4.17.2007 - 4.17.2007 Interphase Gap one is first part of...

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4.17.2007 Interphase Gap one is first part of interphase a lot of protein synthesis going on Outside of the circle is what a chromosome in that stage looks like Euchromatin is relatively decondensed, very long and spindly in interphase (but that gives us a bad picture so they are condensed in the picture even though really not so) In Gap I there is a chromosome that is just a single molecule of DNA, the pinch is where the centromere is When you picture a chromosome you picture it as the X, what it is in cell division o This chromosome has two double stranded DNA molecules instead of just one as it is in GI o It consists of 2 chromatids connected to each other at the centromere o Each chromatid is one double stranded DNA molecule bound up with a whole bunch of protein In Gap I o One chromatid, one double stranded DNA molecule There is a decision point after Gap I where it might just stay in Gap I and not go on, this is where cells spend most of their time, but if the cell does commit itself to undergo replication it goes onto S phase It is commited to replication and cell division if it decides to go on In S: the two strands separate and each one is used as a template so you end up with two double stranded molecules, each one binds up with a whole bunch of protein to make two chromatids. These stay attached to each other at the centromere. After replication you have two chromatids per chromosome, before the replication there is just one chromatid per chromosome. In G and in S you have one chromosome. As long as the two chromatids remain attached at the centromere it is still one chromosome In Gap II there is a lot more protein synthesis because there are a lot of proteins needed in cell division, here the cell gears up for cell division M: mitosis, division of genetic material and division of the cell o Two chromatids separate from each other, now two chromosomes because separated o Each chromatid/chromosome goes to a different cell and goes through the cell cycle again Don’t need to know about centrioles, spindle fibers, etc for the test, DO need to know what are the chromosomes doing, what alleles are going where to understand what meiosis and mitosis have to do with inheritance and genetic makeup of the cells that result Prophase of mitosis o Spindle fibers attach to the chromosomes o Spindle fibers from one pole attach to one kinetochore of a chromosme o The other kinetochore of that chromosome (on the other chromatid…each chromatid has a kinetochore) will attach to spindle fibers from the opposite pole o Spindle fibers from one pole attach to one kinetochore on a chromosome o The other kinetochore on the other chromatin will attach to spindle fibers on the opposite pole o Spindle fibers are just out there and chromsomes are moving around the cell – when a kinetochore makes contact with a spindle fiber it is random, but it just holds one once it does o If it doesn’t happen in this way then the kinetochores let go and the process restarts for that chromosome
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4.17.2007 - 4.17.2007 Interphase Gap one is first part of...

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