what direction along a DNA strand does DNA polymerase add base pairs
DNA polymerase adds base pairs in the 5' to 3' direction along a DNA strand. To understand why this is the case, let's take a closer look at the structure of DNA.
DNA is made up of two strands that are complementary to each other, with each strand running in opposite directions. One strand is referred to as the leading strand, while the other is known as the lagging strand.
The leading strand is synthesized continuously in the 5' to 3' direction, meaning that the DNA polymerase can add new nucleotides in a continuous manner. On the other hand, the lagging strand is synthesized discontinuously in short fragments known as Okazaki fragments. These fragments are then later joined together to form a continuous strand.
The synthesis of new DNA strands by DNA polymerase involves complementary base pairing. Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). As DNA polymerase moves along the template strand, it reads the existing bases and adds new complementary nucleotides to the growing strand.
Importantly, DNA polymerase can only add new nucleotides to the 3' end of an existing strand. The 3' end of a DNA strand has a free hydroxyl (-OH) group attached to the 3' carbon of the sugar molecule, which is necessary for the formation of the phosphodiester bond that links nucleotides together.
Therefore, DNA polymerase moves in the 5' to 3' direction along the template strand because it can only add new nucleotides to the 3' end of the growing DNA strand. This directionality ensures the accurate replication of the DNA molecule during cell division.