Topic 2 Molecular Genetics: Replication of the Telomere

Question 1

• Once the DNA has been replicated, we still need to replicate the telomeres, which are commonly termed the aglets of a chromosome since they protect the DNA from degradation by enzymes. However, throughout the replication of telomeres, there are two problems that can occur:

Answer 1

Note

Question 2

• There is not enough template strand for primase to attach

Answer 2

Problem 1

Question 3

• When the last primase is removed, and in order to change from RNA to DNA, there must be another DNA strand in front of the RNA primer. However, DNA polymerase cannot build after removing the RNA primer, so ultimately that RNA primer is destroyed by enzymes that degrade the RNA left on the DNA. A section of the telomere is subsequently lost with each replication cycle.
• Prokaryotes do not have this issue since their DNA is circular and doesn’t have telomeres

Answer 3

Problem 2

Question 4

• Telomerase is the enzyme that attaches to the end of the template strand and extends the template strand by adding a short repeating sequence of DNA that allows elongation of the lagging strand to continue. However, at the end of elongation, there will still not be enough of the strand for primase to attach, but this loss of an unimportant segment will not cause significant problems.
• Telomerase carries an RNA template and binds to the flanking 3’ end of the telomere that compliments part of its RNA, and synthesizes to fill in over the rest of its template

Answer 4

Note