Final answer:
DNA is the molecule that holds instructions for the synthesis of proteins and copies itself before cell division.
Step-by-step explanation:
The molecule that holds instructions for the synthesis of proteins and copies itself before cell division is DNA (deoxyribonucleic acid).
DNA stores the information necessary for instructing the cell to perform all of its functions. Cells use the genetic code stored within DNA to build proteins, which ultimately determine the structure and function of the cell. To make proteins, DNA is transcribed into a molecule called mRNA (messenger RNA), which then carries the instructions to the ribosome where protein synthesis occurs.