Telomerization, prevention

While telomerase prevents telomere shortening in most eukaryotes, some organisms use alternative strategies. Drosophila species maintain telomere lengths by the regulated insertion of non-LTR retrotransposons into telomeres. This is one of the few Instances in which a mobile element has a specific function in its host organism. 

Figure 5 Interactions of end-binding proteins with telomeric G-rich overhangs. (A) Human POTl binding disrupts G-quadruplexes to allow extension by telomer-ase at the 3 end of a telomeric overhang. (B) The ciliate end-binding complex TEBPajfi promotes G-quadruplex formation to prevent telomere extension...

G-quadruplex formation to prevent telomere extension (compare Figure 5A and B). 

Fanti L., Giovinazzo G., Berloco M., and Pimpinelli S. 1998. The heterochromatin protein 1 prevents telomere fusions in Drosophila. Mol Cell 2 527-538. 

It has been suggested that zinc ions prevent formation of DNA quadruplexes containing guanine quartets by binding to the guanine N7 and 06. The quadruplexes are believed to be important to a number of areas of the genome including telomeres.179... 

Cancer ceDs often have relatively h%h levels of telomerase, preventing the telomeres ftom becoming shortened and contributing to the immortality of malignant cells. 

Starch is an abundant, inexpensive polysaccharide that is readily available from staple crops such as com or maize and is thus is mostly important as food. Industrially, starch is also widely used in papermaking, the production of adhesives or as additives in plastics. For a number of these applications, it is desirable to chemically modify the starch to increase its hydrophobicity. Starch modification can thus prevent retrodegradation improve gel texture, clarity and sheen improve film formation and stabilize emulsions [108], This may, for example, be achieved by partial acetylation, alkyl siliconation or esterification however, these methods typically require environmentally unfriendly stoichiometric reagents and produce waste. Catalytic modification, such as the palladium-catalyzed telomerization (Scheme 18), of starch may provide a green atom-efficient way for creating chemically modified starches. The physicochemical properties of thus modified starches are discussed by Bouquillon et al. [22]. 

Telomeres are the specialized structures at the ends of eukaryotic chromosomes. Their role is to prevent chromosomal degradation, end to-end fusion... 

The replication machinery alone cannot replicate the ends of linear DNA molecules, so a mechanism is required to prevent the loss of sequence information with each replication. Specialized structures called telomeres are added by another enzyme to maintain the information content at chromosome ends. 

For additional information, reference may be made to the volume by Life Extension Foundation (2003). It should also be mentioned that this volume has the following chapter or section titles Cancer Overview of Protocols Cancer Adjuvant Therapies Cancer Chemotherapy Cancer Clinics Offering Alternative Therapies and Cancer Gene Therapies, Stem Cells, Telomeres, and Cytokines. There are also chapters or sections titled Cancer Prevention Cancer Radiation Therapy ... 

A FIGURE 10-27 Microscopic appearance of typical metaphase chromosome. Each chromosome has replicated and comprises two chromatids, each containing one of two identical DNA molecules. The centromere, where the chromatids are attached, is required for their separation late in mitosis. Special telomere sequences at the ends function in preventing chromosome shortening. 

Addition of Telomeric Sequences by Telomerase Prevents Shortening of Chromosomes... 

The story of the Hayflick limit came to a head in 1990, when Cal Harley, founder of the Californian biotechnology company Geron Corporation, made a connection between the ability of cells to count and the length of their telomeres — the tips at the ends of individual chromosomes. Telomeres are often said to resemble the ends of a shoelace — their purpose is to prevent fraying in other words, to preserve the integrity of the chromosome. They are also said to be the secret of eternal life. They are not, as we shall see. 

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