Final answer:
The activated form of D-ribose-5-phosphate is the starting molecule in the de novo purine synthesis pathway, which is integral for creating the building blocks of nucleic acids.
Step-by-step explanation:
The molecule utilized at the start of the purine synthesis pathway is the activated form of D-ribose-5-phosphate which serves as the initial scaffold for the attachment of the purine ring. De novo purine synthesis involves the step-by-step construction of the purine ring structure using precursors like aspartate, glutamine, formate, glycine, and respiratory carbon dioxide. The importance of this pathway lies in the biosynthesis of purine nucleotides, which are essential components of nucleic acids such as DNA and RNA.