Final answer:
In DNA replication, helicase separates the strands of the double helix, allowing DNA polymerase to synthesize a new complementary strand in the 5' to 3' direction. Primase and PCNA assist in the process, with DNA ligase sealing the nicks between Okazaki fragments on the lagging strand.
Step-by-step explanation:
Understanding DNA Replication
The process of DNA replication is intricate and involves several key enzymes, including helicase and DNA polymerase. Helicase plays a critical role by unwinding the DNA double helix at the origin of replication. This enzyme breaks the hydrogen bonds between the base pairs, allowing the two strands to separate and form a replication fork. Concurrently, topoisomerase works to relieve the tension caused by the unwinding process, and single-stranded binding proteins stabilize the unwound strands.
Once the strands are separated, primase synthesizes a short RNA primer necessary for DNA polymerase to begin synthesizing a new, complementary strand. It is important to note that DNA replication occurs in the 5' to 3' direction. DNA polymerase III in prokaryotes, or DNA polymerases δ and ε in eukaryotes, extend the new strand by adding nucleotides complementary to the template strand. As replication proceeds, a sliding clamp protein, PCNA, helps stabilize the DNA polymerase on the DNA template.
On the leading strand, replication is continuous, whereas on the lagging strand, DNA is synthesized in short, discontinuous segments known as Okazaki fragments. An RNA primer initiates each of these fragments. Once the primer is removed by RNase H and replaced by DNA nucleotides, DNA ligase seals the nicks, forming a continuous strand. In eukaryotic cells, special attention is needed during telomere replication at the ends of the chromosomes to prevent the loss of genetic information over time.