Question

What would happen to the replication process if the growing DNA chain did not have a free 3 ' end?

Short answer

Without a free 3' end, DNA replication cannot proceed because DNA polymerase cannot add new nucleotides.

Step-by-step solution

Understand DNA Replication

In DNA replication, an enzyme called DNA polymerase adds nucleotides to a growing DNA strand. The growth of this new DNA strand occurs in the 5' to 3' direction, requiring a free 3' hydroxyl group (-OH).

Role of the 3' End

The free 3' end of the DNA strand provides a hydroxyl group that is crucial for forming phosphodiester bonds with incoming nucleotides.

Effect of No Free 3' End

If the growing DNA chain did not have a free 3' end, the DNA polymerase would not be able to add new nucleotides. This would halt the replication process.

Conclusion

The replication process depends on the presence of a free 3' end to continue adding nucleotides to the growing chain. Without it, replication stops.

Key concepts

DNA polymerase

DNA polymerase is a crucial enzyme in the process of DNA replication. It’s responsible for adding nucleotides, which are the building blocks of DNA, to a growing DNA strand. DNA polymerase ensures that the DNA strands are copied accurately, ensuring the genetic information is retained from one generation to the next. During DNA replication, DNA polymerase reads the template strand and adds complementary nucleotides to the new DNA strand being formed. This enzyme is incredibly precise, but errors can sometimes occur. Fortunately, DNA polymerase also has proofreading abilities to correct these mistakes and maintain the integrity of the genetic code.

5' to 3' direction

One of the key principles of DNA replication is that DNA polymerase can only add nucleotides in a specific direction, known as the '5' to 3' direction. This means that the new DNA strand grows by adding nucleotides to the 3' end. The numbers refer to the carbon atoms in the sugar component of the DNA backbone. The 5' end has a phosphate group attached, while the 3' end has a hydroxyl group (-OH). Replication proceeds by extending the chain at the 3' end, making the 3' hydroxyl group crucial. Each nucleotide added provides a new 3' hydroxyl group, allowing the next nucleotide to attach, continuing the chain.

phosphodiester bonds

Phosphodiester bonds are the chemical bonds that hold together the backbone of DNA strands. They form between the phosphate group of one nucleotide and the 3' hydroxyl group of the sugar of another nucleotide. DNA polymerase facilitates the creation of these bonds during DNA replication. As new nucleotides are added to the growing DNA strand, phosphodiester bonds ensure the stability and integrity of the DNA molecule. In other words, without phosphodiester bonds, the DNA strand could not hold together, and the replication process could not proceed efficiently.

3' hydroxyl group

The 3' hydroxyl group (-OH) is essential for DNA replication. It is found at the 3' end of the growing DNA strand and is critical because it enables the addition of new nucleotides. DNA polymerase requires this free 3' hydroxyl group to form the phosphodiester bond with the incoming nucleotide. Without a free 3' end, the enzyme cannot attach new nucleotides, effectively halting the DNA replication process. Thus, the availability of the 3' hydroxyl group at the end of a DNA strand is a key factor in the continuation of DNA synthesis.