Acids ribonucleic

The primary structure of RNA is the same as DNA, with two exceptions. Ribose (Fig. 6.15) is the sugar component rather than deoxyribose, while uracil (Fig. 6.16) replaces thymine as one of the bases. 

Base pairing between nucleic acid bases can occur in RNA with adenine pairing with uracil, and cytosine pairing with guanine. However, the pairing is between bases within the same chain, and it does not occur for the whole length of the molecule (e.g. Fig. 6.18). Therefore, RNA is not a double helix, but it does have regions of helical secondary structure. 

Since the secondary structure is not uniform along the length of the RNA chain, more variety is allowed in RNA tertiary structure. Three types of RNA molecules have been identified with different cell functions. The three are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). 

Messenger RNA is responsible for relaying the code for one particular protein from the DNA genetic bank to the protein production site . The segment of DNA required is copied by a process called transcription. The DNA double helix unravels and the stretch which is exposed acts as a template on which the mRNA can be built (Fig. 6.17). Once complete, the mRNA leaves to seek out rRNA, while the DNA reforms the double helix. 

Ribosomal RNA can be looked upon as the production site for protein synthesis. It binds to one end of the mRNA molecule, then travels along it to the other end, reading the code and constructing the protein molecule one amino acid at a time as it moves along (Fig. 6.19). There are two segments to the rRNA known as the 50S and 30S subunits. 

Garrett, Reginald H., and Grisham, Charles M. (2002). Principles of Biochemistry With a Human Focus. Fort Worth, TX Harcourt College Publishers. 

Robinson, Corinne H. Lawler, Marilyn R. Chenoweth, Wanda L. et al. (1986). Normal and Therapeutic Nutrition, 17th edition. New York Macmillan. 

Nutrition.org. Information available from http //www.nutrition.org . 

DNA deoxyribonucleic acid—the natural polymer that stores genetic information in the nucleus of a cell 

Ribonucleic acid (RNA) is a nucleic acid, like DNA, and is also made up of sugars, phosphates, and nitrogenous bases (or just a base). It contains a ri-bose sugar, whereas DNA contains a deoxyribose sugar. The four main bases found in RNA are guanine (G), cytosine (C), uracil (U), and adenine (A). DNA contains thymine (T) instead of uracil. 

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D-ribose, CjHioOj. M.p. 87 0. The sugar of ribonucleic acid it is therefore present in all plant and animal cells. It has the furanose structure shown. 

A solution leading to a successful algorithm was recently found for the folding of ribonucleic acid (RNA) [36], Natural RNA polymers (figure C2.14.1) are mainly made up from four different bases . A, C, G and U. As with DNA, multiple hydrogen bonding favours the fonnation of G-C and A-U pairs [16, 37, 38] which leads to the appearance of certain characteristic stmctures. Loop closure is considered to be the most important folding event. 

Nucleic acids are acidic substances present m the nuclei of cells and were known long before anyone suspected they were the primary substances involved m the storage transmission and processing of genetic information There are two kinds of nucleic acids ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) Both are complicated biopolymers based on three structural units a carbohydrate a phosphate ester linkage between carbohydrates and a heterocyclic aromatic compound The heterocyclic aro matic compounds are referred to as purine and pyrimidine bases We 11 begin with them and follow the structural thread... 

Section 28 7 Nucleic acids are polynucleotides present m cells The carbohydrate component is D nbose m ribonucleic acid (RNA) and 2 deoxy d ribose m deoxyribonucleic acid (DNA)... 

When the cell requires instructions for protein production, part of the code on DNA, starting at an initiator and ending at a stop codon, is converted into a more mobile form by transferring the DNA code into a matching RNA code on a messenger ribonucleic acid (mRNA), a process known as transcription. The decoding, or translation, of mRNA then takes place by special transfer ribonucleic acids (tRNA), which recognize individual codons as amino acids. The sequence of amino acids is assembled into a protein (see Proteins section). In summary, the codes on DNA... 

