Final answer:
The ring-shaped protein complexes that bind to single-stranded DNA during replication to prevent reannealing are known as single-strand binding proteins (SSB). These along with helicase and topoisomerase are essential for DNA replication.
Step-by-step explanation:
The protein complexes that encircle one of the two single strands at the replication fork adjacent to the single-stranded:double-stranded junction are called single-strand binding proteins (SSB). These proteins play a crucial role during DNA replication. When the enzyme helicase unwinds the double helix, initiating replication, it creates tension by separating the two strands of DNA. This tension could potentially cause the strands to reanneal, or bond together again, which would interrupt the replication process.
To prevent this from happening, single-strand binding proteins bind to the single strands, stabilizing them and ensuring they remain separate. This allows DNA polymerases to read the templates and assemble the new strands. Furthermore, ahead of the replication fork, another enzyme known as topoisomerase works to manage the supercoiling of DNA, which helps to alleviate tension and prevent the DNA from becoming too tightly coiled. This whole process is vital to ensure that the DNA is accurately replicated, with each of the two resulting daughter molecules containing one old and one new DNA strand.