why does a new dna strand elongate only in the 5′ to 3′ direction during dna replication?
During DNA replication, a new DNA strand elongates only in the 5′ to 3′ direction because of the way in which DNA polymerase, the enzyme responsible for synthesizing the new strand, functions.
DNA polymerase adds deoxyribonucleotides (the building blocks of DNA) to the template strand in a specific order determined by the base pairing rules (A with T, and C with G). It can only add new nucleotides to the 3′ end of an existing chain and cannot remove nucleotides once they have been added.
As a result, the new DNA strand elongates in the 5′ to 3′ direction, with the 5′ end representing the starting point and the 3′ end representing the growing end. This process is called 5′ to 3′ synthesis.
In summary, DNA polymerase synthesizes new DNA strands in the 5′ to 3′ direction because it can only add new nucleotides to the 3′ end of an existing chain and cannot remove nucleotides once they have been added. This process is essential for the accurate and efficient synthesis of new DNA strands during replication.
all fine except that for example
both the phage T4 DNA polymerase and E. coli DNA Pol III holoenzyme have 3’→5′ exonuclease activity important for proofreading.
Thank you