Mitosis Cellular Reproduction Part I
Cells must reproduce, the cell cycle describes how cells reproduce and what regulates reproduction. All somatic cells (non sex cells) go through the cell cycle. It takes about 24 hours for human cells to go through the cell cycle. Some organisms complete the cycle in about 8 minutes! Cells spend most of their time in interphase (23 hours for humans). The M-phase occurs over a shorter period of time (1 hour for humans). http://www.youtube.com/watch? v=gtz_vj-hdzm&safe=active The Cell Cycle
Interphase DNA is in the form of Chromatin. The cell is metabolically active and the DNA is very loose so that DNA synthesis and other processes that require access to the DNA can occur. The nuclear membrane is visible and intact. In most cells the nucleoid region of the nucleus is visible as a dense dark dot inside the nucleus. The majority of cells are any given time are in interphase. Interphase is the longest phase of the cell cycle in every known species.
Mitosis/ M-Phase Chromosomes become visible. Chromosomes are condensed structure of DNA. Chromosomes condense and the cell undergoes the stages of mitosis the result is two identical cells. This phase of the cell cycle take a short amount of time that varies by species and organism age.
The chromosomes begin to condense and form string like strictures that are visible in the nucleus. The nuclear envelope begins to dissolve and the centrioles begin to move to the poles of the cell to start directing the division. Prophase
Metaphase In metaphase the chromosomes in the fully condensed form line up on the equator of the cell called the metaphase plate. The centrosomes send out spindle fibers (made of microtubules) to attach to the chromosomes, this structure is called the aster. The spindle fibers pull on the chromosomes at their centromere. Homologous chromosomes are help together at the centromere until the pulling begins.
In this stage the aster structure begins to pull the homologous chromosome pairs apart to the poles of the cell. This pulling tension signals the other cellular components to head to the poles of the cell. Once anaphase is complete the spindle fibers will detach and the nuclear envelop will reform. Anaphase
Telophase/Cytokinesis The cellular organelles and the chromosomes are now at home in their new cells. The cells are identical. The nuclear envelop is reformed and the cell pulls the cell membrane inward to create a cleavage furrow. This will trigger the self sealing properties of the membrane to eventually form a new membrane in between the cells. This is cytokinesis.
Growth and Reproduction Regulators Growth Regulators There are 3 check points that must be passed if cell division is to occur. If the cell fails at any of the checkpoints it will enter into programmed cell death or be repaired. G1/S- sure the cell has sufficient organelles and other cellular components for cell division. Some cells enter a rest period if division is not necessary at this checkpoint called G0. G2/M- makes sure that the DNA synthesized in the S phase is correct and not mutated. If a mutation is found it is repaired before the M phase begins. If it is very large mutation the cell will go into programmed cell death. Metaphase- makes sure that the chromosomes have aligned correctly on the metaphase plate and at attached to the correct spindle fiber. The tension on the fibers is the determining factor is whether this checkpoint is passed or not. http://www.youtube.com/watch?v=1eb8q9ar8hk&safe=active Unregulated Growth Cells that have mutated and no longer obey the cell cycle grow and replicate uncontrolled. This is cancer. This unchecked growth and reproduction funnels cell resources from healthy cells and worsens the impact. Cancer cells consume cellular resources 3 times faster than normal cells. http://www.youtube.com/watch?v=ieuanxfvxkc&safe=active http://www.youtube.com/watch?v=lepttolebqo
Overview The cell cycle regulates reproduction. The cell cycle has two phases: Interphase and M-phase Interphase has three stages: G1, S, G2 M-Phase has five stages: Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis. You can identify the stages of the M-phase by the shape of the chromosomes. The cell goes through three check points to check for mistakes in replication or other errors. G1/S, G2/M and Metaphase. If cells lose their ability to regulate growth they become cancer. http://www.youtube.com/watch?v=l0k-enzoeom&safe=active http://www.youtube.com/watch?v=c6hn3sa0ip0&safe=active http://www.youtube.com/watch?v=vln7k1-9qb0&safe=active