Regulation of DNA and RNA Synthesis

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Metabolic Regulation Regulation of Enzyme Synthesis Catabolite Repression Enzyme With Repressor Function Attenuation

Regulation of DNA and RNA Synthesis

	Regulation of DNA and RNA Synthesis - The regulation of DNA synthesis under normal conditions is very precise since at cell division each daughter cell must contain a full, complement of the genetic material. Normally, DNA synthesis and cell division are interconnected. However, under certain conditions it is possible to delink these events from one another. In E.coli, the average time required for doubling of DNA is about 40 minutes at 37°C; however, if the organism is grown In a medium in which the time for cell division is longer than 40 minutes, DNA ,synthesis occurs in 40 minutes and a period during which no DNA synthesis occurs is seen.
On the other hand, under conditions where the division is rapid and occurs in less than 40 minutes the replication of DNA also occurs rapidly and a cell may contain DNA equivalent to as much as 3-4 genomes. Under such condition,cells contain DNA with multiple points of synthesis. This situation returns to normal (one point of synthesis) when the cells are transferred to a condition that will permit a division time of 40 minutes or greater. Thus the amount of DNA per cell is regulated by the rate at which organisms grow
The process of DNA synthesis involves initiation, elongation and termination of polynucleotide chain synthesis. Of these three steps the most important step which determines the rate of DNA replication is initiation. Broadly, initiation of DNA synthesis is dependent on protein synthesis and this has led to the hypothesis that initiation of DNA synthesis is under the positive control of a regulatory protein called as initiatorWhen the concentration of the initiator increases, replication begins and once replication is initiated, its completion is not dependant on the continued synthesis of proteins.
Thus, the system operates in a way similar to a pipette washer where in wash out occurs only when the water level has reached a certain critical point.The replication of DNA however, involves the synthesis of a variety of proteins and it is likely that the regulation of DNA synthesis also lies at the regulation of activity and synthesis of these various proteins
	The regulation of RNA synthesis appears to involve a different mechanism depending on the type of RNA being synthesized. The synthesis of m-RNA is regulated at the transcriptional level and the process of induction and repression as described above occurs at this level. The regulation of synthesis of the stable RNA species such as r-RNA and t-RNA is not still completely understood. The rates of synthesis of these molecules can be varied with growth rates, which in turn depend on the composition of the medium. It is known that the rate of RNA synthesis depends on the number of RNA polymerase molecules actively engaged in polymerization; on the other hand, protein synthesis is dependent on RNA synthesis.

Thus in amino acid requiring mutants of E. coli deprived of a required amino acid both protein and RNA synthesis stops. As in DNA synthesis, RNA synthesis is also clearly controlled by the same regulatory mechanisms that govern protein synthesis. Highly phossphorylated nucleotides (HPN) such as tetra or penta, guanine and adenine nucleotides have been found to be involved in the regulation of r-RNA synthesis. It appears that the concentration of these highly phosphorylated nucleotides determines the rate of synthesis of r-RNA.

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Regualtion of Enzyme Activity Other Mechanisms Regulatory Mechanisms in Microorganisms Regulation of DNA and RNA Sysnthesis

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