Ribonucleic acid major types

The position was somewhat clarified by the isolation of 2- and 3-O-phos-phonucleosides from ribonucleic acid hydrolyzates in 92 to 100% yields,134 and also by the demonstration that 5-O-phosphonucleosides are also present in enzymic digests.49, 197 Yet this information gave no indication of the nature of the alkali-labile linkages. Thus, while the majority of the experimental evidence pointed to the phosphoryl residues as being doubly esterified with adjacent nucleosides, two facts remained apparently inexplicable on the basis of this type of structure. First, ready fission by alkalis, and secondly, the absence of 5-phosphates from alkaline hydrolyzates and their presence in enzymic digests. Both these facts have been explained by Brown and Todd in the following way.92... 

The nucleic acids play a central role in the storage and expression of genetic information (see p. 236). They are divided into two major classes deoxyribonucleic acid (DNA) functions solely in information storage, while ribonucleic acids (RNAs) are involved in most steps of gene expression and protein biosynthesis. All nucleic acids are made up from nucleotide components, which in turn consist of a base, a sugar, and a phosphate residue. DNA and RNA differ from one another in the type of the sugar and in one of the bases that they contain. 

Transcription starts with the process hy which the genetic information is transcribed onto a form of RNA, called mRNA. Ribonucleic acid, RNA, is structurally similar to DNA with the exceptions that its nucleotides contain ribose, instead of a 2 -deoxyribose, and the base thymine is replaced by uracil. There are three major types of RNA depending on their specific functions. However, all three types of RNA are much smaller than DNA and they are single stranded, rather than double stranded. 

A typical molecular analysis of various micro-organisms is shown in Table 5.9U ) Most of the elemental composition of cells is found in three basic types of materials—proteins, nucleic acids and lipids. In Table 5.10, the molecular composi-tion of a bacterium is shown in more detail. Water is the major component of the cell and accounts for 80-90 per cent of the total weight, whilst proteins form the next most abundant group of materials and these have both structural and functional properties. Most of the protein present will be in the form of enzymes. Nucleic acids are found in various forms—ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Their primary function is the storage, transmission and... 

The major nucleic acid in the nucleus of cells is deoxyribonucleic add (or DNA). It contains the pentose sugar deoxyribose as one of its chemical constituents. DNA is now known to be the genetic material. Another type of nucleic acid, ribonucleic acid (or RNA), contains ribose instead of deoxyribose. Its main role is in the transmission of the genetic information from DNA into protein. 

In bacterial cells, nucleic acids are found in the form of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA carries the genetic blueprint for the cell and RNA acts as an intermediary molecule to convert the blueprint into proteins [8]. RNA has three forms namely, ribosomal, messenger and transfer RNAs. All the three types of RNA are essential for protein synthesis. Ribosomal RNA is the most abundant macromolecule, next to proteins, in an actively growing prokaryotic cell. It is a major component of the ribosome, the cellular machinery used to synthesize new proteins. There are three ribosomal RNA molecules in prokaryotes namely 5S (ca. 120 nucleotides), 16S (1500 nucleotides), and 23S (2900 nucleotides). 

Ribonucleic acids are synthesized from the DNA template through transcription. The mononucleotides contain ribose. Unlike DNAs, RNAs are single stranded, although twisting may occur in a complementary fashion matching base pairs. RNAs are much lower in molecular weight than DNAs. The three major types—messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)—are involved in a multistep process of protein synthesis (56,57). 

Ribonucleic Acid. A major contribution to the formulation of RNA structure was the demonstration that alkaline hydrolysis of RNA quantitatively liberates about equal amounts of mononucleotide isomers of all four bases 103). Although it was readily established that none of these mononucleotides is the 5 -phosphate isomer, it was not until some years later that Cohn and associates 103) by controlled degradation experiments, and Brown and associates 121) by the synthetic route, established that the products were isomers involving phosphate attachment at positions 2 and 3 of the ribose. Of equal significance was the discovery 161) that hydrolysis of RNA by the enzyme phosphodiesterase (snake venom or intestinal) liberates mononucleotides exclusively of still another type, the 5 -mono-nucleotides. It was thus necessary to establish the mechanisms which could account for one phosphodiester structure in the RNA chain giving rise to three isomers of each mononucleotide. 

We have studied two of the three major kinds of biopolymers polysaccharides in Chapter 21 and proteins in Chapter 22. Now we will look at the third kind of biopolymer—nucleic acids. There are two types of nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DMA encodes an organism s entire hereditary information and controls the growth and division of cells. In all organisms (except certain viruses), the genetic information stored in DNA is transcribed into RNA. This information can then be translated for the synthesis of all the proteins needed for cellular structure and function. 

How does nature assemble proteins The answer to this question is based on one of the most exciting discoveries in science, the nature and workings of the genetic code. AU hereditary information is embedded in the deoxyribonucleic acids (DNA). The expression of this information in the synthesis of all proteins, including the many enzymes necessary for cell function, is carried ont by the ribonucleic acids (RNA). After the carbohydrates and polypeptides, the nncleic acids are the third major type of biological polymer. This section describes their strnctnre and fnnction. 

RNA Ribonucleic acid linear copolymers usually of four ribonucleotides. Three major types of RNA are synthesized in the cell ribosomal RNA (rRNA), the major component of ribosomes transfer RNA (tRNA), the adaptor for protein synthesis and messenger RNA (mRNA), which is required for information transfer. Other small RNAs with specialized functions are also synthesized in small amounts in both prokaryotic and eukaryotic cells. 

Two major types of nucleic acids are DNA (deoxyribonucleic acid), and RNA (ribonucleic acid). Both of them contain phosphate groups. These phosphate groups alternate with sugars to form the backbone of the molecule. The sugars are deoxyribose in the case of DNA and ribose in the case of RNA. Attached to each sugar is a purine or a pyrimidine base. The purine bases are adenine and guanine. One pyrimidine base is cytosine. In the case of RNA the other pyrimidine base is uracil, while for DNA the other pyrimidine base is thymine. 49. The complementary sequence to AGO is TCG. 

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