The molecule that completes the flow of information from DNA to protein is mRNA (messenger RNA).

Here's a breakdown of the flow:

1. DNA: Contains the genetic code for building proteins.

2. Transcription: DNA is transcribed into mRNA. This means the DNA sequence is copied into a complementary mRNA sequence.

3. mRNA: Carries the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm.

4. Translation: The mRNA sequence is translated into a chain of amino acids (a polypeptide), which then folds into a functional protein.

So, mRNA is the crucial intermediary that bridges the gap between DNA and protein synthesis.