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D- NUCLEOTIDE

D- NUCLEOTIDE. Ribonucleoside and deoxyribonucleoside phosphates (nucleotides) are essential for all cells. Without them, neither DNA nor RNA can be produced, and therefore proteins cannot be synthesized or cells proliferate.

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D- NUCLEOTIDE

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  1. D-NUCLEOTIDE

  2. Ribonucleoside and deoxyribonucleoside phosphates (nucleotides) are essential for all cells. Without them, neither DNA nor RNA can be produced, and therefore proteins cannot be synthesized or cells proliferate. Nucleotides also serve as carriers of activated intermediates in the synthesis of some carbohydrates, lipids, and proteins and are structural components of a number of essential coenzymes such as coenzyme A, FAD, NAD+, and NADP+. Nucleotides play an important role as "energy currency" in the cell. Nucleotides are important regulatory compounds for many of the pathways of intermediary metabolism, inhibiting or activating key enzyme.

  3. Nucleotide structure Nucleotides are composed of a nitrogenous base, a pentose monosaccharide, and one, two, or three phosphate groups. The nitro-gen-containing bases belong to two families of compounds: the purines and the pyrimidines.

  4. Purine and pyrimidine structures

  5. Nucleosides The addition of a pentose sugar to a base produces a nucleoside. The ribonucleosides of A, G, C, T, and U are named adenosine, guanosine, cytidine, thymidine, and uridine respectively. If the sugar is ribose, a ribonucleoside is produced; if the sugar is 2-deoxyribose, a deoxyribonucleoside is produced.

  6. Note that the atoms in the rings of the bases are numbered 1 to 6 in pyrimidines, and 1 to 9 in purines, whereas the carbons in the pentose are numbered 1' to 5'.

  7. Nucleotides Nucleotides are mono-, di-, or triphosphate esters of nucleosides. The phosphate group is attached by an ester linkage to the 5'-OH of the pentose. Such a compound is called a nucleoside 5'-phos-phate or a 5'-nucleotide. If one phosphate group is attached to the 5'-carbon of the pentose, the structure is a nucleoside monophosphate (NMP) like AMP or CMP. If a second or third phosphate is added to the nucleoside, a nucleoside diphosphate (for example, ADP) or triphosphate (for example, ATP) results.

  8. Several of the most important coenzymes are nucleotides. These include coenzyme A and the coenzymes of oxidation and reduction, nicotinamide adenine dinucleotide (NAD), nicotinamide adenine dinucleotide phosphate (NADP), flavine adenine dinucleotide (FAD) and flavine mononucleotide (FMN).

  9. Adenosine monophosphate is a component of each of these molecules except FMN. Uridine diphosphate (UDP) is used as a carrier of activated glucose units. Its structure is the same as adenosine-5'-diphosphate except that adenine is replaced by uracil. UDP-glucose has an ester linkage between carbon one of glucose and the terminal phosphate group of UDP.

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