Question

The number of hydrogen bond(s) present in a guanine-cytosine base pair is .............

Hint:

In DNA base pairing, guanine and cytosine form three hydrogen bonds, making them stronger than adenine-thymine pairs, which form only two hydrogen bonds.

Answer 1

Correct Answer: 3

Step 1: Understanding the guanine-cytosine base pair. 
Guanine and cytosine pair through three hydrogen bonds in the DNA double helix. The base pairing follows specific hydrogen bond rules: guanine forms hydrogen bonds with cytosine through two NH groups and one oxygen atom. 
 

Step 2: Analyzing the number of hydrogen bonds. 
Each hydrogen bond is formed as follows: 

- One hydrogen bond between the NH group of guanine and the carbonyl oxygen of cytosine. 

- Another hydrogen bond between the amino group of guanine and the N-H group of cytosine. 

- The third hydrogen bond is formed between the N-H group of guanine and the N atom of cytosine. 
 

Step 3: Conclusion. 
The guanine-cytosine base pair contains 3 hydrogen bonds.