A chain of nucleotides containing only deoxyribose as the sugar is a DNA. Similarly, RNA possesses chains nucleotides having only ribose as the sugar and is therefore a ribonucleic acid. 

Benzylamine Purine. The purine 6-benzylaminopurine [1214-39-7] (13) is an analogue of the natural product adenine, a component of both deoxyribonucleic acid and ribonucleic acid. It is not employed alone, but rather in combination with the natural products GA and GA to improve the size, weight, and thereby, yield per hm of Red DeHcious apples (10,24,25). Compounds with cytokinin activity were reported in 1913 (26) and asymmetric growth in apples was pubHshed in 1968 (27). 

KhGH A natural, stmctural variant of hGH called 20-K hGH has been reported to occur in the pituitary as well as in the bloodstream (12,13). This variant, which lacks the 15 amino acid residues from Glu-32 to Gln-46, arises from an alternative splicing of the messenger ribonucleic acid (mRNA) (14). This variant shares many but not all of the biological properties of hGH. 

Nucleic acid (deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)) probes utilize labeled, ie, radioactive, enzymatic, or fluorescent, fragments of DNA or RNA (the probe) to detect complimentary DNA or RNA sequences in a sample. Because the probe is tailored for one specific nucleic acid, these assays are highly specific and very sensitive (45). 

Nucleic Acids. Phosphoms is an essential component of nucleic acids, polymers consisting of chains of nucleosides, a sugar plus a nitrogenous base, and joined by phosphate groups (43,44). In ribonucleic acid (RNA), the sugar is D-ribose in deoxyribonucleic acids (DNA), the sugar is 2-deoxy-D-ribose. 

Cellular protein biosynthesis involves the following steps. One strand of double-stranded DNA serves as a template strand for the synthesis of a complementary single-stranded messenger ribonucleic acid (mRNA) in a process called transcription. This mRNA in turn serves as a template to direct the synthesis of the protein in a process called translation. The codons of the mRNA are read sequentially by transfer RNA (tRNA) molecules, which bind specifically to the mRNA via triplets of nucleotides that are complementary to the particular codon, called an anticodon. Protein synthesis occurs on a ribosome, a complex consisting of more than 50 different proteins and several stmctural RNA molecules, which moves along the mRNA and mediates the binding of the tRNA molecules and the formation of the nascent peptide chain. The tRNA molecule carries an activated form of the specific amino acid to the ribosome where it is added to the end of the growing peptide chain. There is at least one tRNA for each amino acid. 

Selenocysteine was identified in 1976 (57) in a protein produced by Clostridium stricklandii, and it is thought to be the form in which selenium is incorporated, stoichiometricaHy, into proteins. Studies with rats show that over 80% of the dietary selenium given them is incorporated into proteins, thus selenocysteine takes on metaboHc importance. Selenoproteins having known enzymatic activities contain selenocysteine at the active sites. Two other forms of metabohc selenium are recognized methylated selenium compounds are synthesized for excretion, and selenium is incorporated into some transfer ribonucleic acids (tRNAs) in cultured cells (58). Some of the more important seleno-compounds are Hsted in Table 4. Examples of simple ring compounds are shown in Eigure 4. 

Fohc acid is a precursor of several important enzyme cofactors required for the synthesis of nucleic acids (qv) and the metaboHsm of certain amino acids. Fohc acid deficiency results in an inabiUty to produce deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and certain proteins (qv). Megaloblastic anemia is a common symptom of folate deficiency owing to rapid red blood cell turnover and the high metaboHc requirement of hematopoietic tissue. One of the clinical signs of acute folate deficiency includes a red and painhil tongue. Vitamin B 2 folate share a common metaboHc pathway, the methionine synthase reaction. Therefore a differential diagnosis is required to measure foHc acid deficiency because both foHc acid and vitamin B 2 deficiency cause... 

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