Deoxyribonucleic acid enzymic synthesis

As the name suggests, cyanocobalamin (vitamin B12) is a compound of cobalt (Co(lll)). With a complex organic structure, this essential water-soluble vitamin is obtained from dietary animal sources and is required for deoxyribonucleic acid (DNA) synthesis, where enzymes that use vitamin B12 are involved in the transfer of one-carbon units. The absorption of this vitamin from the gastrointestinal tract only occurs when intrinsic factor glycoprotein is present. While the body can store up to a 12-month supply of vitamin B12, rapid growth or conditions causing rapid cell turnover can increase the body s requirement for this vitamin. 

Chamberlin, M. and Berg P. (1962) Deoxyribonucleic acid-directed synthesis of ribonucleic acid by an enzyme from Escherichia coli. Proc. Nat. Acad. Sci. 48, 81. 

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... 

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]. 

Physiologically, this vitamin, after absorption, which takes place throughout most of the small bowel, is inextricably linked to its co-enzyme vitamin B12 and they share a final common pathway culminating in the optimum synthesis of deoxyribonucleic acid. 

M. J. Bessman, J. R. Lehman, J. Adler, S. B. Zimmerman, E. S. Simms, and A. Komberg, Enzymic synthesis of deoxyribonucleic acid. III. Incorporation of pyrimidine and purine analogs into deoxyribonucleic acid, Proc. Natl. Acad. Sci. USA 44 633 (1958). 

Deoxyribonucleic acid (DNA) belongs to a group of chemicals called the nucleic acids (Figure 15.26) They are also biopolymers. DNA controls the prote synthesis within your cells. When you eat a food containing proteins, such as meat or cheese, your digestive enzymes break down the proteins present into individual amino acids. The DNA in your cells controls the order in which the amino acids are repolymerised to make the proteins you need ... 

Fundamental knowledge of the structure, function and mechanism of DNA-modifying enzymes has been important not only in understanding how these enzymes perform a myriad of chemical reactions Ml vZvo but also for the development of the field of recombinant DNA technology. The functions of the major groups of enzymes in deoxyribonucleic acid synthesis, hydrolysis and modification are reviewed, as well as some structural and mechanistic aspects of the restriction endonucleases, ligases and polymerases. 

The hereditary material of the cell consists of deoxyribonucleic acid (DNA). DNA is similar to RNA, but the five carbon sugar, deoxyribose replaces ribose, and in place of uracil, the base thymine is found. DNA occurs as a double-stranded molecule. The two strands are held together by hydrogen bonds. DNA polymerase is one of the enzymes responsible for the process of replication whereby the double strands are separated and used as a template for the synthesis of new strands. Replication precedes cell division so that each new cell receives its own complement of double-stranded DNA. 

The carbohydrate component of ribonucleic acid and, therefore, of the corresponding purine nucleosides was identified as a pentose by Hammar-sten and, later, as D-ribose by degradation and then by synthesis. Because of the instability of 2-deoxy-D-erythro-peutose ( 2-deoxy-D-ribose ), its isolation from deoxyribonucleic acid was much more difficult. Levene and coworkers finally obtained the crystalline sugar from deoxyguanosine by brief treatment with dilute mineral acid. They established its identity by comparison with synthetic 2-deoxy-D-threo-pentose and 2-deoxy-L-er /[Pg.303]

As shown by Komberg and coworkers, infection of Escherichia coli by these bacteriophages triggers the synthesis of new enzymes, including D-glucosyl transferases, which had been totally lacking before infection these enzymes catalyze the synthesis of the type of deoxyribonucleic acid characteristic of that phage. 

Nitrogen is the one element above all others that we associate with growth. As pointed out in Chapter 14, it is a constituent of proteins, enzymes, chlorophyll, deoxyribonucleic acids that make up the genetic code, amino acids and many intermediates invplved in the synthesis of plant substances. It is characteristically present in comparatively large amounts in the growing tips of plants, hut it can move about readily from one part of the plant to another to meet the primary needs at the time. 

The antimetabolite, raltitrexed, is a folate analogue and is a potent and specific inhibitor of the enzyme thymidylate synthase. Inhibition of this enzyme ultimately interferes with the synthesis of deoxyribonucleic acid (DNA) leading to cell death. The intracellular polyglutamation of raltitrexed leads to the formation within cells of even more potent inhibitors of thymidylate synthase. Folate (methylene tetrahydrofolate) is a co-faetor required by thymidylate synthase and therefore theoretically folinic acid or folic acid may interfere with the aetion of raltitrexed. Clinieal interaction studies have not yet been undertaken to confirm these predieted inter-aetions. ... 

E.S. and Kornberg, (1958) A. Enzymatic synthesis of deoxyribonucleic acid. I. Preparation of substrates and partial purification of an enzyme from Escherichia coli. / Bid. Chem., 233, 163-170. 

Richardson, C. C.., R. B. Inman, and A. Kornberg. 1964. Enzymic synthesis of deoxyribonucleic acid. XVIII. The repair of partially single-stranded DNA templates by DNA polymerase. J. Molec. Biol., 9 46-69. 

The directed synthesis of deoxyribonucleic acid (DNA) and its manipulation for genetic engineering would be impossible without enzyme catalysis. There is a range of restriction enzymes which can break DNA strands at specific points defined by the local base sequence, as well as ligases which can rejoin the broken ends where new base sequences are inserted, and they are essential catalysts. They complement the chemical synthesis of the oligonucleotides (small segments of DNA) which are inserted. A discussion of the technique is outside the scope of this chapter, largely because the... 

The information which specifies the amino-acid sequence of a protein is stored in the nucleotide sequence of the double helix of deoxyribonucleic acid (DNA). The transcription of sections of this information into ribonucleic acid (RNA) is catalysed by RNA polymerases. These enzymes not only control the synthesis of RNA but also recognize stop and start signals on the DNA. The start signals are complex and may be blocked by repressor molecules which inhibit the transcription process. Once synthesized, the (messenger) RNA is processed and exported to ribosomes where its nucleotide sequence is translated into protein. Triplets of three nucleotides (codons) in the messenger RNA each specify (encode) one amino acid. The linear sequence of nucleotides in the messenger RNA thus specifies the sequence of amino acids in the protein whose primary structure will therefore correspond directly to the sequence of nucleotides in the DNA. 

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