Synthesis
Synthesis of RNA is usually catalyzed by an enzyme—RNA polymerase—using DNA as a template, a process known as transcription. Initiation of transcription begins with the binding of the enzyme to a promoter sequence in the DNA (usually found "upstream" of a gene). The DNA double helix is unwound by the helicase activity of the enzyme. The enzyme then progresses along the template strand in the 3’ to 5’ direction, synthesizing a complementary RNA molecule with elongation occurring in the 5’ to 3’ direction. The DNA sequence also dictates where termination of RNA synthesis will occur.
RNAs are often modified by enzymes after transcription. For example, a poly(A) tail and a 5' cap are added to eukaryotic pre-mRNA and introns are removed by the spliceosome.
There are also a number of RNA-dependent RNA polymerases that use RNA as their template for synthesis of a new strand of RNA. For instance, a number of RNA viruses (such as poliovirus) use this type of enzyme to replicate their genetic material. Also, RNA-dependent RNA polymerase is part of the RNA interference pathway in many organisms.
Read more about this topic: RNA
Famous quotes containing the word synthesis:
“Our art is the finest, the noblest, the most suggestive, for it is the synthesis of all the arts. Sculpture, painting, literature, elocution, architecture, and music are its natural tools. But while it needs all of those artistic manifestations in order to be its whole self, it asks of its priest or priestess one indispensable virtue: “faith.””
—Sarah Bernhardt (1845–1923)
“It is in this impossibility of attaining to a synthesis of the inner life and the outward that the inferiority of the biographer to the novelist lies. The biographer quite clearly sees Peel, say, seated on his bench while his opponents overwhelm him with perhaps undeserved censure. He sees him motionless, miserable, his head bent on his breast. He asks himself: “What is he thinking?” and he knows nothing.”
—Andre Maurois (1885–1967)
“If in the opinion of the Tsars authors were to be the servants of the state, in the opinion of the radical critics writers were to be the servants of the masses. The two lines of thought were bound to meet and join forces when at last, in our times, a new kind of regime the synthesis of a Hegelian triad, combined the idea of the masses with the idea of the state.”
—Vladimir Nabokov (1899–1977)