Prophase 145563 224147248 2008-07-07T15:10:13Z 70.184.236.141 /* Prophase in plant cells */ <!-- Deleted image removed: [[Image:Prophase-flourescent.jpg|thumb|right|251px|Newt lung cell in Prophase, with the [[mitotic spindle]]s [[staining (biology)|stained]] green and the [[cell nucleus]] and [[chromatin]] stained blue.]] --> [[Image:Prophase.jpg|thumb|right|151px|An illustration of prophase in [[Gray's Anatomy]]. The chromatin has condensed.]] '''Prophase''' is a stage of [[mitosis]] in which the [[chromatin]] condenses into a highly ordered structure called a [[chromosome]] (it is at this stage giemsa staining can be applied to elicit G-banding in chromosomes). This process, called ''chromatin condensation'', is mediated by the [[condensin]] complex. Since the genetic material has been duplicated, there are two identical copies of each chromosome in the cell. Identical chromosomes, called sister chromatids, are attached to each other at a DNA element present on every chromosome called the [[centromere]]. When chromosomes are paired up and attached, each individual chromosome in the pair is called a [[chromatid]], while the whole unit is called a chromosome. When the chromatids separate, they are no longer called chromatids, but are called chromosomes again. The task of mitosis is to assure that only one copy of each sister chromatid goes to each daughter cell after cell division. An important organelle in mitosis is the [[centrosome]], the microtubule organizing center in metazoans. During prophase, the two centrosomes, which replicate independently of mitosis, have their [[microtubule]]-nucleating activity increased due to the recruitement of γ-tubulin. The centrosomes will be pushed apart to opposite ends of the cell nucleus by the action of [[molecular motor]]s acting on the microtubules. The nuclear envelope breaks down to allow the microtubules to reach the [[kinetochore]]s on the chromosomes. The nuclear envelope break down marks the end of prophase. [[Prometaphase]], the next step of mitosis will see the chromosome being captured by the microtubules. ==Prophase in plant cells== In this first phase of mitosis, the cells of higher plants (such as the flowering plants) undergo a series of events preparing them for mitosis before the onset of prophase. In highly vacuolated plant cells, the nucleus has to migrate into the center of the cell before mitosis can begin. This is achieved during the [[G2 phase]] of the cell cycle through the formation of a [[phragmosome]], a transverse sheet of cytoplasm that bisects the cell along the future plane of cell division. Prophase in plant cells is preceded by a [[preprophase]] stage only found in plants. Preprophase is characterized by the formation of a ring of microtubules and actin filaments (called [[preprophase band]]) underneath the plasmamembrane around the equatorial plane of the future mitotic spindle and predicting the position of [[cell plate]] fusion during [[telophase]]. The preprophase band disappears during nuclear envelope disassembly and spindle formation in prometaphase despite contrary belief The cells of higher plants lack centrioles. Instead, the nuclear envelope serves as a [[microtubule organizing center]]. Spindle microtubules aggregate on the surface of the nuclear envelope during preprophase and prophase, forming the ''prophase spindle''.<ref>{{cite book | last = Raven | first = Peter H. | coauthors = Ray F. Evert, Susan E. Eichhorn | title = Biology of Plants, 7th Edition | publisher = W.H. Freeman and Company Publishers | date = 2005 | location = New York | pages = 58-67 | isbn = 0-7167-1007-2}}</ref> {{Cell cycle}} ==References== <references /> [[Category:Mitosis]] [[de:Prophase]] [[es:Profase]] [[fr:Prophase]] [[it:Profase]] [[lt:Profazė]] [[nl:Profase]] [[pt:Prófase]]