In DNA bases, CG is one pair and AT is another pair because the double ring bonds with the single ring. Why can't Guanine bond with Thymine?
Guanine (G) and Thymine (T) cannot form a base pair in DNA because they do not have compatible chemical structures and bonding patterns. The structure of DNA is based on complementary base pairing, where adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). This is known as Chargaff's rule.
The reason for this pairing specificity lies in the hydrogen bonding patterns that occur between the bases. Adenine and thymine can form two hydrogen bonds with each other, while guanine and cytosine can form three hydrogen bonds. These hydrogen bonds provide stability to the DNA structure.
Guanine and thymine have different chemical structures. Guanine has a double-ring structure called a purine, while thymine has a single-ring structure called a pyrimidine. These structural differences make it energetically unfavorable for guanine to bond with thymine because their bonding patterns do not match. Guanine prefers to form three hydrogen bonds with cytosine, as it complements the three hydrogen bonding sites on cytosine.
In summary, the specific pairing of adenine with thymine and cytosine with guanine in DNA is determined by their complementary structures and the ability to form the appropriate number of hydrogen bonds, which ensures the stability of the DNA molecule.