OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What type of bond connects the base pairs in DNA?

Covalent bonds
Hydrogen bonds
Ionic bonds
Peptide bonds

The correct answer is: Hydrogen bonds

In DNA, the base pairs are connected by hydrogen bonds, which play a crucial role in maintaining the structure of the DNA double helix. Each base pair consists of two nitrogenous bases (adenine with thymine, and guanine with cytosine) that are held together by these specific hydrogen bonds. The relatively weak nature of hydrogen bonds allows for the DNA strands to separate during processes such as DNA replication and transcription, which is essential for genetic functions. Covalent bonds, on the other hand, are responsible for linking the phosphate and sugar components of the DNA backbone, providing structural integrity to the overall molecule. Ionic bonds do not participate in the base pairing of DNA. Likewise, peptide bonds are pertinent in protein synthesis, connecting amino acids rather than base pairs in nucleic acids. Understanding the types of bonds and their roles helps clarify how the DNA molecules function and how genetic information is safely stored and accessed within living organisms.