The two strands of the helix run in opposite directions (1 "up" and 1 "down"). The inner edges of the helices are formed by the nitrogenous bases and they run in pairs. Adenine pairs with thymine with 2 hydrogen bonds and cytosine pairs with guanine with 3 hydrogen bonds (Murray et al, 2007).
DNA is present in the chromosomes of most of the living beings. The human genome approximately has 3 billion base pairs of DNA which are arranged in the 23 pairs of chromosomes. Sequence pieces of DNA form genes which carry vital information. The genetic information is achieved by complementary base pairing. Transmission, transcription and translation are the steps involved in transmission of genetic information. Currently, DNA is used in the field of genetic engineering for the treatment of many diseases (Murray et al, 2007).
RNA or ribonucleic acid is similar to DNA except that it is single stranded and the sugar present in it is ribose sugar. RNA consists of repeating units of nucleotides which are made up of a nitrogenous base, a ribose sugar and a phosphate. The pyramidines are guanine and cytosine and the purines are adenine and uracil. RNA is transcribed from DNA by the enzyme called RNA polymerase. There are basically 2 types of RNA: coding RNAs and non-coding RNAs. Messenger RNA (mRNA) is a coding RNA. There are many non-coding RNAs. These include ribosomal RNA (rRNA), transfer RNA (tRNA) and others.
mRNA carries information from DNA to the ribosome which is the site of synthesis for proteins. The amino acid sequence in the protein is based on the coding sequence of the mRNA. tRNA and rRNA are involved in the process of translation. Many other non-coding RNAs are involved in RNA processing, gene regulation, catalysis of chemical reactions, cutting and ligation of other RNA molecules, catalysis of peptide bond formation in the ribosomes and other roles (Murray et al, 2007).
Carbohydrates are organic compounds that are either ketones or aldehydes with many hydroxyl groups added. These hydroxyl groups are added one on each carbon atom that is not a part of either the aldehyde or the ketone group. Thus the general formula of a carbohydrate can be designated as (C'H2O)n. Here n is any number greater than 3. There are many carbohydrates like uronic acids and fucose which don't have this formula in their structure. Also, all chemicals which have this structure do not fall into the category of carbohydrates. The basic carbohydrate units are monosaccharides. These are further classified based on the number of carbon atoms, the placement of the carbonyl group and the chiral handedness. Monosaccharides with the carbonyl group aldehyde are known as aldoses, those with carbonyl group ketone are known as ketoses, those with three carbon atoms are known as trioses, those with four are called tetroses, five are called pentoses and six are hexoses. Each carbon atom with a hydroxyl group (except the first and last carbon atoms) is assymmetric making them stereocenters with either right-side configuration or left-side configuration. Thus many isomers can exist for any given monosaccharide formula. Glucose, galactose and fructose are monosaccharides. Monosaccharides can link together in many ways to form disaccharides and poly- saccharides. One or