O Processo de Replicação do DNA - (Animação Narrada em 3D)
Replication of DNA: Understanding the Process
Structure of DNA
- DNA is a molecule composed of two strands twisted into a double helix, with each strand made up of a sequence of four chemical bases represented by the letters A, C, G, and T.
- The strands are complementary; for every occurrence of T in one strand, there is an obligatory A in the opposite strand. Similarly, C pairs with G.
Directionality and Replication Initiation
- Each DNA strand has a 5' end and a 3' end, which determine the direction of replication. New strands are synthesized from 5' to 3'.
- The first step in DNA replication involves separating the two strands using an enzyme called helicase, creating what is known as the replication fork.
Role of Primers and Polymerases
- An enzyme called primase synthesizes a short RNA segment known as a primer that marks the starting point for new DNA synthesis.
- The enzyme DNA polymerase attaches to this primer to begin constructing the new DNA strand continuously in the 5' to 3' direction.
Lagging Strand Synthesis
- The other strand (lagging strand) cannot be synthesized continuously due to its opposite orientation; it is formed in small segments called Okazaki fragments.
- Each Okazaki fragment starts with its own RNA primer, allowing short stretches of DNA to be added before another primer is formed further along.
Completion and Finalization
- Once replication is complete, an enzyme called exonuclease removes all RNA primers from both strands.