Re: What happens in DNA copying? When does it occur in the cell?

The genetic information that makes us who we are is encoded into our DNA as a sequence of chemical letters. However, in order to use the information, DNA has to be copied. DNA is all coiled up in the nucleus of cells. So to make copies, the DNA has to be "unpackaged," and then a number of proteins have to bind in place. The key copying protein is called RNA polymerase. It starts at a very specific spot on the DNA strand and makes a RNA copy of the genetic information. It doesn't copy the entire DNA strand, it only copies the part that is necessary -- this bit of DNA sequence is a gene. The copy of the gene is then processed and transported out of the nucleus of the cell into the cytoplasm. This messenger RNA (mRNA) copy is then used to make a protein. This process of making the DNA copy is called transcription.

Transcription occurs at different times, this depends on the type of cell (muscle, skin, bone, nerve etc.). mRNA doesn't last forever so for cells that are constantly making new proteins, they have to make new mRNA too.

We have a new web site with some pretty cool 3-D animations, one is on transcription. Go to DNA Interactive, click on Code, click on Copying the Code, then pick Putting it All Together. The 3-D animation is there.