explain the role of the nucleolus in protein synthesis.
Dietary habits have an important influence on susceptibility to chemical toxicity, mostly because adequate nutrition is essential for the functioning of the bodys chemical defence system in maintaining good health. Adequate intake of essential metals (including metalloids) and proteins, especially the sulphur-containing amino acids, is necessary for the biosynthesis of various detoxificating enzymes and the provision of glycine and glutathione for conjugation reactions with endogenous and exogenous compounds. Lipids, especially phospholipids, and lipotropes (methyl group donors) are necessary for the synthesis of biological membranes. Carbohydrates provide the energy required for various detoxification processes and provide glucuronic acid for conjugation of toxic chemicals and their metabolites. Selenium (an essential metalloid), glutathione, and vitamins such as vitamin C (water soluble), vitamin E and vitamin A (lipid soluble), have an important role as antioxidants (e.g., in controlling lipid peroxidation and maintaining integrity of cellular membranes) and free-radical scavengers for protection against toxic chemicals.
the role of rRNA in protein synthesis ..
Other exposures may induce the synthesis of a protective protein in the body. The best example is probably metallothionein, which binds cadmium and promotes the excretion of this metal; cadmium exposure is one of the factors that result in increased expression of the metallothionein gene. Similar protective proteins may exist but have not yet been explored sufficiently to become accepted as biomarkers. Among the candidates for possible use as biomarkers are the so-called stress proteins, originally referred to as heat shock proteins. These proteins are generated by a range of different organisms in response to a variety of adverse exposures.
The preponderance of experimental evidence indicates that the development of cancer following exposure to electrophilic compounds is a relatively rare event. This can be explained, in part, by the cells intrinsic ability to recognize and repair damaged DNA or the failure of cells with damaged DNA to survive. During repair, the damaged base, nucleotide or short stretch of nucleotides surrounding the damage site is removed and (using the opposite strand as a template) a new piece of DNA is synthesized and spliced into place. To be effective, DNA repair must occur with great accuracy prior to cell division, before opportunities for the propagation of mutation.