Genetic information in DNA is first copied to form an RNA molecule, in a process known as
transcription. The RNA used to make proteins is called messenger RNA (mRNA) because it carries information from the DNA to the ribosome, where protein synthesis occurs.
The mRNA serves as a template to guide protein synthesis. Scientists refer to protein synthesis as "translation" because ribosomes translate an mRNA sequence into a protein sequence. Prokaryotic cells use the mRNA directly as a template for protein synthesis.
Eukaryotic cells, however, must modify the precursor mRNA in several ways before it can be used to guide protein synthesis. The two ends are chemically altered, and sections of the RNA that do not encode protein sequences, called introns, are spliced out. Together, these modifications are called "mRNA processing." After processing, the mature mRNA moves from the nucleus into the cytoplasm, where it binds to the ribosome and serves as a template for synthesis of a protein.
The most important stage for the regulation of most genes is when transcription begins. This is because it costs the cell less energy to regulate transcription than to regulate the steps after transcription.
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