where does rna polymerase initiate synthesis of mrna
RNA polymerase Eukaryotes have multiple types of nuclear RNAP, each responsible for synthesis of a distinct subset of RNA. All are structurally and mechanistically related to each other and to bacterial RNAP. RNA polymerase I synthesizes a pre-rRNA 45S (35S in yeast). which matures and will form the major RNA sections of the ribosome. RNA polymerase II synthesizes precursors of mRNAs and most snRNA and microRNAs.RNA polymerase III synthesizes tRNAs, rRNA 5S and other small RNAs found in the nucleus and cytosol. RNA polymerase IV synthesizes siRNA in plants. RNA polymerase V synthesizes RNAs involved in siRNA-directed heterochromatin formation in plants. Eukaryotic chloroplasts contain an RNAP very highly structurally and mechanistically similar to bacterial RNAP ("plastid-encoded polymerase"). They also contain a second, structurally and mechanistically unrelated, RNAP ("nucleus-encoded polymerase"; member of the "single-subunit RNAP" protein family). Eukaryotic mitochondria contain a structurally and mechanistically unrelated RNAP (member of the "single-subunit RNAP" protein family).
Okazaki fragments Primase adds RNA primers onto the lagging strand, which allows synthesis of Okazaki fragments from 5' to 3'. However, primase creates RNA primers at a much lower rate than that at which DNA polymerase synthesizes DNA on the leading strand. DNA polymerase on the lagging strand also has to be continually recycled to construct Okazaki fragments following RNA primers. This makes the speed of lagging strand synthesis much lower than that of the leading strand. To solve this, primase acts as a temporary stop signal, briefly halting the progression of the replication fork during DNA replication. This molecular process prevents the leading strand from overtaking the lagging strand.[12]
Protein biosynthesis In protein synthesis, a succession of tRNA molecules charged with appropriate amino acids are brought together with an mRNA molecule and matched up by base-pairing through the anti-codons of the tRNA with successive codons of the mRNA. The amino acids are then linked together to extend the growing protein chain, and the tRNAs, no longer carrying amino acids, are released. This whole complex of processes is carried out by the ribosome, formed of two main chains of RNA, called ribosomal RNA (rRNA), and more than 50 different proteins. The ribosome latches onto the end of an mRNA molecule and moves along it, capturing loaded tRNA molecules and joining together their amino acids to form a new protein chain.[3]
Protein production The oldest and most widely used expression systems are cell-based and may be defined as the "combination of an expression vector, its cloned DNA, and the host for the vector that provide a context to allow foreign gene function in a host cell, that is, produce proteins at a high level".[9][10] Overexpression is an abnormally and excessively high level of gene expression which produces a pronounced gene-related phenotype.[11][12]