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The enzyme RNA polymerase or RNAP is a nucleotidyltransferase that polymerises ribonucleotides in accordance with the information present in DNA. RNA polymerase enzymes are essential and are found in all cells of all organisms. RNAP accomplishes de novo synthesis. It is able to do this because specific interactions with the initiating nucleotide hold RNAP rigidly in place, facilitating chemical attack on the incoming nucleotide. Such specific interactions explain why RNAP prefers to start transcripts with ATP (followed by GTP, UTP, and then CTP).
RNAP was discovered independently by Sam Weiss and Jerard Hurwitz in 1960.
1 RNA polymerase in prokaryotes
In prokaryotes, the same enzyme catalyzes the sythesis of all three types of RNA: mRNA, rRNA and tRNA.
RNAP in E. coli is a relatively huge molecule of about 449 kD. Its core is made of 4 subunits: two α subunits, one β subunit, and one β' subunit. The RNAP holoenzyme consists of α2ββ'σ. The role of the σ subunit is to bind to a specific site of the DNA matrix, called promoter, to start the transcription. The σ subunit is released once the promoter is found. The rest of the enzyme, i.e. α2ββ', is where polymerization takes place. The structure RNAP exhibits a groove with a length of 55 Å and a diameter of 25 Å. This groove fits well the 20 Å double strand of DNA. The 55 Å length can accept 16 nucleotides.
2 RNA polymerase in eukaryotes
EukaryoteEukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. They include the animals, plants, and fungi, which are mostly multicellular, as well as various other groups called protists, many of whichs have several types of RNAP:
- RNA polymerase I synthesizes precursors of rRNA.
- RNA polymerase II synthesizes precursors of mRNA. This is the most studied type, and transcription factorIn molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. Transcription factors can be selectively activated or deactivated by other proteins, often as thes are required for its binding to its promoters.
- RNA polymerase III synthesizes tRNA, rRNA 5S and other small RNA's found in the nucleusIn cell biology, the nucleus is an organelle, found in most eukaryotic cells, which contains most of the cell's genetic material. Nuclei have two primary functions: to control chemical reactions within the cytoplasm and to store information needed for cel and cytosolThe cytosol (as opposed to cytoplasm which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. Proteins within the cytosol play an important role in signal transduction pathways, glycolysis, an.
- Other RNA polymerase types in mitochondria and chloroplastChloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. Chloroplasts are similar to mitochondria but are found only in plants. Both organelles are surrounded by a double membrane with an intermembrane space; bots.
3 Isolation
RNA polymerase can be isolated in the following ways:
- By a phosphocellulose column (PC).
- By glycerol gradient centrifugation (GG).
- By a DNA column (A).
- PC+A
Molecular geneticsMolecular genetics is the field of biology which studies the structure and function of genes at a molecular level. Molecular genetics employs the methods of genetics and molecular biology. It is so-called to differentiate it from other sub fields of genet
RNARNA may also stand for the Republic of New Africa Ribonucleic acid RNA is a nucleic acid consisting of a string of covalently-bound nucleotides. It is biochemically distinguished from DNA by the presence of an additional hydroxyl group, attached to each p
