In molecular biology, each nucleotide in DNA or RNA is built from three basic parts. Which combination correctly describes these three fundamental components of a nucleotide?

Introduction / Context:
Nucleotides are the building blocks of nucleic acids, namely DNA and RNA. Understanding their structure is fundamental for topics such as DNA replication, transcription, and translation. Each nucleotide has three distinct parts that together allow nucleic acids to store genetic information and form long chains. This question asks you to identify the correct combination of these three basic components from several possibilities that mix different types of biomolecules.

Given Data / Assumptions:

• The focus is on the structure of a nucleotide, not a complete nucleic acid strand.
• Options combine items such as nitrogenous bases, sugars, phosphate groups, fatty acids, glycerol, amino acids, and specific bases.
• We assume standard structures for nucleotides in DNA and RNA.
• We also assume familiarity with the four major groups of biomolecules: carbohydrates, lipids, proteins, and nucleic acids.

Concept / Approach:
A nucleotide consists of three fundamental components: a nitrogenous base, a pentose sugar, and a phosphate group. The nitrogenous base can be a purine (adenine or guanine) or a pyrimidine (cytosine, thymine, or uracil). The pentose sugar is deoxyribose in DNA and ribose in RNA. One or more phosphate groups are attached to the sugar, forming nucleotides like AMP, ADP, or ATP. Fatty acids and glycerol are parts of lipids, not nucleotides. Amino acids are the building blocks of proteins. A particular set of bases such as adenine, guanine, and thymine represent examples of nitrogenous bases but do not by themselves form the three-part structure of a nucleotide.

Step-by-Step Solution:
Step 1: Recall the textbook definition: a nucleotide is composed of a nitrogenous base, a pentose sugar, and a phosphate group. Step 2: Examine option A and see that it lists nitrogenous base, pentose sugar, and phosphate group, which matches the definition exactly. Step 3: Consider option B, which introduces fatty acid and glycerol, components of lipids, not nucleotides. Step 4: Look at option C, which includes amino acid, a building block of proteins, not part of a nucleotide structure. Step 5: Evaluate option D, which places glycerol and triglyceride, again related to fats rather than nucleic acids. Step 6: Notice that option E lists only specific nitrogenous bases without including sugar and phosphate, so it does not describe the complete three-part nucleotide unit. Step 7: Conclude that option A is the only one that correctly states all three fundamental components.

Verification / Alternative check:
Diagrams of DNA and RNA in textbooks show a sugar-phosphate backbone with nitrogenous bases projecting from the sugar. Each repeating unit of the chain is a nucleotide. The sugar is either ribose or deoxyribose, the phosphate forms part of the backbone, and the base carries the genetic information. Chemical formulas for nucleotides such as adenosine triphosphate (ATP) also clearly display an adenine base, a ribose sugar, and three phosphate groups. No standard representation of nucleotides uses fatty acids, glycerol, or amino acids as structural components, confirming that the correct combination is base, sugar, and phosphate.

Why Other Options Are Wrong:
Option B: Nitrogenous base, fatty acid, and glycerol mixes one correct component (base) with two typical lipid components, not nucleotide parts. Option C: Pentose sugar, amino acid, and phosphate group again combines one correct piece (sugar and phosphate) with an amino acid, which belongs to proteins. Option D: Phosphate group, glycerol, and triglyceride is strongly associated with lipid chemistry and has no direct relation to nucleotide structure. Option E: Adenine, guanine, and thymine are examples of nitrogenous bases only, and do not describe the three-part composition of a nucleotide.

Common Pitfalls:
A common mistake is to confuse the different biomolecule groups and think that any combination of familiar names might be correct. Learners may also think that listing several bases counts as a full nucleotide. To avoid this, remember that nucleotides always combine three specific types of components: a base for information, a pentose sugar as the core, and one or more phosphate groups for linkage and energy transfer. Lipid components like fatty acids and glycerol, and protein components like amino acids, belong to separate biomolecule categories and should not be mixed into nucleotide definitions.

Final Answer:
Each nucleotide in DNA or RNA is made up of three basic parts: a nitrogenous base, a pentose sugar, and a phosphate group.