transcription
/ tran-SKRIP-shun /
Your DNA is a precious, irreplaceable archive — you only get one copy, and damaging it is dangerous. So the cell almost never uses the original directly. Instead, when it needs to act on a gene, it makes a working copy in a slightly different material called RNA. Transcription is that copying step: the cell reads one gene off its DNA and writes out a matching RNA strand it can use, reuse, and throw away without touching the master file.
Mechanically, transcription works because of the same base-pairing that holds DNA together. A protein machine called RNA polymerase clamps onto the DNA, unzips a short stretch, and slides along one of the two strands. As it moves, it reads each DNA letter and adds the RNA letter that pairs with it: where the DNA says C the RNA gets G, where it says A the RNA gets U (RNA uses uracil, U, in place of DNA's thymine, T). The result is a fresh RNA strand whose sequence faithfully mirrors the gene. The strand grows in one direction only, from its 5-prime end toward its 3-prime end.
Transcription matters because it is the cell's volume control over the genome. Every cell in your body carries the same DNA, but a muscle cell and a nerve cell look and behave completely differently because they transcribe different genes, at different times, in different amounts. Turning transcription up or down is the main way cells specialize, respond to signals, and adapt — which makes the machinery that starts and stops transcription one of the most heavily regulated systems in all of biology.
When you start fasting, your liver cells crank up transcription of genes for burning fat, producing many fresh RNA copies of those genes so the liver can make more of the fat-burning enzymes — the same DNA, just read out louder.
Fasting raises transcription of fat-burning genes — the cell turns the volume up, not the DNA itself.
Transcription copies DNA into RNA; it does not make protein. The step that reads RNA into protein is translation, a separate process.