Biochemical classification: Adenosine triphosphate (ATP) belongs to which major class of biomolecules?

Introduction / Context:
ATP is the central energy currency of the cell and also a precursor for RNA synthesis. Correctly classifying ATP helps connect energy metabolism, nucleic acid biochemistry, and cell signaling.

Given Data / Assumptions:

• ATP is composed of adenine (a nitrogenous base), ribose (a pentose sugar), and three phosphate groups.
• Nucleotides are base + sugar + phosphate; nucleosides lack phosphate.
• High-energy phosphoanhydride bonds store transferable free energy.

Concept / Approach:
Because ATP contains base, sugar, and phosphate, it is a nucleotide. When incorporated into RNA, ATP appears as AMP within the polymer. The triphosphate form functions in metabolism as a phosphoryl-group donor and in signaling (e.g., cAMP derived from ATP).

Step-by-Step Solution:
Identify structural components: adenine + ribose + triphosphate. Map structure to definition: nucleotide = base + sugar + phosphate. Select the option “Nucleotide.”

Verification / Alternative check:
Biochemistry texts universally classify ATP as a ribonucleotide triphosphate, one of the four immediate precursors for RNA synthesis (ATP, GTP, CTP, UTP).

Why Other Options Are Wrong:

• Fatty acid / Steroid / Disaccharide: Lipids or carbohydrates, lacking the nucleotide triad.
• Amino acid: Protein building blocks, not nucleotides.

Common Pitfalls:
Confusing nucleoside (adenosine) with nucleotide (adenosine monophosphate or triphosphate). The presence of phosphate distinguishes the nucleotide.

Final Answer:
Nucleotide.