In 2001, the Nobel Prize in Physiology or Medicine was given to Leland Hartwell, Timothy Hunt and Paul Nurse for their discoveries of the key regulators of the cell cycle. This literature is the lecture given by Leland Hartwell on his Nobel Prize winning research as well as decades of research by a multitude of different scientists that led to the understanding of the cell cycle. In the lecture, Hartwell discusses the discovery of several important players in the cell cycle as well as their role, the effects of cell cycle mis-regulation, and the possible medical applications involving cancer treatment.
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Cyclohexanol was reacted via dehydration reaction in the presence of 85% phosphoric acid and cyclohexene was obtained in 28.1% yield. The product was identified to be cyclohexene via gas chromatography, IR spectroscopy and chemical testing. The presence of stretch at 1653 indicates a carbon-carbon double-bond, which would not be present in the starting material. The gas chromatography also did not show -OH band stretching at wavelength 3400-3500, which would have been seen in the starting material. IR spectroscopy also revealed only one compound to be present in essence, accounting for 99.95% of total area. Chemical bromine and potassium permanganate tests both indicated results congruent with those of an alkene (colorless when bromine solution added and brown precipitate formation when potassium permanganate added). Higher yield during distillation could be obtained by heating at a slower rate. Washing methods also could be altered to obtain a higher yield of product.
Product determined to be cyclohexene with a yield of 28.1%. The results of this experiment are summarized in the table below. Gas chromatography characterization was performed with two peaks being shown. One with a retention time of 0.349 and the other with a retention time of 0.396. The area of the second peak accounted for 99.95% of area, with the other accounting for 0.05% of total area. This indicates that the product sample used contained almost pure product, with very little second substance being detected. IR Spectrometry characterization was also performed. Analysis of IR spectrometry indicate characteristic absorptions of cyclohexene. A =C-H stretch is seen at a wavelength 3062, as well as a -C-H stretch between wavelength 3000-2800. A characteristic C=C stretch is also seen at wavelength of 1653. Also of note, -OH band stretching at frequency 3400-3350 is absent, which is a characteristic of the reactant cyclohexanol and is not present in the IR spectrometry of the product. All of these factors indicate the reaction product was cyclohexene and not cyclohexanol. Chemical tests were also performed to distinguish the product as an alkene from an alkane. In the dilute bromine solution, reaction product remained colorless and the negative control cyclohexane solution turned a reddish brown. In the potassium permanganate chemical test, the reaction product formed a brown precipitate, which is characteristic of an alkene, will the alkane control did not form any precipitate.
To a round-bottom flask placed in a 30mL beaker was added cyclohexanol (2.0 g, 0.02 mol) with 85% phosphoric acid (0.5mL). The solution was heated using a sand bath and distilled using a fractional distillation apparatus. Upon completion of fractional distillation, the solution was washed with water (1-2mL) and saturated aqueous sodium chloride (1-2mL). After washing solution, the organic layer was transferred to a clean vial and CaCl2 spheres were added. The vial was capped and the contents gently. The product of cyclohexene was allowed to dry for 5 minutes and a yield was obtained of (0.562g, 28.1%). Chemical tests were performed of the cyclohexene product. A 3% solution of bromine in dichloromethane added dropwise to cyclohexene solution (0.5mL). Separately, a 1% solution of potassium permanganate was added dropwise to cyclohexene solution (0.3mL). A gas chromatography and IR spectrometry were preformed to determine purity and properties of obtained product.
When chromosomal mis-segregation does occur however, the effects can be detrimental. This includes DNA damage that can occur due to cleavage furrow during cytokinesis. Mis-segregation also leads to increased p53 activity, which is a tumor suppressor protein that limits proliferation of cells. Aneuploidy can also lead to altered levels of gene expression due to a different amount of genetic material being present in the cell. One example of this is duplication of the APP gene, which encodes amyloid-B precursor protein being linked to early onset Alzheimer’s disease. Aneuploidy also leads to an increase in the transcription of proteins involved in stress response. In addition, aneuploidy can cause the misfolding of proteins, due to the overload that exceeds chaperone capacity. As we have discussed earlier, protein misfolding can lead to protein aggregation and a host of other issues.
Chromosome mis-segregation can lead to a number of physiological issues both in the short and long-term. The cause and effects of various chromosomal mis-segregation events and their molecular pathways are still not fully understood. Despite being shown to cause decreased cellular proliferation, aneuploidy is seen in an astounding 90% of solid tumors and 50% of blood cancers. Continued research is needed, however studies have shown that aneuploidy and CIN can both promote and inhibit tumorigenesis. A greater understanding of the role aneuploidy plays in tumorigenesis could shed light on the possible development of new cancer therapies in the future.
Chromosome mis-segregation can lead to a number of physiological issues both in the short and long-term and its effects are still not fully understood. Despite being shown to cause decreased cellular proliferation, aneuploidy is seen in an astounding 90% of solid tumors and 50% of blood cancers. Continued research is needed, however studies have shown that aneuploidy and CIN can both promote and inhibit tumorigenesis. A greater understanding of the role aneuploidy plays in tumorigenesis could shed light on the possible development of new cancer therapies in the future.
Aneuploidy is defined as the presence of an abnormal number of chromosomes in a cell. It does not however, include a difference of one or more complete sets of chromosomes which is defined as polyploidy. Aneuploidy has detrimental effects on the cell physiology, the integrity of the genome, and inflicts tremendous damage to DNA. For this reason, constitutional aneuploidy, or aneuploidy in every cell of an organism that originates from mis-segregation in germline cells is often lethal. One of the only exceptions in humans is trisomy of the 21st chromosome, which leads to Down’s Syndrome. Although aneuploidy severely interferes with the physiology of the cell, aneuploidy and chromosome instability has been paradoxically shown to cause the formation of tumors.
Chromosome mis-segregation and aneuploidy in somatic cells is an extremely rare event due to the cellular machinery in place to prevent it. The main player in ensuring chromosomes segregate properly during anaphase of mitosis is called the spindle assembly checkpoint. SAC is only silenced when amphiletic attachment of kinetochores to microtubules has occurred and anaphase commences. If incorrect attachment has occurred, SAC is turned on and recruits a host of different proteins including those of the MAD and BUB family, which catalyze the inhibition of APC/C that keeps the cell in metaphase. This highly conserved machinery leads to segregation with great fidelity.
This experiment, which is to be conducted by Steven Brewer’s Biology 312 class at the University of Massachusetts - Amherst, will aim to observe the effects of tree management techniques on a variety of factors. These factors include type of tree, number of tree cavities, number of dead branches, wildlife use, and understory diversity. The results of these observations will allow us to identify ways in which tree management techniques affect the surrounding ecology as well as the health of the tree. In the future, data drawn from this experiment can be used to improve tree management techniques both for the University as well as serve as a case study for other urban and school tree management protocols.