other, causing the cell to elongate.Image result for anaphase
  4. Telophase - Chromatids arrive at opposite poles of the cell and new membranes form around the daughter nuclei. Then the chromosomes spread out and are unable to be seen. The spindle fibers also spread and are unable to be seen. Cytokinesis, the partitioning of the cell, may also begin during this stage.Image result for telophase
  5. Cytokinesis - In animal cells cytokinesis occurs 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 plants, however, cell plate is synthesized between the two daughter cells, eventually becoming a cell wall.Image result for cytokinesis