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Central to all life is the transfer of information stored in our genes into molecules that are used to make proteins. How this happens has long been inferred but never directly seen. Now scientists have captured videos of some of the key steps of gene expression – how a gene is “turned on” to make a protein — in living cells. What they have found is surprising.
Read more: What does it look like to “turn on” a gene?
Video Transcript:
These bursts of color aren’t fireworks. They’re much smaller. These are genes inside a cell, springing to action. Each cell in our body — skin, muscles, brain or gut — contains the same set of genes, about 20,000 in total. These genes carry instructions for making proteins, which form many parts of the body and do countless jobs there.
To make a protein, the cell first needs to copy the DNA containing those instructions. It’s called “transcription” and a large cast of players make it happen. Then, special molecular machinery reads the copy and builds the protein. But if all cells contain the same genes, how does one cell differ from the next? It all depends on which genes are turned on, and when. Today, powerful technologies allow scientists to see transcription in action, in real time, in living cells.
Back to our fireworks: The glowing green is a stretch of DNA right next to the gene. It’s called a “promoter.” The blue is a stretch of DNA far away from the gene; it’s called an “enhancer.” To turn a gene on, the promoter and enhancer have to practically touch. And when they do, copies of the gene are made — that’s the pink flashes. But promoters and enhancers don’t act alone. Transcription factors must bind to the DNA. The red zigzagging dots you see here are many copies of one kind of transcription factor in a mouse cell.
Scientists have found that many transcription factors bind to DNA for only a few seconds. Now, the crucial molecular workhorse called “RNA polymerase” can come in and copy the gene. The RNA polymerase has a team of helpers, called the “mediator complex” — that’s these green proteins. They gather around the RNA polymerases and help them make mRNA copies — that’s the pink you see here. Once mRNA is made, it needs to journey out of the cell’s nucleus and into the cytoplasm. The cell will use the mRNA instructions to build a protein. Scientists used to think that mRNA was carefully transported, but it isn’t — mRNA molecules bounce around until they find an exit. After all that activity, the cell can now make the protein it needs.
