Ribose Nucleic Acids

Ribose Nucleic Acids - Most cellular RNA is single stranded, although some viruses have double stranded RNA. The single RNA strand is folded upon itself, either entirely or in certain regions. In the folded region a majority of the bases are complementary and are joined by hydrogen bonds. This helps in the stability of the molecule. In the unfolded region the bases have no complements. Because of this RNA does not have the purine pyrimidine equality that is found in DNA.

RNA also differs from DNA in having ribose as the sugar instead of deoxyribose. The common nitrogenous bases of RNA are adenine, guanine, cytosine and uracil. Thus the pyrimidine uracil substitutes thymine of DNA. In regions where purine pyrimidine pairing takes place, adenine pairs with uracil and guanine with cytosine. In addition to the four bases mentioned above, RNA also has some unusual bases.

There are more unusual bases in RNA than in DNA. All normal RNA chains either start with adenine or guanine:

Three types of cellular RNA have been distinguished: messenger RNA (mRNA) or template RNA, ribosomal RNA (rRNA) and soluble RNA (sRNA) or transfer RNA (tRNA).Ribosomal and transfer RNA comprise about 98% of all RNA.All three forms of RNA ar          e made on a DNA template. (It was once suggested that tRNA and rRNA were not formed on DNA but were self replicating).

Transfer RNA and messenger RNA are synthesized on DNA templates of the chromosomes, while ribosomal RNA is derived from nucleolar DNA. The three types of RNA are synthesized during different stages in early development. Most of the RNA synthesized during cleavage is mRNA. Synthesis of tRNA occurs at the end or cleavage, and rRNA synthesis begins during gastrulation.