BIO130H1 Chapter Notes - Chapter 4: Type Ii Topoisomerase, Dna Supercoil, Type I Topoisomerase
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BIO130H1 Full Course Notes
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Document Summary
Each eukaryotic chromosome contain a single, continuous dna molecule. The tip of each molecule are composed of a stretch of repeated sequence - telomere. The same telomere found throughout the vertebrae. The end replication problem : if they cannot replicate the ends of their dna. Required for the complete relocation of chromosome. Prevent the end of chromosomes from fusing with each other. Research show that the cells stop dividing entirely after about 50-80 doubling and entered a stage called replicative senescence. Decrease in the telomere repeats because most cells lack telomerase as they age indefinitely. Only cells that are able to resume expression of telomerase continue to proliferate. Without showing signs of the normal aging. Germs cells, stem cells retain telomerase activity. Telomerase shortening is a major factor of normal human aging. But it also protect human from cancer by limiting the number of divisions of a potential tumor cell. 90 percent of tumor contain an active telomerase enzyme.
