#biologyanimation #telomere #replication #telomerase
Telomere Replication in Eukaryotes:
• As we have already discussed DNA replication in earlier videos that how DNA synthesis begins at origins of replication and continues until the replication machinery reaches the end of chromosome.
• But the problem arises when replication fork reaches the end of chromosome. So in this video, we will deal with the end replication of eukaryotic chromosomes which occurs by a special mechanism
• The leading strand is its entirety. But the ends of lagging strand can’t be completed; because once the final RNA primer has been removed there is no way to replace it with DNA.
• These gaps at the end of the lagging strand must be filled in by a special mechanism to prevent the chromosome ends from shrinking with each round of cell division.
• For this, as Eukaryotes have long repetitive nucleotide sequences at the end of their chromosomes which is termed as telomeres.
• These telomeric DNA sequences contain a G-rich series of repeats which is recognized by the enzyme called telomerase to the chromosome ends which binds on it.
• And as the telomerase carries a short piece of RNA sequence of itself, complementary to the DNA repeat sequence, acts as template for telomere DNA synthesis.
• Telomerase binds and elongates the ends of the parental strand by adding more copies of repeated sequences in 5’ to 3’ direction as it moves down the parental strand. This is termed as RNA-templated DNA synthesis which occurs via reverse transcription mechanism.
• After that completion of lagging strand is done by DNA polymerase alpha (DNA-templated DNA synthesis) which have DNA primase as one of its subunits by using these extensions as a template.
• In this way, telomeric replication occurs to prevent linear eukaryotic chromosomes from shortening with each cell division.
Music: Ben Sound
