DNA And RNA

DNA is the molecule of heredity in all prokaryotic and eukaryotic organisms. Although nucleic acids are discovered and chemically characterized more than hundred years ago, their genetic role was not known until the transformation experiment by Griffith. Two major nucleic acids - DNA and RNA are composed of un-branched chains of subunits called nucleotides, each nucleotide containing phosphate, a pentose and a nitrogenous base. The bonds between the paired bases are relatively weak, allowing the DNA molecule to be unzipped prior to the processes of replication or transcription.

DNA is permanently locked into the nucleus. But the machinery for protein synthesis is situated in the cytoplasm - outside the cell membrane. DNA communicates with this machinery through a messenger molecule known as RNA. The messenger RNA is chemically similar to DNA itself, but has a single rather than a double backbone and the base Uracil takes the place of DNA’s a thymine. When a gene is active, the DNA base sequence corresponding to that gene is transcribed into the mRNA.

The structure of DNA is crucial to its role as the cells information.

All cellular DNA consist of two very long, helical poly-nucleotides chain coiled around a common axis. The two strands of the double helix run in opposite directions, the two strands being held together by hydrogen bonds between nitrogenous bases. Adenine is always paired with thymine and guanine is always paired with cytosine. There are two hydrogen bonds between adenine and thymine whereas three hydrogen bonds between guanine and cytosine.

RNA is the chemical that controls the synthesis of protein in a cell and is the genetic material in some viruses. The molecules of RNA in a cell are copied from DNA and consist of a single strand of nucleotides, each containing the sugar ribose, phosphoric acid and one of the four bases Adenine, Guanine.

Most RNA's are formed by a single polynucleotide twisted about itself in certain regions, thereby forming a periodic double helical structure. In most of all organisms the RNA serves three primary functions. The messenger RNA’s which constitutes only 5% of total RNA contains the sequences of nucleotides that specify the primary structures of the cell’s proteins.

Transfer RNA's transports the amino acids to the site of protein synthesis (mRNA ribosome complex) during translation. The Ribosomal RNA constitutes about 80% of the total RNA’s in a cell. They serve as the functional components of the cells ribosome’s which participate in protein synthesis. A cell’s RNA’s are produced by transcription of its DNA.

These two major nucleic acids DNA and RNA are composed of un-branched chains of subunits called nucleotides and each nucleotide containing phosphate, a pentose and a nitrogenous base.