Chosen for you. RNA Polymerase. DNA Polymerase. Transcription of DNA. Replication of DNA. To make RNA copies of genes. To copy the entire genome. Time of occurrence. Used in transcription during G phase s. Used in replication during S phase. Not required for transcription. Required for initiation of replication.
Base pairs used to synthesize product. Adenine, Guanine, Cytosine and Uracil. Adenine, Guanine, Cytosine and Thymine.
The process of DNA replication is shown in figure 1. All three types of RNA are involved in the protein synthesis. The binding of the RNA polymerase requires the identification of the promoter of the gene, which is going to be transcribed. The process of transcription is shown in figure 2. Prokaryotes contain a single RNA polymerase type. It also polymerizes rRNA. DNA Polymerase: E. In turn, transcript elongation leads to clearing of the promoter, and the transcription process can begin yet again.
Transcription can thus be regulated at two levels: the promoter level cis regulation and the polymerase level trans regulation.
These elements differ among bacteria and eukaryotes. In bacteria, all transcription is performed by a single type of RNA polymerase. This polymerase contains four catalytic subunits and a single regulatory subunit known as sigma s. Interestingly, several distinct sigma factors have been identified, and each of these oversees transcription of a unique set of genes.
Sigma factors are thus discriminatory, as each binds a distinct set of promoter sequences. A striking example of the specialization of sigma factors for different gene promoters is provided by bacterial sporulation in the species Bacillus subtilis. This bacterium exists in two states: vegetative growing and sporulating. Genes involved in spore formation are not normally expressed during vegetative growth.
Remarkably, expression of a gene encoding a novel sigma factor turns on the first genes for sporulation. Each of these sigma factors recognizes the promoters of the genes in its group, not those "seen" by other sigma factors. This simple example illustrates how transcription can be regulated in both cis and trans to cause changes in cell function. Therefore, while bacteria accomplish transcription of all genes using a single kind of RNA polymerase, the use of different sigma factor subunits provides an extra level of control.
Interestingly, RNA pol II is uniquely sensitive to amatoxins, such as a-amanitin of the extremely toxic Amanita genus of mushrooms Weiland, , a fact that researchers have been able to exploit for the purposes of polymerase studies - although recreational mushroom hunters should beware!
Thus, while eukaryotic transcription is far more complex than bacterial transcription, the main difference between the two types of transcription lies in RNA polymerase. Hahn, S. Nature Structural and Molecular Biology 11 , — link to article. Losick, R. Crisscross regulation of cell-type-specific gene expression during development in B. Nature , — doi Atavism: Embryology, Development and Evolution. Gene Interaction and Disease. Genetic Control of Aging and Life Span. Genetic Imprinting and X Inactivation.
Genetic Regulation of Cancer. Obesity, Epigenetics, and Gene Regulation. Environmental Influences on Gene Expression. Gene Expression Regulates Cell Differentiation. Genes, Smoking, and Lung Cancer. Negative Transcription Regulation in Prokaryotes. Operons and Prokaryotic Gene Regulation. Regulation of Transcription and Gene Expression in Eukaryotes. The Role of Methylation in Gene Expression. DNA Transcription. Reading the Genetic Code.
Simultaneous Gene Transcription and Translation in Bacteria.
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