Ribonucleic Acid RNA synthesis

Rifaximin is a synthetic rifamycin derivative, which acts by inhibiting bacterial ribonucleic acid (RNA) synthesis [48]. It is virtually unabsorbed after oral administration and is, therefore, used primarily to treat gastrointestinal infections. Rifaximin possesses a broad spectrum of antimicrobial activity, covering Gram-positive and Gram-negative bacteria, both arerobic and anaerobic [49], Several studies [44, 49-62] have shown that in patients with HE rifaximin displays an efficacy similar to that of lactulose and neomycin (table 1). A recently published study [62] compared the efficacy and safety of... 

Another mode of protein-electric field interaction has been proposed by Blank (18-21). Blank considers that the effects of an electric field on membrane protein mainly arise from its effect on the electric double layer at the water-membrane interface. In other words, an electric field can change the concentration of ions near a membrane protein, which results in a stimulation or a reduction in its activity. The surface compartmental model has been used to interpret the ac stimulated adenosine triphosphate (ATP) splitting of Na, K-ATPase (adenosine triphosphatase) and ribonucleic acid (RNA) synthesis in various types of cells (19-21). 

Substantial inhibition of ribonucleic acid (RNA) synthesis (86% inhibition) by trichothecene myco-toxin was observed in human (HeLa) cells,47 but T-2 toxin had minor effects (15% inhibition) on RNA synthesis in Vero cells.46 The trichothecene myco-toxin-related inhibition of RNA synthesis is probably a secondary effect of the inhibition of protein synthesis. Scheduled DNA synthesis is strongly inhibited in various types of cells that are exposed to trichothecene mycotoxins. In mice or rats treated with trichothecene mycotoxins, DNA synthesis in all tissues studied was suppressed, although to a lesser degree than protein synthesis.49 The pattern by which DNA synthesis is inhibited by the trichothecene mycotoxins is consistent with the primary effect of these toxins on protein synthesis. In appropriate cell models, for the most part, trichothecene mycotoxins demonstrate neither mutagenic activity nor the capacity to damage DNA.50... 

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... 

Ribonucleic acid (RNA) (Section 28.1) The biopolymer found in cells that serves to transcribe the genetic information found in DNA and uses that information to direct the synthesis of proteins. 

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. 

Ribonucleic acid (RNA) Molecules including messenger RNA, transfer RNA, ribosomal RNA, or small RNA. RNA serves as a template for protein synthesis and other biochemical processes of the cell. The structure of RNA is similar to that of DNA except for the base thymidine being replaced by uracil. 

The initial conversion of light into chemical energy takes place in the thylakoid membrane. Besides the chlorophylls and series of electron carriers, the thylakoid membrane also contains the enzyme adenosine triphosphate (ATP) synthase. The enzymes that are responsible for the actual fixation of C02 and the synthesis of carbohydrate reside in the stroma that surround the thylakoid membrane. The stroma also contains deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and ribosomes that are essential for protein synthesis [37]. 

All cells in living organisms contain the large nucleic acid molecules of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Both these molecules are polymers of nucleotides. DNA is found in chromosomes, and genes are unique sequences of DNA nucleotides. The genes contain the inheritable information which together with RNA directs the synthesis of all the cell s proteins. 

Deoxyribonucleic acid (DNA) serves as a template for the synthesis of nucleic acids. Ribonucleic acid (RNA) executes protein synthesis and thus permits cell growth. Synthesis of new DNA is a prerequisite for cell division. Substances that inhibit reading of genetic information at the DNA template damage the regulatory center of cell metabolism. The substances listed below are useful as antibacterial drugs because they do not affect human cells. 

The fluoropyrimidines as a group can affect the synthesis and function of both deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), and both of these two mechanisms... 

It is clear that DNA does not play a direct role in the synthesis of proteins and enzymes because most of the protein synthesis takes place outside of the cell nucleus in the cellular cytoplasm, which does not contain DNA. Furthermore, it has been shown that protein synthesis can occur in the absence of a cell nucleus or, equally, in the absence of DNA. Therefore the genetic code in DNA must be passed on selectively to other substances that carry information from the nucleus to the sites of protein synthesis in the cytoplasm. These other substances are ribonucleic acids (RNA), which are polymeric molecules similar in structure to DNA, except that D-2-deoxyribofuranose is replaced by... 

In the case of neuropeptides, presynaptic neurotransmission synthesis occurs only in the cell body because the complex machinery for neuropeptide synthesis is not transported into the axon terminal. Synthesis of a specific neuropeptide begins with the pre-propeptide gene in the cell nucleus (Fig. 1 —9). This gene is transcribed into primary ribonucleic acid (RNA), which can be rearranged, or edited, to create different versions of RNA, known as alternative splice variants, such as prepropeptide RNA. 

To understand the biochemistry of mutagenesis, it is important to recall from Chapter 3 that DNA contains the nitrogenous bases adenine, guanine, cytosine, and thymine. The order in which these bases occur in DNA determines the nature and structure of newly produced ribonucleic acid (RNA), a substance produced as a step in the synthesis of new proteins and enzymes in cells. Exchange, addition, or deletion of any of the nitrogenous bases in DNA alters the nature of RNA produced and can change vital life processes, such as the synthesis of an important enzyme. This phenomenon, which can be caused by xenobiotic compounds, is a mutation that can be passed on to progeny, usually with detrimental results. 

In vitro genotoxicity studies are summarized in Table 2-17. Eukaryotic cell systems were used for detecting the effects of 2,3,7,8-TCDD exposure on DNA. Exposure to 2,3,7,8-TCDD did not stimulate the unscheduled DNA synthesis in cultural human cells (Loprieno et al. 1982), but inhibited DNA, ribonucleic acid (RNA), and protein synthesis in mouse lymphocytes (Luster et al. 1979) caused gene mutations in mouse lymphoma cells (Rogers et al. 1982) and induced sister chromatid exchanges in Chinese hamster cells (Toth et al. 1984). 

The nucleus of eukaryotic cells is a very complex structure, containing various components. It is separated from the rest of the cell by two membranes named the nuclear envelope. At regular intervals, the two membranes of the nuclear envelope form pores with a diameter of around 90 nm. These pores regulate flux of macromolecules to and from the cytoplasm. Inside the nucleus is located the nucleolus, which acts to produce ribonucleic acid (RNA), which is the first step for ribosome synthesis. 

The nucleus of the cell (Figure 1.2) is composed of a porous nuclear membrane, the nucleolus, and soluble materials. The nucleolus contains ribonucleic acids (RNA) and genetic materials also termed chromatin that code for the proteins synthesized upon the ribosomes in the cell cytoplasm. The nuclear membrane is continuous with the outer membrane of the endoplasmic reticulum. Messenger RNA synthesized in the nucleus is transported across the nuclear membrane and is involved in protein synthesis. It fits into the groove between the large and small rRNA subunits (Figure 1.2)... 

Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) are both biopolymers of nucleic acids, but they have minor structural differences that lead to major functional differences. All living cells use DNA as the primary genetic material that is passed from one generation to another. DNA directs and controls the synthesis of RNA, which serves as a short-lived copy of part of the much larger DNA molecule. Then, the cellular machinery translates the nucleotide sequence of the RNA molecule into a sequence of amino acids needed to make a protein. 

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