First, some review…
y Mitosis is responsible for the duplication of existing eukaryotic cells to create new ones.
y Mitosis consists of different phases, Prophase, Metaphase, Anaphase, and Telophase.
y The concept of Mitosis focuses on the chromosomes in the cell, rather than the cytoplasm.
y Mitosis accounts for only ten percent of the cell cycle’s time. The rest is mostly the cell growing to prepare for the next division.
Prophase
y First stage of mitosis
y Chromatin (loose genetic material) condenses into chromosomes, which are far smaller. The cell has previously made a copy of it’s DNA, so there is one chromosome made of two identical sister chromatids.
y Each pair of chromatids are connected by a centromere.
y Near the nucleus are centrosomes, structures that direct microtubules that will manipulate the DNA
y Nuclear membrane breaks down
Metaphase
y Second stage of mitosis.
y Chromosomes align themselves in the middle of the cell.
y Microtubules from the centrosomes attach to kinetochores, a specific protein on the centromere. Each chromatid has it’s own kinetochore. These are very important, as they are the only points on the chromatids that can be acted on by the microtubules (mitotic spindles).
Anaphase
y The third stage of mitosis.
y At this point, the mitotic spindles pull sharply on the kinetochores, separating the chromatids. y The spindles begin to pull the chromatids away from each other towards opposite ends of the cell.
Telophase
y Final stage of mitosis.
y Telophase is essentially the reversal of prophase, the remains of the nucleus reforms around each set of DNA.
y All that remains is cytokinesis, where the cytoplasm itself divides. This is done through a ring of fibres that contract around the middle of the cell, slicing it into two.
And Why Does This Matter?
y Mitosis accounts for the creation of almost of the cells in your body. It is important that we understand this tremendously essential process. y What happens when mistakes happen?
Cancer: The Basics
y Cells monitor the progress of mitosis using various chemicals. This allows mitosis and cell division to occur faster or slower based on what the body needs. For example, mitosis will occur faster to grow skin cells over a wound, or slow down when the body is nutrient‐
deficient.
y This control may be lost, leading to cells that divide rapidly and often with harmful effects.
y N‐K cells in white blood cells kill cancer
The Basics: Continued
y The creation of cancerous cells can occur naturally through mitosis. Other times, cancer will be brought on by carcinogens and the environment.
y Either way, the cancer is caused by mutations in the DNA.
y Mutations in general aren’t bad. Evolution of species and adaptations to environments depend on mutations to actually cause lasting changes to an organism.
Mutations
y Mutations are variations in the DNA of the organism. They can occur through natural selection (involves miotic reproduction) or through environmental causes. The latter causes mutations that, if they are not repaired, can propagate and create new mutated cells. This division can go out of control if the genes that are infected include oncogenes and tumor suppressor genes, which stop cancerous tumors from growing.
How Mitosis Can Work For You
y Our bodies will always need new cells as long as we live. Cells die naturally (through apoptosis and autophagic pathways, among others) and through environmental causes, such as physical trauma like getting a cut.
y These cells need replacement, as billions die daily. Mitosis serves two functions in humans: Growth, and Repair.
Growth and Repair
y Firstly, tissues need to be built on at several points throughout a human’s life. The most obvious occurrence of growth is during childhood, where the body grows from one cell at conception to around 100 trillion upon reaching adulthood. Considering that cell death will occur often, MANY replications will need to take place over the next two decades to reach this high number.
Growth Continued
y Growth also occurs to increase the amount of a particular kind of tissue, such as muscle. These kinds of growth can occur at any time during a human’s life, but are notably more dramatic during or soon after puberty.
y Cell growth needs to be moderate, as too little with lead to atrophy and too much leads to cancer.
Tissue Repair
y The body’s ability to repair itself is essential to our survival. Otherwise, your first injury, be it a paper cut or fall off of a bike, could have lead to a serious long term injury or death. The body repairs its tissues through mitosis. Another very important example is in our stomach. The acid there eats through the cells that line the stomach. This lining has to be replaced every few days to contain that acid.
Cell One
Cell Two