Explain how RNA are synthesized.?

Answer 1

RNA is a large nucleic acid molecule found in the nucleus but mainly in the cytoplasm of a cell where it is associated with microsomes; consists of a linear polymer of nucleotides; it transmits genetic information from DNA to the cytoplasm and controls certain chemical processes in the cell.
RNA is a linear polymer of four different nucleotides. Each nucleotide is composed of three parts: a five-carbon sugar known as ribose, a phosphate group, and one of four bases attached to each ribose, either adenine (A), cytosine (C), guanine (G), or uracil (U). The structure of RNA is basically a repeating chain of ribose and phosphate moieties, with one of the four bases attached to each ribose.In this templating scheme, the DNA base T specifies A in the RNA, A specifies U, C specifies G, and G specifies C.

Synthesis of RNA is usually catalyzed by an enzyme - RNA polymerase, using DNA as a template. Initiation of synthesis 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’ -> 5’ direction, synthesizing a complementary RNA molecule with elongation occurring in the 5’ -> 3’ direction. The DNA sequence also dictates where termination of RNA synthesis will occur.

There are also a number of RNA-dependant RNA polymerases as well 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, it is known that RNA-dependent RNA polymerases are required for the RNA interference pathway in many organisms.

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