Primed synthesis examples

Covalent synthesis of complex molecules involves the reactive assembly of many atoms into subunits with aid of reagents and estabUshed as well as innovative reaction pathways. These subunits are then subjected to various reactions that will assemble the target molecule. These reaction schemes involve the protection of certain sensitive parts of the molecule while other parts are being reacted. Very complex molecules can be synthesized in this manner. A prime example of the success of this approach is the total synthesis of palytoxin, a poisonous substance found in marine soft corals (35). Other complex molecules synthesized by sequential addition of atoms and blocks of atoms include vitamin potentially anticancer KH-1 adenocarcinoma antigen,... 

As we began this chapter, we saw that photosynthesis traditionally is equated with the process of COg fixation, that is, the net synthesis of carbohydrate from COg. Indeed, the capacity to perform net accumulation of carbohydrate from COg distinguishes the phototrophic (and autotrophic) organisms from het-erotrophs. Although animals possess enzymes capable of linking COg to organic acceptors, they cannot achieve a net accumulation of organic material by these reactions. For example, fatty acid biosynthesis is primed by covalent attachment of COg to acetyl-CoA to form malonyl-CoA (Chapter 25). Nevertheless, this fixed COg is liberated in the very next reaction, so no net COg incorporation occurs. 

The plant of choice which can be used for PHA production will be influenced by a number of factors. Of prime importance is cost, i. e., in which crop will PHA production be cheapest. The answer to this question is likely to be different depending on the agricultural economics of each country. For example, if one considers oilseed crops, rapeseed may be the best crop for Northern European countries and Canada, sunflower for Southern European countries, and soybean for the USA. Other important factors which may influence the choice of target plant are the nature of the metabolic pathway that needs to modified for synthesis of a particular PHA, the procedure used for PHA purification, and the other uses of the crop besides PHA production. 

Solid-phase synthesis of biomolecules, of which peptides are the prime example, is well established. The search for more effective therapeutic agents creates a need for different strategies to synthesize peptides with C-terminal end groups other than the usual carboxylic acid and carboxamide functionalities. Methods described herein are readily generalized to small nitrogen-containing organic molecules. 

Figure 4.26 (a) DNA replication at low resolution (for example as seen by electron microscopy). Only one replication fork is visible and it appears that both strands of the parental DNA replicate continuously in the same direction, which cannot be the case, since the two strands of parental DNA are anti-parallel, (b) The problem is solved by the priming of DNA synthesis with short RNA primers, whose 3 -hydroxyl can be used by DNA polymerase, producing Okazaki fragments, while on the other strand, DNA synthesis is continuous. (From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc.)... 

A prime example of these features can be found in the synthesis of styrene/ (meth)acrylate random copolymers. By controlling the initiator/total monomer ratio, the molecular weight can be accurately controlled for both styrene/methyl methacrylate and styrene/butyl acrylate random copolymers. As can be seen in Figure 2.3 the polydispersity for both systems is essentially 1.10-1.25 over comonomer ratios ranging from 1/9 to 9/1. 

Copolymerization allows the synthesis of an almost unlimited number of different products by variations in the nature and relative amounts of the two monomer units in the copolymer product. A prime example of the versatility of the copolymerization process is the case of polystyrene. More than 11 billion pounds per year of polystyrene products are produced annually in the United States. Only about one-third of the total is styrene homopolymer. Polystyrene is a brittle plastic with low impact strength and low solvent resistance (Sec. 3-14b). Copolymerization as well as blending greatly increase the usefulness of polystyrene. Styrene copolymers and blends of copolymers are useful not only as plastics but also as elastomers. Thus copolymerization of styrene with acrylonitrile leads to increased impact and solvent resistance, while copolymerization with 1,3-butadiene leads to elastomeric properties. Combinations of styrene, acrylonitrile, and 1,3-butadiene improve all three properties simultaneously. This and other technological applications of copolymerization are discussed further in Sec. 6-8. 

This reaction is important for a number of reasons. It is an industrial synthesis of aldehydes from alkenes by the addition of carbon monoxide and hydrogen in the presence of a cobalt catalyst. A prime example is the synthesis... 

The end of a linear chromosome is called a telomere. Telomeres require a special mechanism, because the ends of a linear chromosome can t be replicated by the standard DNA polymerases. Replication requires both a template and a primer at whose 3 end synthesis begins. The primer can t be copied by the polymerase it primes. What copies the DNA complementary to the primer In a circular chromosome, the primer site is to the 3 direction of another polymerase, but in a linear chromosome, no place exists for that polymerase to bind. As a result, unless a special mechanism for copying the ends of chromosomes is used, there will be a progressive loss of information from the end of the linear chromosome. Two characteristics about telomeres help avoid this situation. First, they consist of a short sequence—for example, AGGGTT—repeated many times at the end of each chromosome. Telomeres, therefore, are part of the highly repetitive DNA complement of a eukaryotic cell. Secondly, a specific enzyme, telomerase, carries out the synthesis of this reiterated DNA. Telomerase contains a small RNA subunit that provides the template for the sequence of the telomeric DNA. Eukaryotic somatic cells have a lifespan of only about 50 doublings, unless they are cancerous. One theory holds that a lack of telomerase in cells outside the germ line causes this limitation. 

LPS has been found not only to induce defense responses directly but also to promote or prime an early triggering of defense responses upon subsequent bacterial inoculation. An example of this is the LPS priming of the synthesis of the antimicrobial compounds feruloyl tyramine (FT) and p-coumaroyl tyramine (CT) in pepper plants (Newman et al., 2001, 2002 Prime-A-Plant Group, 2006). LPS treatment of pepper leaves does not lead to synthesis of FT and CT. However, these compounds are synthesized more rapidly upon bacterial inoculation into LPS pre-treated than water pre-treated plants (Newman et al., 2001, 2002 Prime-A-Plant Group, 2006). 

Ferrioxamines B and E are prime examples of the linear and cyclic species, respectively. Several members of the series have been prepared by total synthesis, thus establishing the sequence of the contained units (For example, four isomers could be constructed from the hydrolytic products of ferrioxamine B). The three hydroxamate functions must be spatially located so as to form a stable, intramolecular hexa-dentate ferric chelate. Acetylation of ferrioxamine B affords ferrioxa-mine Di ferrioxamine G corresponds to component B with succinic replacing acetic acid cyclization of G yields ferrioxamine E components Ai and D2 carry l-amino-4-hydroxyaminobutane in place of a residue of the next higher homologue. 

Methods for the isolation of both total RNA and mRNA20 and the synthesis of first-strand cDNA21 are not described here. For this method, cDNA synthesis must be primed with oligo(dT) because this is also used as one of the amplification primers. Examples of products of the amplification of cDNA are shown in Fig. 2. 

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