Does DNA Replicate Itself?!

0:00Have you ever wondered how your body knows how to grow, heal, or even exist from the moment you were just a handful of cells? It all starts with a process called DNA replication. Without it, you simply wouldn't be here. DNA replication begins with the enzyme topoisomerase, which unwinds the DNA by relieving tension in the helix.

0:28Next, helicase comes into action, separating the two strands by breaking the hydrogen bonds between the nitrogenous bases, forming a structure called the replication fork. Single-strand binding proteins, SSB for short, stabilize these separated strands to prevent them from reannealing and to protect them from degradation by nucleases.

0:54At the replication fork, primase synthesizes a short RNA fragment called a primer, which serves as a starting point for the synthesis of the new strand. DNA polymerase III needs the primer to begin adding complementary nucleotides to the template strand, always working in the 5' to 3' direction.

1:19On the leading strand, synthesis is continuous, since DNA polymerase III only requires one primer, but on the lagging strand it needs more than one, forming small fragments called Okazaki fragments. These fragments start with the RNA of the primers, which, since they contain uracil instead of thymine, must be replaced with DNA to ensure genetic fidelity.

1:47This task is carried out by DNA polymerase I, which removes the RNA primers and replaces them with DNA nucleotides. Finally, ligase joins the fragments to complete the strand continuously. The process continues until all the DNA has been copied, resulting in two identical molecules, each with one original strand and one new strand, a mechanism called semiconservative replication.