Lecture 1- the cell cycle

Lecture 1- the cell cycle - Cell Division: the Cell Cycle...

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Cell Division: the Cell Cycle The second half of this course deals with the problem of heredity. Although spontaneous generation, the generation of a living organism from inanimate matter without the help of another living organism, probably occurred at one time, about 4 billion years ago, it almost certainly has not occurred for several billion years. All organisms are now spawned by existing organisms. Moreover, the spawn almost always closely resemble their parents in all but the most superficial respects. Kangaroos give rise to more kangaroos and Kumquats give rise to more Kumquats. By the end of the course you should understand how Kumquats inherit Kumquatness from their parents. Ever since people understood the relationship between sex and reproduction, they have pondered the mystery of heredity. The Greek natural philosopher Aristotle (384BCE- 322BCE) understood that some "essence" was passed from male to female through semen, which combined with some female "essence" to give form to the resulting progeny. Over the following centuries there were unresolvable debates over the relative contribution of the male and the female. Some “preformationists” went so far as to propose that a tiny preformed human was transferred from the male. However, further understanding came only with the invention and exploitation of the microscope, primarily by Anton van Leeuwenhoek (1623-1723), and the discovery of cells. Eventually, scientists like Theodor Schwann (1810-1882) came to the conclusion that all organisms are made of cells. These cells divide to produce more cells. Moreover, the "essence" that must be transferred from a male to a female consists of cells, namely sperm, and these combine with cells present in the female, namely eggs. So, to a first approximation, cells are the units of heredity. So we must understand how cells divide to understand heredity. According to classical cell theory, one mother cell divides into two daughter cells . For cell division to be a productive use of the cell's time, both daughter cells must inherit from the mother cell everything they need to survive including the stuff of heredity a.k.a. the genetic material.
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We now know that cells are rather complicated little beasts full of stuff like proteins, carbohydrates, lipids, golgi, E.R. mitochondria etc. What more can we learn about where the genetic material might reside within a cell from studying cell division? Quite a lot it turns out. For one thing, cells spend a striking amount of their time and space dividing up their chromosomes . To understand what is so striking about this, we need to look more closely at how chromosomes are organized. One common way of looking at chromosomes involves a karyotype. The karyotype is just a way of staining and organizing chromosomes that makes patterns in their structure more apparent. The chromosomes for a karyotype come from dividing cells because only during division can you see chromosomes. A number of interesting things become apparent from looking at a karyotype.
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Lecture 1- the cell cycle - Cell Division: the Cell Cycle...

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