Biochemistry of Nutrition Assignment Example | Topics and Well Written Essays - 500 words

Biochemistry of Nutrition - Assignment Example The mechanisms included in DNA tolerance are a replicative bypass of template damage with gap formation and translesion DNA synthesis. This paper attempts to throw light on DNA repair by direct repair mechanisms. The major source of base damage upon exposure to UV radiation at wavelengths near absorption maximum of DNA is the production of photo products such as cyclobutane pyrimidine dimers and 6-4 pyrimidine-pyrimidones. The photoproducts mediate DNA damage by posing serious threats to viability and functional integrity of cells by interfering with vital processes including DNA replication and transcription. The reversal of DNA damage through photoreactivation is a mechanism that involves the repair of photoproducts. The light-dependent process reverses DNA damage through monomerization of cis-syn-cyclobutyl pyrimidine dimers. Furthermore, the trans-syn-cyclobutyl pyrimidine is also repaired through the light-dependent repair process. The process involves the formation of a DNA complex with photoreactivating enzyme. The complex absorbs light (>300nm) which causes the repair of the damaging photoproducts after which the native DNA is restored after the release of photoreactivating enzyme. The depletion of one or more nutrients results in sporulation in Bacillus subtilis. A spore product called thyminyl-thymine adduct is formed when Bacillus subtilis is exposed to UV radiation at ~240nm. The repair of spore photoproduct occurs during early germination and is mediated through the SP-specific repair process. Furthermore, spore photoproducts are also repaired through nucleotide excision repair system. The formation of O6-Methylguanine occurs as a result of damage caused by the presence of alkylating agents such as N-methyl-N-nitrosoguanidine.

Recommendation of process routes for the sepration of LPG Essay

Recommendation of process routes for the sepration of LPG - Essay Example To separate these two constituents, several processes can be used. This method involves the recovery and increase in the purity of the light hydrocarbons butane and propane from their mixture in liquid petroleum gas. It is based on the distillation of the gas by controlled heating and cooling, by taking gain of the diverse boiling points of the hydrocarbons. Fractionating columns are used with labels if the hydrocarbon is separated by evaporation. Liquid petroleum gas composition of propane and butane which makes up to 40% natural gas is extracted as a liquid mixture in a fractionating column (Zlokarnik, 2002). After its extraction from natural gas, the refrigerated liquid petroleum gas is passed through an absorber column where it is mixed with lean oil at a temperature of 238 degrees Celsius to allow for the absorption of the liquid petroleum gas products. This process is accelerated by elevated pressure and low temperature and the refrigeration of the liquid petroleum gas is ensured by using a closed loop circulation of a refrigerant in centrifugal compressors. The liquid petroleum gas is precooled before it enters a de-ethanizer column with a pressure lower than the pressure of the liquid petroleum gas. In the de-ethanizer, ethane and other lighter components in the liquid petroleum gas are removed. A constant temperature is maintained in the column by using a reboiler placed at the bottom of the fractionating column to supply heat. The overhead vapour is recycled to recover any escaped propane from the evaporated gas. The residue is then passed through a rich oil still column where th e lean oil is separated using distillation. The liquid petroleum gas that is separated is condensed in a reflux condenser and is then directed into fractionating columns. Depropanizer and debutanizer systems are used to separate the stabilized