A. Chapter Summary
What Chapter Fifteen deals with is cellular division which, you know, is essential to life. If our cells weren't to divide or replicate, ultimately, our bodies... Well, our bodies wouldn't even be here in the first place. Moving along, in the first section, it deals with what can be learned from karyotypes (which reveal the number, size and form of chromosomes found within an actively dividing cell). Chromosomes occur in sets; for example, human chromosomes contains 23 different types of chromosomes and can be listed by size (but not applied to the sex chromosomes--the ones that determine gender. When a cell carries two sets of chromosomes, the organism is of the cell is said to be diploid (2n) where n equals 23. Gametes, however, which are the sperm and egg cells, are haploid and only contain one set of cells. When diploid, the pairs of chromosomes are called homologues.
Cells also go through a cell cycle where they grow, expand and explode divide. There are four phases of the cell cycle: G1, S (synthesis of DNA), G2 and M phase (mitosis and cytokinesis). The first three are known as interphase, where the cells grows and copies the chromosomes, preparing for cell division. However, cells may exit the cell cycle and remain for long periods of time, which is known as the G0--where cell has postponed making a decision to divide or never divide again. This cell cycle is controlled by checkpoint proteins known as cyclins and cyclin-dependent kinases, which will be used to make sure that if a cell messes up, it doesn't have to repeat the cycle but rather go back to the checkpoint it last passed (much like a video game).
In mitotic cell division, which is asexual, there are phases that it has to go through: interphase, prophase, metaphase, anaphase and telophase. In prophase, the chromosomes are already condensed and the centrioles (which will pull apart the chromosomes) begin to separate at opposite poles. In metaphase, the centrioles line up the chromosomes by the centromeres (which hold together sister chromatids). During anaphase, the chromosomes are pulled apart to their separate ends. In telophase, a clevage furrow intercepts the cell while a new nucleus forms around the chromosomes in each set, creating two separate cells.
Meiosis is different, however. These are needed for sexual reproduction and replicating the sperm and egg cells. In ways, it is like mitosis but the original cell must divide into four different types of cell. The diploid cell contains homologous pairs, for simplicity sake, the mother and father chromosomes. When they're condensed, they are then lined up in metaphase I, when crossing over (that is, when a father's chromosomes can mix with the mother's chromosomes) before they are pulled apart in anaphse I. When they are separated in telophase I, they begin for metaphase II, where they line up again to be pulled apart by the centrioles in anaphase II, ending at telophase II with four, different chromosomes.
B. Useful Material
Since this chapter is about mitosis and meiosis (essentially, cell division) I did my not so extensive research on Cracked which led me to this article about Henrietta Lacks, the reason for HeLa cells. As the Cracked article oh-so-eloquently put it, it's like having a bunch of cells but they were all Wolverine-fied. In other words, these cells came from an immortal cell line and, once they underwent cell division could be kept alive and grow even out of the human they came from. These Wolverine cells were named HeLa cells were used to fight cancer, flu and Parkinson's disease. Basically, these cells remade the medicine world.
Oh, I forgot to rage, which this link needs. Because Henrietta Lacks, before her death, was subjected to horrible and grotesque testing because of the fact that she had cervical cancer. So, scientists decided that her body could be used as a guinea pig and continuously used for research. Not only that, even though her cells were amazing and helped the medicine world, they were taken from her without consent. Without consent.
So, I'll keep in my harsh and tart words to say this instead. Henrietta Lacks, thank you so much for these cells--the ones that evolved our medicinal world--that people took away from you.

This picture. It's mitosis. Well, that's the simple and lazy way of describing what this picture is (though, it does a pretty good job of explaining itself). So, anyway, the second stage has to do with early prophase and the chromosomes condense while the centrioles begin to separate. During late prophase, the centrioles are at the opposite ends and cause the line up of chromosomes (metaphase begins). During the early stages of anaphase, the centrioles pull them, the chromosomes apart, while in the later stage, the chromosomes have reached their respective ends and begin to have a membrane surround them (telophase). Once the cell cleaves, there are two different cells. When you think about this, how are cells always live, divide, die and then revert to live again, doesn't that make our bodies completely something else since they're not our original selves? So, can we say that we're truly ourselves? Oh, Locke's Socks, I love it.
So, here we are again at the PubMed article. This one talks about how the retinoblastoma tumor suppressor (RB) pathway is necessary for stopping and holding back proliferation and surpressing tumor development in a number of tissues. When RB deletion occurred in the liver of an adult mice, it led to DNA replication in the absence of productive mitotic condensation. This replication was E2F-mediated and associated with DNA damage as well as a nontranscriptional G2/checkpoint, targeting the accumulation of Cyclin B1. Essentially, RB has the critical role of controlling the cell cycle transitions.
Comments (1)
Derek Weber said
at 2:47 am on Apr 1, 2011
nice
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