Question

during DNA replication, they separate double-stranded DNA into single strands allowing each strand to be copied

Answer 1

During DNA replication, the double-stranded DNA unwinds and separates into two single strands. This process is facilitated by enzymes known as **helicases**, which break the hydrogen bonds between the base pairs, resulting in the formation of a replication fork. Each single strand serves as a template for the synthesis of a new complementary strand.

**Key steps in DNA replication include:**

1. **Unwinding the DNA:** Helicases unwind the double helix, separating the two strands.

2. **Stabilization of single strands:** Single-strand binding proteins (SSBs) bind to the separated strands to prevent them from re-annealing or forming secondary structures.

3. **Priming the strands:** The enzyme **primase** synthesizes short RNA primers on each template strand. These primers provide a starting point for DNA synthesis because DNA polymerases require a primer with a free 3' hydroxyl (OH) group.

4. **DNA synthesis:** DNA polymerase extends the RNA primers by adding complementary nucleotides to the growing DNA strand, synthesizing new DNA in a 5’ to 3’ direction. The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments known as **Okazaki fragments.**

5. **Removal of RNA primers:** The RNA primers are removed, and the gaps are filled with DNA nucleotides.

6. **Ligation:** The enzyme **DNA ligase** seals the gaps between the Okazaki fragments on the lagging strand, creating a continuous DNA strand.

At the end of replication, two identical double-stranded DNA molecules are produced, each containing one original (template) strand and one newly synthesized strand, a process known as **semiconservative replication**.