The central dogma of molecular biology is that protein synthesis is a unidirectional process. The first step of protein synthesis is DNA replication in which the DNA double helix serves as a template for the replication of a second, complementary strand. Next, transcription of this complementary DNA strand involves synthesizing mRNA within the nucleus. The next step, translation, converts this mRNA into protein within the cytoplasm. Splicing is the posttranscriptional modification of RNA that results in the removal of introns and joining of exons.