OCR GCSE Biology Practice Exam 2026 – Comprehensive All-in-One Guide to Exam Success

The correct answer is the nitrogenous base. In a nucleotide, which serves as the building block of nucleic acids like DNA and RNA, the nitrogenous base is the component that varies among different nucleotides.

Nucleotides each consist of three parts: a five-sided sugar (ribose in RNA and deoxyribose in DNA), a phosphate group, and a nitrogenous base. The nitrogenous bases can be divided into two categories: purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil). The sequence and variety of these nitrogenous bases are crucial in determining the genetic information contained within nucleic acids. The specific arrangement of different nitrogenous bases in a strand of DNA or RNA encodes the information for producing proteins and regulating cell functions.

The five-sided sugar remains the same in all nucleotides that make up DNA (deoxyribose) and those that make up RNA (ribose), while the phosphate group is also consistent in structure across all nucleotides. Hydrogen bonds, which occur between nitrogenous bases during base pairing, are not a variable part of the nucleotide itself but rather a feature of the interactions between them when forming nucle