With the exception of a few viruses, DNA forms the genetic material in all living organisms. In the prokaryotic cells DNA occurs in the cytoplasm. In the eukaryotic cells it is confined largely to the nucleus and forms the main component of chromosomes. A small amount of DNA is found in the cytoplasm in the organelles like mitochondria and plastids. It is called extra- nuclear DNA.
DNA is a polynucleotide of adenine, guanine, cytosine and thymine. Uracil nucleotides are absent. The DNA molecule is composed of two polynucleotide chains.
The structure of the DNA molecule and the arrangement of nitrogenous bases in the two polynucleotide chains, is very well explained by the double helix model proposed by Watson and Crick in 1953.
Watson and Crick
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This shows the synthesis of ethlyene oxide which can be used as a fumigant for foods, textiles, soils and for sterilizing biomedical instruments. It readily diffuses through materials without damanging them. Its antibacterial effect is probably due to its ability to alkylate critical cellular enzymes.
The above reaction is an example of a Williamson synthesis of an ether. It is one the earlier steps in the reaction mechanism resulting in the octaethylene glycol derivative of 1,1,1,3,5,5,5-heptamethyltrisiloxane. Such an initial Williamson synthesis reaction had to be carried out so that later steps in the reaction—that is, ones involving material types not readily accessible—could successfully yield the derivative product. The resultant glycol derivative is an example of a defined surfactant. This particular journal article focused on the correlation between surfactant constituents and the effect on properties such as spreading performance.
The Williamson synthesis involves an SN2 reaction in which a halogen, sulfonyl, or sulfate group is replaced by an alkoxide ion, which can itself be prepared by a reaction of the alcohol with an active metal such as sodium or its hydride (i.e. NaH). The resultant alkoxide salt then reacts with the alkyl halide (must be primary) to produce an ether via the SN2 mechanism.
Other examples of Williamson synthesis of ethers can be found in this same reaction mechanism used to produce the surfactant.
Enzymes are complex biochemical catalysts, speeding up a particular reaction to produce an ordered, stable reaction system in which the products of any reaction are made when they are needed. A specific enzyme controls each reaction in a series of metabolic reactions. Enzymes also control cell metabolism by regulating how and when reactions occur.
They are made up of globular proteins that have complex tertiary or quaternary structure. Enzyme shape is maintained by hydrogen bonds and ionic forces and their function can be affected by changes in temperature and pH.
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This is one of the steps in the synthesis of Taxol. Taxol is an anticancer drug found in the bark of the Pacific yew tree. In the step outlined, an ester is reduced by LiAlH4 and THF to an alcohol.
