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Biology 2nd Baccalaureate

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2.4. Replication of DNA

DNA replication or duplication

DNA has to be duplicated in each cell cycle so that each daughter cell maintains the same genetic information as the cell it came from. This replication occurs during the interphase, before cell division, in order to be distributed among the daughter cells.

Mechanism of DNA replication

The replication of DNA begins with the breaking of the bonds by hydrogen bonds between bases nitrogeneadas of the pairs of complementary nucleotides, separating the two chains that form the DNA molecule.

As they are separated, each of the chains is used as a template to synthesize the complementary chain. Specific enzymes are responsible for adding nucleotides that are free whose nitrogenous bases are complementary to the template chain.

When the DNA molecule is open, with the two DNA strands separated, a so-called replication bubble forms.

In this way, two copies of DNA are obtained, each of the double helices having a chain from the initial DNA and another from newly created DNA. That is why DNA replication is said to be semi-conservative.

The two copies resulting from DNA replication or duplication are identical and therefore contain the same genetic information.

Each of these DNA double helices constitutes a sister chromatid to the duplicated chromosome.

The new nucleotides that are added have their nitrogen base complementary to the nucleotide of the chain that serves as a template. To avoid errors, there are repair enzymes that detect failures and replace the wrong nucleotides with the correct ones. If the repair mechanism is not working, a change has occurred in the DNA molecule, and that change is called a genetic mutation.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.