Final answer:
Gregor Mendel's work did not directly contribute to the discovery of the DNA structure. Linus Pauling, Erwin Chargaff, and Rosalind Franklin's efforts laid important groundwork that led to the DNA double helix model formulated by James Watson and Francis Crick.
Step-by-step explanation:
The scientist whose work did not contribute to the discovery of the structure of the DNA molecule is Gregor Mendel. While Gregor Mendel is known as the father of genetics for his pioneering work on inheritance patterns in pea plants, his research did not directly contribute to the understanding of the DNA structure. The other scientists listed: Linus Pauling, Erwin Chargaff, and Rosalind Franklin, all provided crucial insights that led to the determination of the DNA's double helix structure by James Watson and Francis Crick. Linus Pauling proposed a structural model of DNA and discovered the secondary structure of proteins. Erwin Chargaff formulated rules indicating that DNA bases are paired in a certain way, and Rosalind Franklin's X-ray diffraction images were instrumental in revealing the double helix shape of DNA.