Which structure prevents chromosome shortening during DNA replication?

During DNA replication, the ends of chromosomes can become progressively shorter due to the inability of DNA polymerase to completely replicate the ends of linear DNA molecules. Telomeres are specialized structures composed of repetitive nucleotide sequences that cap the ends of chromosomes. These protective sequences serve to prevent the loss of essential genetic information during the replication process.

As cells divide, the telomeres shorten instead of the actual coding regions of the chromosome, which preserves the integrity of the genetic material. Once telomeres reach a critically short length, the cell cycle is typically arrested, leading to cellular aging or senescence. Thus, telomeres play a crucial role in maintaining chromosome stability and length during the many rounds of DNA replication that occur in somatic cells.

The other structures mentioned do not directly prevent chromosome shortening: RNA primers initiate DNA synthesis but do not protect chromosome ends, Okazaki fragments are involved in the discontinuous synthesis of the lagging strand, and DNA ligase is responsible for sealing nicks between DNA fragments but does not address the shortening of chromosome ends.