Describe the function of telomerase in DNA replication.

Telomerase is an enzyme that adds DNA sequence repeats to the 3' end of DNA strands in the telomere regions.

Telomerase plays a crucial role in DNA replication, particularly in maintaining the integrity and length of the telomeres. Telomeres are the protective caps at the ends of chromosomes, composed of repetitive sequences of non-coding DNA that protect the chromosome from degradation. During DNA replication, the enzymes that duplicate DNA cannot continue their duplication all the way to the end of chromosomes. If cells divided without telomeres, they would lose the ends of their chromosomes, and the necessary information they carry. This is where telomerase comes in.

Telomerase is a ribonucleoprotein that contains a protein component and an RNA component. The RNA component of telomerase serves as a template for the addition of new telomeric sequences to the ends of the chromosomes. The protein component of telomerase is a reverse transcriptase that carries out the synthesis of DNA from the RNA template. This process of adding telomeric sequences to the ends of chromosomes compensates for the natural shortening that occurs during DNA replication.

In most somatic (body) cells, telomerase activity is low or absent, leading to progressive shortening of telomeres with each cell division. This telomere shortening is associated with ageing and cellular senescence. However, in certain cells, such as germ cells, stem cells, and most cancer cells, telomerase activity is high, allowing these cells to maintain their telomere length and divide indefinitely.

In summary, telomerase is a vital enzyme in DNA replication, ensuring the preservation of genetic information and cellular health by maintaining the length of telomeres. Its activity varies among different cell types, with implications for ageing and cancer.