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QuestionBiochemistry

"ATP is NOT a nucleoside because it ________. A. Has three phosphates instead of just one B. Lacks the deoxyribosyl group C. Has phosphate groups D. Is not connected to a carbohydrate group"
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Answer

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Step 1:
Let's solve this step by step:

Step 2:
: Understand the definition of a nucleoside

- A nucleoside is a molecule composed of a nucleic base (like adenine, guanine, cytosine, or thymine) attached to a sugar molecule (ribose or deoxyribose) - Specifically, a nucleoside consists of:

Step 3:

A nitrogenous base

Step 4:

A sugar molecule (ribose or deoxyribose)

Step 5:
: Analyze the structure of ATP (Adenosine Triphosphate)

- ATP contains:

Step 6:

Adenine (the base)

Step 7:

Ribose (the sugar)

Step 8:

THREE phosphate groups

Step 9:
: Identify the key difference between ATP and a typical nucleoside

- A nucleoside has NO phosphate groups - ATP has THREE phosphate groups attached to the ribose sugar - This means ATP is actually a nucleotide, not a nucleoside

Step 10:
: Evaluate the answer choices

- Choice A is correct: ATP has three phosphates instead of the zero phosphates found in a nucleoside

Final Answer

ATP is NOT a nucleoside because it has three phosphates instead of just one. Key Insight: The distinction between nucleosides (base + sugar) and nucleotides (base + sugar + phosphate group(s)) is crucial in biochemistry.