Here's a problem to solve: A scientist uses a special chemical marker to label some amino acids. He follows the marker until it becomes part of a large molecule in a cell. Which molecule does he find the chemical marker on?

Among the 4 following options, which is the correct answer?

- A: a lipid in a membrane
 
- B: an enzyme in a lysosome
 
- C: a polysaccharide in a cell wall
 
- D: a DNA molecule in a mitochondrion
 