Genetics: Analysis and Principles 5th Edition by Robert Brooker

تمرين 33

As shown in Figure 11.23, telomerase attaches additional DNA, 6 nucleotides at a time, to the ends of eukaryotic chromosomes. However, it makes only one DNA strand. Describe how the opposite strand is replicated.FIGURE 11.23 The enzymatic action of telomerase. A short, 3-nucleotide segment of RNA within telomerase causes it to bind to the 3 overhang. The adjacent part of the RNA is used as a template to make a short, 6-nucleotide repeat of DNA. After the repeat is made, telomerase moves 6 nucleotides to the right and then synthesizes another repeat. This process is repeated many times to lengthen the top strand shown in this figure. The bottom strand is made by DNA polymerase, using an RNA primer at the end of the chromosome that is complementary to the telomeric repeat sequence in the top strand. DNA polymerase fills in the region, which is sealed by ligase. Note: Though not shown in the figure, the RNA primer is eventually removed, which leaves a 3 overhang.