Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of

Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of . Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of . guanines is always the same as thymines pyrimidines is always larger than purines cytosines is always the same as adenines purines is always larger than the number of pyrimidines purines is always the same as pyrimidines

The Correct Answer and Explanation is :

Watson and Crick were aware of the following key point regarding the number of bases in DNA when they were trying to determine its structure: the number of guanines is always the same as the number of cytosines (G=C) and the number of adenines is always the same as the number of thymines (A=T).

Explanation

During their research in the early 1950s, Watson and Crick built upon existing knowledge about DNA and its components. One of the pivotal pieces of evidence they utilized was Chargaff’s rules, formulated by biochemist Erwin Chargaff. Chargaff discovered that in the DNA of various organisms, the amount of adenine (A) always equaled the amount of thymine (T), and the amount of guanine (G) always equaled the amount of cytosine (C). This observation suggested a pairing mechanism that was crucial for understanding how DNA replicates and encodes genetic information.

These base-pairing rules provided a foundational understanding of how the two strands of the DNA double helix are held together through specific interactions: adenine pairs with thymine through two hydrogen bonds, while guanine pairs with cytosine through three hydrogen bonds. This pairing is essential for the stability of the DNA molecule and ensures accurate replication during cell division.

Watson and Crick used this information alongside X-ray diffraction data, particularly from Rosalind Franklin, which indicated a helical structure. They proposed the double-helix model of DNA in 1953, which effectively explained how genetic information is stored and passed on. Thus, the knowledge of base pairing (G=C and A=T) was critical to their understanding of DNA’s structure, enabling them to create a model that accurately represented how genetic material is organized within cells.

This discovery not only elucidated the physical structure of DNA but also laid the groundwork for the fields of molecular biology and genetics, revolutionizing our understanding of heredity and the molecular basis of life.