Messenger ribonucleic acid , signal

The functional modulation of the effect of cytokines requires the presence of cellular and soluble receptors. The expression of these receptors is regulated by specific signals, often dependent on cytokine networks. Transiently produced and of short half-life, cytokines are typically not stored as preformed molecules, and their production is dependent on transient genetic transcriptional activation and short-lived messenger ribonucleic acid (mRNA). Cytokines are rapidly secreted, leading to a brief burst of cytokine release. This burst is very important for cytokines to achieve distant activities, contrasting with the small amount of these molecules necessary for local functions (see later section on interleukin-1). 

The information which specifies the amino-acid sequence of a protein is stored in the nucleotide sequence of the double helix of deoxyribonucleic acid (DNA). The transcription of sections of this information into ribonucleic acid (RNA) is catalysed by RNA polymerases. These enzymes not only control the synthesis of RNA but also recognize stop and start signals on the DNA. The start signals are complex and may be blocked by repressor molecules which inhibit the transcription process. Once synthesized, the (messenger) RNA is processed and exported to ribosomes where its nucleotide sequence is translated into protein. Triplets of three nucleotides (codons) in the messenger RNA each specify (encode) one amino acid. The linear sequence of nucleotides in the messenger RNA thus specifies the sequence of amino acids in the protein whose primary structure will therefore correspond directly to the sequence of nucleotides in the DNA. 

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