system
Given the following post, respond as if you're commenting on Reddit:
human
Is it true that human cells lose 100 base pairs from the ends of chromosome after each replication?

Is it true that human cells lose 100 base pairs from the ends of chromosome after each replication? Does that mean that as we age we loose more and more genetic information?
gpt
So, lets talk about the end of replication problem and how it's solved in eukaryotes like us humans.

DNA replication requires the use of RNA primers that prime new synthesis of DNA since DNA synthesis can only occur in what we call a 5' to 3' direction (in reference to the 'directionality' of the molecule). These RNA primers are complimentary and, in the case of RNA primers in the middle of the chromosome, are simply cut out and filled in with bonafide DNA instead of RNA. This filling in can occur because new DNA synthesis has filled in to the RNA Primer 5' of it, so the new DNA can be used as the 'primer for the primer'. 

In the case of the ends of chromosomes, there's no upstream 5' DNA to act as a primer, so when that RNA primer is removed, a little bit of DNA is lost! This doesn't happen in prokaryotes due to their circular genomes but with eukaryotes this is a big problem! The solution that we employ is to add tandem repeats of 6 nucleotides to the end of the chromosomes that can be replaced by an ribonucleoprotein (that is, a protein that contains RNA) called telomerase. When telomerase is active, it allows cells to replenish telomeric repeats, but when it's not around, DNA replication will slowly eat away the DNA about 20-40 bases per replication. In the case where telomerase isin't active, such as a dish of cultured cells or many of the somatic cells in your body, they can only replicate 30-60 times (Called the Hayflick limit) before entering a phase called crisis where they are no longer capable of dividing. 

So what relevance do telomeres have to present science? Well, there's evidence that much of aging may be attributed to telomeres, and about 85% of malignant tumors have mutations that allow for the upregulation of telomerase making it an interesting target for anti-cancer medications. 

So yes, we lose DNA every replication, but most of the time the DNA is non essential DNA in the form of telomeric repeats.