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Ch.24 Genes and Chromosomes, Organization of information in chromosomes,…

- - - - • Region where the chromatids are held together during mitosis — that is, after DNA replication but before cell division
      - • Essential for equal distribution of chromosome sets to daughter cells
      - • Have AT-rich repeated sequences of N 130 bp
    - - • May form special loop structures to keep DNA ends from unraveling — contain multiple repeats with general sequence
      - • (T G ) (A C ) where n = 1500 or more in mammals — added by enzyme telomerase (protein+nucleotides)
      - Telomeres Are Associated with Cellular Aging
        
        • In many tissues, telomeres are shortened after each round of replication.
        
        • Thus, the cellular DNA "ages."
        
        • Normal human cells divide about 52 times before losing the ability to divide again (Hayflick limit).
- - - - Lk = Tw+ Wr
        
        Writhe (Wr) is the # coils
        — typically a negative value
        
        Twist (Tw) is the # twists or turns of the helix