Question

The ends of linear chromosomes are difficult to replicate

A. Describe the problems associated with replicating the ends.        

B.

1. To avoid the loss of terminal sequences different organisms use different strategies to replicate their DNA.
   1. What features of the chromosome does E. coli have to circumvent this problem? Provide a detailed answer.
   2. What strategy do prokaryotes use to replicate linear chromosomes to circumvent this problem?  Provide a detailed answer
   3. What strategy do eukaryote use to replicate chromosomes to circumvent this problem? Provide a detailed answer.          

Answer 1

Ans .(A) Problems associated with replicating the ends :-

During the chromosome replication, the enzymes that duplicate DNA cannot continue their duplication all the way to the end of a chromosome, so in each duplication the end of the chromosome is shortened ( this is because the synthesis of Okazaki fragments requires RNA primers attaching ahead on the lagging strand).

Ans .(1) In E.coli

E.coli contain a single circular DNA molecule that makes up their entire genome. There are no free ends to DNA.

Ans .(ii) In Prokaryotes

In prokaryotes, the end - replication problem is solved by having circular DNA molecules as chromosomes. Another cause of telomere shortening is oxidative stress.

Ans .(iii) In Eukaryotes

Eukaryotes has solved the end - replication problem by locating highly repeated DNA sequence at the end, or telomeres, of each linear chromosome.