What are the differences between leading and lagging strands in DNA replication?

The leading strand in DNA replication is synthesised continuously, while the lagging strand is synthesised discontinuously in fragments.

In DNA replication, the two original DNA strands are separated and each serves as a template for the synthesis of a new, complementary strand. This process is carried out by an enzyme called DNA polymerase. However, due to the antiparallel nature of DNA, the two new strands are synthesised in different ways.

The leading strand is synthesised in the same direction as the replication fork, which is the point where the two original strands are being separated. This allows the DNA polymerase to add nucleotides continuously to the 3' end of the new strand as it moves along the template. The synthesis of the leading strand is therefore a relatively straightforward and efficient process.

On the other hand, the lagging strand is synthesised in the opposite direction to the replication fork. This means that DNA polymerase cannot add nucleotides continuously as it does on the leading strand. Instead, it has to wait until a sufficient section of the template has been exposed, then it moves backwards along the template, synthesising a short fragment of the new strand. These fragments, known as Okazaki fragments, are later joined together by another enzyme called DNA ligase to form the complete strand.

The synthesis of the lagging strand is therefore a more complex and slower process than that of the leading strand. It also requires more enzymes and other proteins to ensure that the fragments are synthesised correctly and joined together in the right order.

In summary, the main difference between the leading and lagging strands in DNA replication is the way in which they are synthesised. The leading strand is synthesised continuously in the same direction as the replication fork, while the lagging strand is synthesised discontinuously in the opposite direction, in the form of Okazaki fragments. This difference arises from the antiparallel nature of DNA and the directionality of the DNA polymerase enzyme.