RNA SYNTHESIS: TRANSCRIPTION
The process of converting the information contained in a DNA segment into proteins begins with the synthesis of mRNA molecules containing anywhere from several hundred to several thousand ribonucleotides, depending on the size of the protein to be made. Each of the 100,000 or so proteins in the human body is synthesized from a different mRNA that has been transcribed from a specific gene on DNA.
One question which you must ask yourself is:
"Why do we need mRNA if DNA holds all the genetic information, the instructions for the proteins the cell is supposed to produce?"
The answer for eukaryotic cells (those cells with a nucleus) is the importance of DNA. If DNA is damaged in any way, then the coding sequence is changed and a mutation could result which could greatly affect the cell or even the whole organism! You'll learn more about this when we discuss mutations in class. Because of this, the DNA should be protected as much as possible.
If the DNA were to venture out into the cytoplasm where the ribosomes are in order to give the instructions for which proteins were to be made, then it would be more vulnerable to damage from:
UV light , or
This presents a problem, however...
How is the DNA supposed to get the information it encodes out to the ribosomes which carry out the instructions in the cytoplasm?
The answer is that there must be a MESSENGER. This messenger is mRNA!