Lecture Notes for Sep 23, 2008

Mitosis process of Eukaryotic cell division daughter cells are identical, mitosis takes chromosomes, packages them and gives a copy to each daughter cell. (cytokinesis is the actual spliting of cells) must accurately copy information, segrgating chromosomes --> one copy into each cell --> makes each cell genetically identical Cell does not count or mark chromosomes, there is no way of ditinguishing. Cell makes sure of accuracy by keeping chromosome and its copy attached until the last minute. (this makes sure that each chromosome has a copy and makes sure it is where it belongs, not short and not too many) Microtubules (part of the cytoskeleton during interphase) reorganizes its structure to become the spindles, they pull chromosomes apart and seperate the copies, they also help in alignment. During interphase chromosomes are random and loose like spaghetti or a pile of rubber bands. Prophase ? chromosomes condense into tight springs (from the loose randomness they were before in interphase) ? nuclear membrane breaks down ? spindle is formed (from microtubules) "Prometaphase"- the end of prophase where the chromosomes attach to the spindle fibers. Metaphase all chromosomes are lined up at the center/ equator of the cell (metaphase plate if cut, they are around the perimeter) the chromosomes are held by tension pulling them in both directions, equal in the middle, they stop. this tension is similar to that of rubber bands being pulled. chromosomes are held to eachother with proteins. Anaphase the action! very rapid phase protease breaks the protein between the two chromosomes and breaks them apart. the tension from the spindle fibers (like rubber bands) will cause the chromosomes to "fling" back to the poles of the cell, or the opposite sides. Telophase (reverse prophase) ? dissemble spindles (form back into structural microtubules) ? decondense chromosomes ? reassemble nuclear membrane (remember there are two new ones in this cell, one on both ends) Cytokinesis (after Mitosis, the last part of M phase) one cell becomes two, each with its own plasma membrane Microfilaments- (part of the cytoskeleton during interphase is used like microtubules)- contracts and pinches off between the new nucleuses, this pinch will form the two new cells! Cells control a cell without control of its division is a cancer cell. some things are irreversable, once they have started the cell cannot stop or go back 1. DNA Replication- once they are replicated if the cell does not go through mitosis it will have too many DNA molecules, so if it does replicate it's DNA it must also divide. 2. Anaphase- the cell has no way of keeping track of which chromosome is which, so after they split from their copies they must continue the cell monitors these processes by having checkpoints/ stops to monitor the accuracy of the division and replication, it cannot stop the process however, they can stop one phase but the next will still go on, it doesnt need a go ahead from the previous step. ? G1- Gap 1 in interphase (irreversable) can pause and repair any damages made to the DNA during replication ? S- synthesis in interphase (irreversable) can pause to make sure DNA is replicating correctly ? G2- Gap 2 in interphase, only one that cell can reverse- can start prophase and still back out. makes sure all DNA has replicated, spindle making machinery is in place, and can pause and repair damages ? M- Metaphase (irreversable) makes sure the spindle has been built, all chromosomes are attached to spindle, and all chromosomes are aligned down the equator. it then gives the go ahead for anaphase (again it cannot stop it but measure accuracy)