Lecture 11 - Lecture11 1. 2.

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Lecture 11 The telomere has two functions: 1. To protect the chromosome end from both degradation by nucleases and to seal it so it does not initiate recombination reaction which leads to translocation and genome instability 2. To allow the telomere to be extended so sequences are not successively lost from the ends each replication cycle Telomerase Play a crucial role regulating the cell cycle, preventing genomic instability lack of somatic cells is probably the major force for aging and senescence. reactivation of telomerase is the cause for tumors and cancer cells Telomerase is the enzyme that creates the repeats and proteins that binds to the repeats. Free ends are very recombinogenic, they use non-homologous recombination. Any time proteins recognize the free ends, they invade the nick and cause free end displacement and initiate recom- bination. If you don’t seal the ends of your chromosome and have a break due to damage or sheer. If you don’t have telomeres, then the free ends invade every time there is a nick and you end up with lots of translocations and recombination events. Sealing the ends of chromosomes is one of the key functions of the telomere Fig 28.16, 28.27 telomere have simple repeating sequences the telomere is required for the stability of the chromosome end A telomere consists of a simple repeat when a C+A rich strand has the sequence C 41 (A/T) 1-4 Blasco paper Telomerase extends the ends of DNA because the 5’ ends have the phosphates and the 3’ ends have the free OH
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On the 3’ end either there is a loop formed or it is primed All telomeres have a GT rich strand CA rich strand The telomerase is the RNA subunit of the telomerase itself carries two hexameric repeats that are used to align to the end of the chromosomes and pairs then allows for its own catalytic subunit to synthesize nucleotides using the RNA as the template 2 strands one GT rich and one CA rich the two repeats in the telomerase itself, do they represent GT or CA rich strand? RNA is going to be the template that is carried by the telomerase itself being CA rich because your synthesizing the GT rich template so the complement strand must be CA rich even though telomerase is a DNA polymerase it actually is another example of reverse transcriptase because it is using RNA the template to synthesize DNA. The telomeric strand is longer than the complementing strand
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Lecture 11 - Lecture11 1. 2.

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