Final answer:
Hydrogen bonds and van der Waals interactions are necessary because they maintain the proper structure and functionality of DNA and proteins, which are crucial for DNA replication, transcription, and enzyme substrate binding.
Step-by-step explanation:
Hydrogen bonds and van der Waals interactions are necessary for cells because they play critical roles in the stabilization and function of biomolecules. These weak associations between molecules are essential for maintaining the proper structure and function of DNA and proteins. For instance, hydrogen bonds between functional groups within the same molecule or different molecules help macromolecules to fold into and maintain their proper shape, which is crucial for their functionality. This involves important processes such as DNA complementary base pairing, which is fundamental to DNA replication and transcription, and the binding of enzymes to their substrates. Similarly, van der Waals interactions, reliant on slight fluctuations in electron densities, also contribute to the three-dimensional structure of proteins required for their correct operation within cells.