Gene expression · Lobeworks/17
Gene expression is the way a cell turns the instructions stored in its DNA into working proteins: a gene is copied into a messenger RNA, and the RNA is read by ribosomes that string amino acids together into the protein it encodes.
Gene expression. Gene expression is the way a cell turns the instructions stored in its DNA into working proteins: a gene is copied into a messenger RNA, and the RNA is read by ribosomes that string amino acids together into the protein it encodes.
DNA stays in the nucleus. To use a gene, the cell first copies its sequence into messenger RNA (transcription); the RNA leaves the nucleus and ribosomes in the cytoplasm read it three letters at a time, each triplet naming one amino acid (translation). The chain then folds into its shape, and the shape is the function: a pump, a receptor, an ion channel, an enzyme. The human genome holds about 20,000 protein-coding genes, and every cell carries all of them; a neuron differs from a liver cell by which ones it switches on.
Proteins called transcription factors decide which genes are read. Some answer to signals from outside: cortisol, a steroid, crosses the membrane and binds receptors that act as transcription factors, which is why its effects build over hours and outlast the stress that released it.
Lasting memory needs new proteins. Short-term changes at a synapse reuse what is already there; the late, durable phase of long-term potentiation depends on genes being switched on and new proteins made.
A mutated gene makes a changed protein. A single wrong letter in the gene of a channel can change how a neuron fires, which is how some epilepsies are inherited.
Proteins wear out and are replaced. Folding, repair and removal are kept in balance by proteostasis, and its failure over decades is a thread through neurodegenerative disease.
DNA is the library, RNA the photocopy, the protein the machine built from it.
The cell never sends the original out; it copies the page it needs and builds from the copy.
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