# Mitosis --- **Mitosis** is a type of [[cell division]] for [[cell#Somatic Cells vs Gametes|somatic cells]]. The goal of mitosis is to preserve the genetic material and coply exactly what you started with as accurately as possible, including having the daughter cells retain the same number of chromosomes as the parent cells. As these things go, it is pretty straightforward. **[[Microtubules]]** do a *lot* of the work in mitosis. There are a lot of moving pieces to account for and wrangle up. **[[cytoskeleton|Actin]]** is responsible for pinching off the shape of the cell at the end. ![[mitosis.png]] Before mitosis can begin, the cell must undergo [[DNA replication]], which happens during the [[cell cycle|S phase]] of the cell cycle. Newly eplicated chromosomes are condensed into [[chromatid|sister chromatids]] which are, at this point, joined along their length by proteins called "cohesins". Mitosis is followed by [[cytokinesis]]. ![[interphase.png]] There are 4 phases of mitosis: prophase, metaphase, anaphase and telophase. Even though they are classified as such, bear in mind that it is a fluid process that doesn't have ridgedly defined starts and stops. ## Prophase **Prophase** ("early"-"stage") is the phase that kicks off mitois, which starts with the replicated mess of spagetti DNA and ends with the neat bundles that are [[chromosome|chromosomes]]. In **early prophase** the cohesins go away, leaving the [[chromatid|sister chromatids]] bound together only by a single point the the middle called a [[chromosome|centromere]] in that classic X structure we see so often. (It's important to remember that when it is in this X form, it is one, replicated chromosome, not a homologous pair.) **Spindle apparatuses** are formed during prophase, which are the structures made out of [[microtubules]], that can move the chromosomes around, and will eventually pull the sister chromatids apart. ![[prophase.png]] In the **late prophase** or **prometaphase** ("before"-"metaphase") the [[nucleus|nuclear envelope]] disintegrates and microtubles attach to each chromosome at special structures on the surface of the centromere called "kinetochores" located on each sister chromatid. Each sister chormatid is attached by these microtubles to a [[centrosome]] on opposite ends of the cell. ![[prometaphase.png]] ## Metaphase During **metaphase** ("adjacent or between" -stage") the microtubles maneuver the chromosomes along the middle of the cell, on an invisable line refered to as the "metaphase plate". During mitosis, there is no particular order that they chromosomes line up, as we do not care about [[meiosis i|independent assortment]]. Tug of war begins. ![[metaphase.png]] ## Anaphase During **anaphase** ("back"-"stage") the centromere holding the sister chromatids together is pulled apart. Each chromatid is pulled to the [[centrosome]] at opposite ends of the cell. This is the moment that the number of chromosomes in the cell double. ![[anaphase.png]] ## Telophase During **telophase** ("away"-"stage") the [[nucleus|nuclear envelope]] around the new sets of chormosomes. When the two new nuclei are fully formed, this marks the end of mitosis. ![[telophase.png]] ___