What is a telomere?

A telomere is best defined as a nucleotide sequence at the end of chromatids. Telomeres consist of repetitive sequences of DNA that protect the ends of chromosomes from deterioration or from fusion with neighboring chromosomes. This protective function is crucial because, during DNA replication, the enzymes that duplicate DNA cannot replicate the very ends of the linear chromosomes, leading to progressive shortening of chromosomes with each cell division. Telomeres act as a buffer zone to ensure that important coding regions of DNA are not lost.

The other choices do not accurately represent what telomeres are. For instance, while proteins do play a role in DNA stability, they are not specifically what a telomere is. Additionally, the binding of RNA to DNA is related more to processes like transcription, not the protective chromosome ends. Finally, coding DNA refers to segments that code for proteins, which contrasts with the non-coding, repetitive nature of telomeres that function mainly in protection rather than in coding for genes.