Final answer:
If DNA's nitrogenous bases were linked by covalent bonds, DNA replication would be severely hindered because the bases would be difficult to separate, obstructing the necessary 'unzipping' process for template reading and new strand synthesis.
Step-by-step explanation:
If the nitrogenous bases in DNA were connected to each other by strong covalent bonds rather than hydrogen bonds, DNA replication would be significantly impeded. The enzyme designed to break the bonds between bases during DNA replication would be unable to do so if these bonds were covalent due to their strength. Consequently, the bases would not come apart easily, complicating the 'unzipping' process necessary for reading the sequence and forming a template for replication. Therefore, essential processes such as DNA polymerase adding nucleotides to a new strand using the original strand as a template would be obstructed.