The Cell Cycle Notes PDF

The Cell Cycle The Cell Cycle is the term used to describe the life cycle of a cell. The life of a cell can be broken into 2 main categories: 1. Interphase – This is described as the time frame when the cell is not dividing, but is actually the busiest time of a cell’s life. It also make...

The Cell Cycle The Cell Cycle is the term used to describe the life cycle of a cell. The life of a cell can be broken into 2 main categories: 1. Interphase – This is described as the time frame when the cell is not dividing, but is actually the busiest time of a cell’s life. It also makes up the bulk of a cell’s life. (75%) During this phase, the nucleus and nucleolus are clearly visible. All of the normal life functions are occurring (making ATP, protein synthesis, etc.) Chromatin are thin and tangled. Interphase is made up of 3 smaller phases. 1. G1 (Cell Growth) – The number of organelles and amount of cytoplasm increase 2. S Phase (DNA Replication) – The chromosomes replicate, or produce identical copies of themselves. The identical copies of the chromosomes remain held together by a centromere. Collectively, they are referred to as Sister Chromatids. Eventhough these chromatids exist, they are too thin to be visible. 3. G2 (Preparation for Mitosis) – The cell makes organelles and substances for the upcoming cell division. 2. Cell Division – This divided into 2 main steps, Mitosis and Cytokinesis. a. Mitosis – This is a series of phases involving one nucleus dividing into two identical nuclei. i. Prophase – The nucleolus and nuclear envelope begin to disappear. Chromosomes thicken and become visible as Sister Chromatids. The centrioles move to opposite ends of the cell. Microtubules that make up the spindle fibers begin to appear and connect the centrioles to the centromeres of each sister chromatid. The nuclear envelope begins to dissolve. ii. Metaphase – The chromosomes are moved to the center of the cell by the spindle fibers connected to the centromeres.  iii. Anaphase – The sister chromatids are separated at the centromere by the pulling spindle fibers and migrate to the opposite ends of the cell. Each chromatid is now a separate chromosome. iv. Telophase – The chromosomes reach the poles and two separate nuclei begin to form. A cleavage furrow begins to form as the cell membrane pinches and cytokinesis begins. b. Cytokinesis – Cell begins to split. The cytoplasm splits. In plants, a cell plate forms to divide the cell. In animal cells, plasma membrane pinches apart. The nucleolus and nuclear membrane reappear. Chromosomes uncoil back into chromatin. We now have two identical Diploid daughter cells. Interphase The same process, but as it occurs in a plant cell.