Ribonucleic acid 303 base sequences

The discovery of the base-paired, double-helical structure of deoxyribonucleic acid (DNA) provides the theoretic framework for determining how the information coded into DNA sequences is replicated and how these sequences direct the synthesis of ribonucleic acid (RNA) and proteins. Already clinical medicine has taken advantage of many of these discoveries, and the future promises much more. For example, the biochemistry of the nucleic acids is central to an understanding of virus-induced diseases, the immune re-sponse, the mechanism of action of drugs and antibiotics, and the spectrum of inherited diseases. 

The nucleic acids known as deoxyribonucleic acid (DNA) are the molecules that store genetic information. This information is carried as a sequence of bases in the polymeric molecule. Remarkably, the interpretation of this sequence depends upon simple hydrogen bonding interactions between base pairs. Hydrogen bonding is fundamental to the double helix arrangement of the DNA molecule, and the translation and transcription via ribonucleic acid (RNA) of the genetic information present in the DNA molecule. 

Nucleic Acid. A nucleic acid is a natural polynucleotide. It is a sugar-phosphate chain with purine and pyrimidine bases attached to it, as shown in Chart 10. If the sugar is deoxyribose and the pyrimidine bases are cytosine and thymine, the nucleic acid is deoxyribonucleic acid, DNA if the sugar is ribose, and the pyrimidine bases are (mostly) cytosine and uracil, the nucleic acid is ribonucleic acid, RNA. The sequence of bases may appear arbitrary and random, but it constitutes a meaningful code (see Code Word). In double-stranded nucleic acids,... 

The four bases whose sequence determines the hereditary information in ribonucleic acid (RNA), the naturally occurring polynucleotide, are adenine, cytosine, guanine, and uracil. These structures are as shown in Figure A. 

Figure 25-25 Structure of a ribonucleic acid (RNA) chain with the base sequence adenine, uracil, guanine, cytosine...

As much of the terminology used in molecular biology may be unfamiliar to some readers, it is appropriate to define some of the vocabulary and this is given in an appendix to this chapter. There are two types of nucleic acids, the ribonucleic acids (RNA) and the deoxyribonucleic acids (DNA). Genetic information is carried in the linear sequence of nucleotides in DNA. Each molecule of DNA contains two complementary strands of deoxyribonucleotides which contain the purine bases, adenine and guanine and the pyrimidines, cytosine and thymine. RNA is single-stranded, being composed of a linear sequence of ribonucleotides the bases are the same as in DNA with the exception that thymine is replaced by the closely related base uracil. DNA replication occurs by the polymerisation of a new complementary strand on to each of the old strands. 

For reduplication, the chains are separated and on each a new, complementary strand is synthesized by enzymes called DNA polymerases [652J. For protein biosynthesis, the DNA is copied (transcribed) into the messenger ribonucleic acid (mRNA) by the enzyme RNA polymerase (Fig. 20.2) where, in contrast to DNA, the deoxyribose is replaced by ribose and thymine by the equivalent uracil. Here again, the Watson-Crick base pair plays the crucial role so that the mRNA sequence is complementary to the DNA sequence. 

RNA Ribonucleic acid. A macromolecule made of nucleotide sequences similar to DNA, but with uracil instead of thymine as a base and ribose as the backbone sugar instead of deoxyribose. RNA plays a major role in transcription and translation of the genetic code. There are several classes of RNA including mRNA, tRNA and rRNA. 

Enzymes are biological catalysts, all of which are proteins, except for a class of RNA-modifying catalysts known as ribozymes ribozymes are molecules of ribonucleic acid that catalyse reactions on the phosphodiester bond of other RNAs. The International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers each enzyme is described by a sequence of one of four numbers preceded by EC . The first number broadly classifies the enzyme based on its mechanism. 

Yamada Y, Nagahama T, Kawasaki H, Banno 1 The phylogenetic relationships of the genera Phajfia Miller, Yoneyama et Soneda and Cryptococcus Kutzing emend. Phaff et Spencer (Cryptococcaceae) based on the partial sequences of 18S and 26S ribosomal ribonucleic acids. J Gen Appl Microbiol 1990 36 403 14. 

The structure proposed by Watson and Crick has two properties of central importance to the role of DNA as the hereditary material. First, the structure is compatible with any sequence of bases. The base pairs have essentially the same shape (see Figure 1.6) and thus fit equally well into the center of the double-helical structure of any sequence. Without any constraints, the sequence of bases along a DNA strand can act as an efficient means of storing information. Indeed, the sequence of bases along DNA strands is how genetic information is stored. The DNA sequence determines the sequences of the ribonucleic acid (RNA) and protein molecules that carry out most of the activities within cells. 

Ribonucleic acid is a class of polynucleotides, nearly all of which are involved in some aspect of protein synthesis. RNA molecules are synthesized in a process referred to as transcription. During transcription, new RNA molecules are produced by a mechanism similar to DNA synthesis, that is, through complementary base pair formation. The sequence of bases in RNA is therefore specified by the base sequence in one of the two strands in DNA. For example, the DNA sequence 5 -CC(1ATT ACG-3 is transcribed into the RNA sequence 3 -GGCUAAUGC-5. (Complementary DNA and RNA sequences are antiparallel.)... 

The mRNA leaves the nucleus and attaches itself to ribosomal ribonucleic acid (rRNA) in the cytoplasm of the cell. Without going into precise detail, rRNA reads the base-sequence code of mRNA and a third type of RNA, transfer ribonucleic acid (tRNA) brings the correct amino acid to the forming protein. This process is known as translation. Each amino acid is coded for by a sequence of three bases, known as a triplet code. For example, ACA codes for the amino acid cysteine. As amino acids are added in sequence a protein is built up. 

The genetic information is contained within the chemical structure of DNA, deoxyribonucleic acid, namely the sequence of bases along the polynucleotide chain. RNA, ribonucleic acid, is used by an organism to act as a messenger between the genes and the site of protein synthesis, the ribosome. The genes of all cells and many viruses are made of DNA. 

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