Week 7 Notes
Week 7 Notes BSC 114
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This 2 page Class Notes was uploaded by Rebecca Sharp on Thursday March 24, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Stevan Marcus in Winter 2016. Since its upload, it has received 18 views. For similar materials see Principles Of Biology I in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 03/24/16
Welcome to the Cell Cycle! Cells can either be ‘gametes’, reproductive cells like egg or sperm cells have only half the chomosomes that somatic cells do. Somatic cells are body cells, they have two or more sets of chromosomes Cellular DNA Hollistically, it’s called the cell’s genome and in eukaryotes, it’s stored in the nucleus A ‘chromosome’ is the word for packaged DNA and it’s assorted proteins. Chromosomes get condensed into chromatin. During cell division, even the chromatin gets squished. Get to Know Your Chromosomes Traditionally, they’re shown in pairs, looking like an X. These are called ‘sister chromatids’. A chromosome becomes a pair of sister chromatids after DNA replication takes place. The place in the middle, where they intersect is called the ‘centrosome’. It comes apart during cell division. One set of DNA goes to each daughter cell. Cell Division: Basically Cells can divide via meiosis or by mitosis and cytokinesis. o Meiosis is the process by which gametes reproduce, each daughter cell ends up with only half the DNA information. o Mitosis is the division of genetic material in the nucleus of eukaryotic cells o Cytokinesis is the process by which the cytoplasm reproduces itself and then splits in to two daughter cells In somatic cells, there’s two major parts of the cell cycle: the mitotic phase (M Phase) which consists of mitosis and cytokinesis, and interphase, which consists of the cell growing up and getting ready for cell division. Cell Division: But in More Detail Moves from G1 to S to G2 to M, and then starts back over. G1 is Gap One, during which the cell grows and listens carefully to environmental signals to figure out if it’s okay to divide or not. S is when the cell decides okay, this is a good time to start dividing, and begins to replicate its DNA G2 is Gap Two, during which the cell takes a break to step back and make sure now is a good time to divide, and begins to start forming the mitotic spindle M is the Mitotic Phase, during which all the good stuff happens o The M Phase actually consists of 5 mini-phases; Prophase, Prometaphase, Metaphase, Anaphase, and Telophase. o Prophase is where the early mitotic spindle forms, and the chromosomes begin to condense o Prometaphase is when the nuclear envelope breaks open, giving the sister chromosomes access to the mitotic spindle o Metaphase is when the sister chromosomes are aligning on the metaphase plate A quick word about the metaphase plate; it’s an imaginary plane in the center of the microtubules that make up the mitotic spindle. The microtubules are either kinetochore (non-overlapping) or non-kinetochore (overlapping). The chromosomes attach themselves at the centromere (the intersecting part of the X) to the kinetochore microtubules. o Anaphase is when the kinetochore shorten, pulling the sister chromosomes apart to opposite sides of the cell o Telophase is the part where the nuclear envelope begins to form cleavage and a nucleus forms around the genetic material Cytokinesis is the part where a contractile ring pinches the cell into two daughter cells Regulating the Cell Cycle The cell has several checkpoints throughout the cell cycle to regulate. The first is towards the end of G1, the second is at the very end of G2, and the third is between Metaphase and Anaphase in M. Available nutrients, cell growth, and protein kinases all serve as signals to the cell as to whether it’s okay to divide or not The checkpoints were not all created equal, G1 is the most important. Usually if a cell passes the G1 check point, it also crosses the finish line and divides. If the environment isn’t conducive to division, it doesn’t pass the G1 checkpoint, it moves into a non-dividing phase called G0. To pass the G2 checkpoint, the environment must still be favorable and all of the DNA must be replicated. To pass the M checkpoint, all the chromosomes must be attached to the spindle and the environment must still be conducive to replication. The next big regulator, after the checkpoints, are cyclin-dependent kinases. CDKs do absolutely nothing unless they’re stuck to a cyclin protein. CDKs are controlled by other protein kinases, protein phosphatases, and protein-protein interactions. They’re called cyclin because they go through a cycle of synthesis and degradation through each cell cycle. These events trigger other necessary events in the cell. There’s four kinds: o G1 cyclins send the cell into the growth in G1 o G1/S cyclins commit the cell to the process of DNA replication o S cyclins initiate DNA replication o M cyclins drive mitosis