DNA-directed protein synthesis

DNA directing Protein Synthesis in a Cell The DNA directed protein synthesis occurs in two steps—... 

Although more than 700 different amino acids are known to occur naturally, the group of 20 called the standard amino acids listed in Table 25.1 (pages 1120-1121) commands special attention. These 20 are the amino acids coded for in DNA-directed protein synthesis. All are a-amino acids, and all but one contain a primary amino function. 

Fig. 14. Kinetics of synthesis of 29 lysozyme in vitro. The reaction mixtures for 29 DNA directed protein synthesis were incubated in the presence of either 11 or 16 mM Mg2+. Aliquots were removed at various times (as indicated) and kept on ice with 50 (xg/ml...

Translation (Section 28.5) The process by which the genetic information transcribed from DNA onto mRNA is read by tRNA and used to direct protein synthesis. 

The flow of biological genome knowledge is from DNA to RNA via transcription, and from RNA to direct protein synthesis via translation. 

Plicamycin is a cytotoxic antibiotic (see Chapter 54) that has been used clinically for two disorders of bone mineral metabolism Paget s disease and hypercalcemia. The cytotoxic properties of the drug appear to involve its binding to DNA and interruption of DNA directed RNA synthesis. The reasons for its usefulness in the treatment of Paget s disease and hypercalcemia are unclear but may relate to the need for protein synthesis to sustain bone resorption. The doses required to treat Paget s disease and hypercalcemia are about one tenth the amounts required to achieve cytotoxic effects. 

It is well established that actinomycin D inhibits DNA-directed RNA synthesis by binding to guanosyl residues in the DNA molecule. This disrupts the transcription of genetic information and thereby interferes with the production of essential proteins. DNA synthesis may also be inhibited, being reduced by 30% to 40% in utero. It is clear that in the initial stages of embryogenesis, synthesis of RNA for protein production is vital, and it is not surprising that inhibition of this process may be lethal. 

Three processes take place in the transfer of genetic information Replication is the process by which identical copies of DNA are made and genetic information is preserved. Transcription is the process by which messenger RNA is produced. Translation is the process by which mRNA directs protein synthesis. 

RNA molecules are typically much smaller than DNA, and they are more easily hydrolyzed and broken down. RNA commonly serves as a working copy of the nuclear DNA being decoded. Nuclear DNA directs the synthesis of messenger RNA, which leaves the nucleus to serve as a template for the construction of protein molecules in the ribosomes. After it has served its purpose, the messenger RNA is then enzymatically cleaved to its component parts, which become available for assembly into new RNA molecules to direct other syntheses. 

Direct measurement of DNA and protein synthesis in experimental animals suggest that in zinc deficiency protein synthesis is adversely affected (, ). Our own data on human subjects in these experiments show that the total protein, total collagen, and RNA-DNA ratio Increased as a result of zinc supplementation. The activity of deoxythymidine kinase was not measurable during the zinc restriction phase but became 70% of normal level after supplementation with zinc for 3 months. Similar data have been published for experimental animals. Thus, our data show that deoxythymidine kinase in human subjects also is a zinc-dependent enzyme, and an adverse effect of zinc deficiency on this enzyme may be responsible for decreased protein synthesis. Our studies do not rule out an adverse effect of zinc deficiency on protein catabolism. Further studies are required to establish the effect of zinc restriction on protein catabolism. 

Figure 1 The central dogma of molecular biology. The central dogma describes the flow of information between the principle biopolymers of the cell. The primary exchange is shown horizontally, left to right, namely, DNA directs the synthesis of RNA, which in turn directs the synthesis of protein. Alternate observed exchanges are depicted off the horizontal with less prominent lines. The letters "P" and "R" indicate that protein or RNA, respectively, are required for particular exchanges.

Biochemists refer to RNA synthesis as transcription. Transcription is the process of synthesizing ribonncleic acid (RNA). Synthesis takes place within the nnclens of eukaryotic cells or in the cytoplasm of prokaryotes and converts the genetic code from a gene in deoxyribonucleic acid (DNA) to a strand of RNA that then directs protein synthesis. 

In this paper, we have summarized our current understanding of the biochemical nature of the triazine binding site within the PS II complex. Studies using the proteolytic enzyme trypsin as a selective, surface-specific modifier of membrane polypeptides and the use of a photoaffinity triazine have been utilized separately to identify the triazine receptor protein as a 32-34 kilodalton (kDal) polypeptide of the PS II complex in peas (Pisum sativum L.). The nature of the covalent attachment of the photoaffinity probe has also enabled us to identify the triazine receptor protein as a product of chloroplast-directed protein synthesis this implies that the structural gene for the triazine receptor polypeptide is encoded on chloroplast DNA. 

Metabolic disruptions may result in inhibition of cell enlargement. Key (9) found that actinomycin D, an inhibitor of DNA directed RNA synthesis (10), and puromycin, an inhibitor of protein synthesis, will prevent cell enlargement in soybean Glycine max L. Merr.) hypocotyls. Key concluded RNA and protein synthesis are essential for the process of cell elongation to proceed at a normal rate. The following year, Cleland reported the inhibition of cell enlargement caused by actinomycin D was not caused by an inhibition of auxin-induced cell wall loosening... 

Ribonucleic acids (RNAs) Nucieic acids that transmit genetic information and direct protein synthesis contain ribose Nucleotide Biomolecule with a five-carbon sugar bonded to a nucleic acid base and a phosphate group monomer in DNA... 

Messenger RNA (m-RNA) was discovered by Brenner in 1960. It carries genetic messages from DNA to the ribosomes, where directed protein synthesis takes place. 

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