Biomolecules — Classification: ATP belongs to which general molecular category?

Introduction / Context:
Adenosine triphosphate (ATP) is the universal energy currency in cells. Knowing its chemical class clarifies how it is synthesized, hydrolyzed, and used in metabolism and signaling.

Given Data / Assumptions:

• ATP contains adenine, ribose, and three phosphate groups.
• It participates in kinase reactions and drives many endergonic processes.
• We must select the correct molecular class.

Concept / Approach:
ATP is a nucleotide triphosphate: a nitrogenous base (adenine) linked to a pentose sugar (ribose) and a chain of three phosphates. Hydrolysis of the phosphoanhydride bonds releases free energy. It is not a polysaccharide, protein, or a single amino acid.

Step-by-Step Solution:

Verification / Alternative check:
Biochemistry texts classify ATP as a ribonucleoside triphosphate (rNTP), confirming the selection.

Why Other Options Are Wrong:

• Polysaccharides are long carbohydrate chains (e.g., glycogen, starch), not ATP.
• Proteins are polypeptides; ATP is not polypeptidic.
• Amino acids are basic building blocks of proteins, not energy nucleotides.

Common Pitfalls:
Confusing “nucleoside” (adenosine) with “nucleotide” (adenosine plus phosphate group(s)). ATP is a nucleotide.

Final Answer:
Nucleotides