DNA replication - 3D

DNA (Deoxyribonucleic Acid) is composed of two strands twisted around each other to form a double helix.
Each strand consists of a sequence of four chemical bases:
- A (Adenine)
- C (Cytosine)
- G (Guanine)
- T (Thymine)
The two strands are complementary, meaning:
- An A on one strand pairs with a T on the opposite strand.
- A C on one strand pairs with a G on the opposite strand.
Each strand has a 5' end and a 3' end, running in opposite directions.

The first step involves separating the two strands, a process called unzipping, carried out by the enzyme helicase, creating a replication fork.
Each separated strand serves as a template for creating a new DNA strand.
Primase synthesizes a small RNA primer to mark the starting point for new strand construction.

DNA polymerase binds to the primer and initiates the formation of the new strand.
DNA polymerase can only add bases in the 5' to 3' direction.
- The leading strand is synthesized continuously in the 5' to 3' direction.
- The lagging strand, running in the opposite direction, is synthesized discontinuously in Okazaki fragments:
  - Each Okazaki fragment begins with an RNA primer.
  - DNA polymerase adds DNA bases in a 5' to 3' direction for each fragment.
  - Additional primers are placed further down the lagging strand for each new fragment.

After synthesizing new DNA strands, the enzyme exonuclease removes all RNA primers from both strands.
A second DNA polymerase fills in the gaps left by the removed primers with DNA bases.
The final step involves DNA ligase, which connects the fragments of DNA, resulting in a continuous double-stranded molecule.

DNA replication is semi-conservative, as each resulting DNA molecule consists of one old (conserved) strand and one newly synthesized strand.