the central dogma
/ SEN-trul DOG-muh /
Imagine a master cookbook locked in a library that no one is allowed to take home. To actually cook, you hand-copy one recipe onto a scrap of paper, carry the scrap to the kitchen, and follow it. The locked cookbook is your DNA, the disposable copy is RNA, and the finished dish is a protein. The central dogma is simply the name for that one-way flow of instructions: DNA is read into RNA, and RNA is read into protein.
Stated precisely, the central dogma describes how the sequence of building blocks in your genes gets turned into the sequence of building blocks in proteins, which do most of the actual work in a cell. The flow has two main steps. First, transcription copies a stretch of DNA into a strand of RNA. Second, translation reads that RNA, three letters at a time, to string together amino acids into a protein. The key claim is about direction: once information has passed into a protein, it does not flow back out of the protein into nucleic acids.
It is worth being honest about what the dogma does and does not say. It was never the claim that DNA only ever makes RNA in a single tidy line. Some viruses run RNA back into DNA (reverse transcription), and RNA can copy RNA. The genuine, never-violated rule is narrower: information never flows from protein back into DNA or RNA. The word 'dogma' was an unfortunate choice by Francis Crick, who coined it in 1958 and later admitted he had not really understood what the word meant; it is a well-tested generalization, not an article of faith.
When your body makes insulin, the insulin gene in your DNA is first transcribed into messenger RNA, that mRNA is then translated into the insulin protein, and the protein goes off to manage your blood sugar. DNA to RNA to protein, exactly as the dogma describes.
Making insulin walks the whole central-dogma path from gene to working protein.
The dogma's real rule is that information never flows out of protein, not that DNA only ever goes forward. Reverse transcription (RNA back to DNA) is allowed and is how retroviruses like HIV work.