<P> Carbohydrates are aldehydes or ketones, with many hydroxyl groups attached, that can exist as straight chains or rings . Carbohydrates are the most abundant biological molecules, and fill numerous roles, such as the storage and transport of energy (starch, glycogen) and structural components (cellulose in plants, chitin in animals). The basic carbohydrate units are called monosaccharides and include galactose, fructose, and most importantly glucose . Monosaccharides can be linked together to form polysaccharides in almost limitless ways . </P> <P> The two nucleic acids, DNA and RNA, are polymers of nucleotides . Each nucleotide is composed of a phosphate attached to a ribose or deoxyribose sugar group which is attached to a nitrogenous base . Nucleic acids are critical for the storage and use of genetic information, and its interpretation through the processes of transcription and protein biosynthesis . This information is protected by DNA repair mechanisms and propagated through DNA replication . Many viruses have an RNA genome, such as HIV, which uses reverse transcription to create a DNA template from its viral RNA genome . RNA in ribozymes such as spliceosomes and ribosomes is similar to enzymes as it can catalyze chemical reactions . Individual nucleosides are made by attaching a nucleobase to a ribose sugar . These bases are heterocyclic rings containing nitrogen, classified as purines or pyrimidines . Nucleotides also act as coenzymes in metabolic - group - transfer reactions . </P> <P> Metabolism involves a vast array of chemical reactions, but most fall under a few basic types of reactions that involve the transfer of functional groups of atoms and their bonds within molecules . This common chemistry allows cells to use a small set of metabolic intermediates to carry chemical groups between different reactions . These group - transfer intermediates are called coenzymes . Each class of group - transfer reactions is carried out by a particular coenzyme, which is the substrate for a set of enzymes that produce it, and a set of enzymes that consume it . These coenzymes are therefore continuously made, consumed and then recycled . </P> <P> One central coenzyme is adenosine triphosphate (ATP), the universal energy currency of cells . This nucleotide is used to transfer chemical energy between different chemical reactions . There is only a small amount of ATP in cells, but as it is continuously regenerated, the human body can use about its own weight in ATP per day . ATP acts as a bridge between catabolism and anabolism . Catabolism breaks down molecules, and anabolism puts them together . Catabolic reactions generate ATP, and anabolic reactions consume it . It also serves as a carrier of phosphate groups in phosphorylation reactions . </P>

Which process in the body produces nitrogenous wastes