DNA contains genetic information that determines how a polypeptide is made. However, DNA is found in the nucleus while polypeptides are made at the ribosome which is found in the cytoplasm.
DNA is a very large molecule that cannot pass through the nuclear pores on the nucleus. Therefore, polypeptide synthesis involves a 2-step process
1. Transcription - The template strand of the gene is used to make a complementary and smaller molecule known as the mRNA. mRNA will then leave the nucleus and bind to the ribosomes for polypeptide synthesis.
2. Translation - Sequence of mRNA codons are read and used to code for specific sequence of amino acids on a polypeptide chain.