Question

The number of H bonds between guanine and cytosine is?
A. one
B. Two
C. Three
D. Four

Answer 1

Hint: A purine that includes adenine or guanine has a double ring. A pyrimidine that includes cytosine or thymine has a single ring. In DNA, a purine bonds with a pyrimidine. Depending on the structure, it will make two hydrogen bonds with each other or three.

Step by step answer:A base pair refers to two bases forming a "rung of the DNA ladder." A DNA nucleotide is formulated of a molecule of sugar, a molecule of phosphoric acid, and a molecule called a base. The bases refer to the "letters" that spell out the genetic code. In DNA, these code letters are A, T, G, and C, which are acronyms for the chemicals adenine, thymine, guanine, and cytosine, respectively. During base pairing, adenine always pairs with thymine, and guanine always pairs with cytosine. The number of H-bonds present between guanine and cytosine are three. In a DNA double helix, all types of nucleobase on one strand bond with just one type of nucleobase on the other strand. This is known as a complementary base pairing. The purines form hydrogen bonds with pyrimidines, in which adenine bonds only to thymine in two hydrogen bonds, and cytosine bonds only to the guanine in three hydrogen bonds. This arrangement of two nucleotides binding together across the double helix is known as a base pair. These hydrogen bonds are not covalent, therefore they can be broken and rejoined relatively easily.
So, the correct answer is option C- three

Note: Cytosine can form three hydrogen bonds with guanine, and adenine can form two hydrogen bonds with thymine. In simple words, C bonds with G and A bonds with T. This is called complementary base pairing because each base can only bond with a specific base partner.