Genes are functional segments of DNA molecules. DNA stores genetics information. The information can be “read” through transcription and translation. Transcription is a process that RNA is synthesized from DNA templates, and translation is a process where proteins are synthesized using RNA as templates. This whole process from DNA to its final protein product is called “the central dogma”.
DNA is a very long thread like, double stranded molecule made up of a very large number of deoxyribonucleotides joined together. Deoxyribonucleotide is made up of a sugar called deoxyribose, a nitrogenous base and a phosphate group. DNA is located in the nucleus. DNA bears a physical structure of anti parallel double helix. The two stands run in opposite directions and are parallel to each other. DNA is highly organized in cells, first coils into nucleosomes and then into chromatins.
RNA molecules are transcribed from DNA templates. RNA is similar to DNA in terms of structure and composition. However, RNA is made of 4 bases A, U, G and C; and ribose replaces deoxyribose in DNA. RNA molecules are smaller and are single-stranded. There are four different types of RNA: mRNA, tRNA, rRNA and ncRNA. Most RNA molecules usually have secondary structure, consisting of stems and loop domains. mRNA is linear in structure, variable in size, has a poly A tail and acts as a template for protein synthesis. tRNAs carry amino acids to protein synthesis sites. rRNA is structural component for ribosomes where proteins are made. NcRNA is a novel type of small RNA which plays a role in regulation of many cellular processes. All RNAs are associated in the production of a protein.
The Central Dogma and Genetic Code
DNA can replicate itself according to base-paring mechanism. RNA is made from DNA template, also via base-paring mechanism. mRNA is read in triplet code called genetic code. Three adjacent nucleotides on mRNA determine an amino acid on protein. The code starts from a fixed point and continues undisrupted. Genetic codes are degenerative because there are only 20 amino acids and 64 combinations of 4 nucleotides.
Mutation, Genetic disease and Gene Therapy
Many factors may cause mutations in DNA. The consequence is that gene function is compromised or stopped. Mutations occurring in germ line cells may cause genetic diseases. For these mutated DNA, gene therapy can provide an effective cure