Complex sentence: Telomeres are extended by telomerases, part of a protein subgroup of specialized reverse transcriptase enzymes known as TERT (TElomerase Reverse Transcriptases) that are involved in synthesis of telomeres in humans and many other, but not all, organisms.
Split into simpler sentences: Telomeres are extended by telomerases, part of a protein subgroup of specialized reverse transcriptase enzymes known as TERT (TElomerase Reverse Transcriptases). Telomerases are involved in synthesis of telomeres in humans and many other, but not all, organisms.