Number of Hydrogen Bonds in a Guanine-Cytosine Base Pair

Introduction:
In DNA, the four nucleotide bases adenine (A), thymine (T), cytosine (C), and guanine (G) form complementary base pairs. Guanine (G) always pairs with cytosine (C), and adenine (A) always pairs with thymine (T). These base pairs are held together by hydrogen bonds, which are weak chemical bonds formed between hydrogen atoms and electronegative atoms.

Guanine-Cytosine Base Pair:
When guanine (G) and cytosine (C) come together to form a base pair in DNA, several hydrogen bonds are formed between them. Let's explore the structure of the guanine-cytosine base pair and the hydrogen bonds involved.

Structure of Guanine-Cytosine Base Pair:
1. Guanine (G) and cytosine (C) are complementary bases, meaning they have specific shapes that allow them to fit together perfectly.
2. The guanine molecule has a planar structure with several functional groups, including an amino group (-NH2) and a carbonyl group (-C=O).
3. The cytosine molecule also has a planar structure with functional groups, including an amino group (-NH2) and a carbonyl group (-C=O).
4. When G and C come together, the amino group of cytosine forms hydrogen bonds with the carbonyl group of guanine, and vice versa.
5. Specifically, three hydrogen bonds are formed between guanine and cytosine: two hydrogen bonds between the amino group of cytosine and the carbonyl group of guanine, and one hydrogen bond between the amino group of guanine and the carbonyl group of cytosine.

Conclusion:
Therefore, the correct answer is '3,3', indicating that there are three hydrogen bonds present in a guanine-cytosine base pair. The specificity and strength of these hydrogen bonds contribute to the stability and integrity of the DNA double helix.