Questions: Which molecule is often called the cell's energy currency? Flavin adenine dinucleotide Adenosine triphosphate Nicotinamide adenine dinucleotide phosphate Nicotinamide adenine dinucleotide

The answer is the second one: Adenosine triphosphate.

Explanation for each option:

1. Flavin adenine dinucleotide (FAD): This molecule is a redox cofactor involved in several important reactions in metabolism. It is not primarily known as the cell's energy currency.

2. Adenosine triphosphate (ATP): This molecule is often referred to as the cell's energy currency because it stores and transfers energy within cells. It is used to power various cellular processes.

3. Nicotinamide adenine dinucleotide phosphate (NADP+): This molecule is involved in anabolic reactions, such as lipid and nucleic acid synthesis, but it is not primarily known as the cell's energy currency.

4. Nicotinamide adenine dinucleotide (NAD+): This molecule is a coenzyme found in all living cells and is involved in redox reactions, carrying electrons from one reaction to another. However, it is not primarily known as the cell's energy currency.

In summary, Adenosine triphosphate (ATP) is the correct answer as it is widely recognized as the cell's energy currency.