Gene transcription/translation is the process by which a cell creates a protein. An enzyme, RNA polymerase II, physically moves along the DNA strand on the chromatin where the gene is located and reads the nucleotide sequence to create a complementary RNA molecule. The RNA molecule is modified inside the nucleus before it exports into the cytosol. An extension of As are added to the 3' end, and modified Gs are added to the 5' end of the RNA molecule. The extensions allow the RNA molecule to exit nucleus, they prevent degradation by exonucleases of the RNA that codes for the protein, and they help the RNA find and bind to a ribosome. In the cytoplasm, the mRNA molecule is translateted by tRNA molecules with the help of a ribosome. Specific tRNAs with a specific amino acid attached to each one bind to their specific set of three nucleotide bases (a codon) on the RNA molecule within the ribosome. As the ribosome moves along the RNA molecule, different tRNAs enter the ribosome and leave their corresponding amino acid when bound to their designated codon. The amino acids form peptide bonds with one another as the amino acid sequence grows, and a protein is formed. The protein is then modified to further determine its function. The addition of biochemical functional groups, or the cleavage of polypeptides upon activation of the protein are common post-translational modifications. This song is about transcription.
A promoter is a region of DNA that facilitates or regulates the transcription process for a specific gene, located near that gene, and ultimately regulates the production of the protein encoded by that gene. For example, the TATA box promoter is the region of DNA that exists before every gene and facilitates transcription by recruiting proteins that initiate the transcription process for that gene it proceeds. It is called the TATA box promoter because regardless of how long and complex the promoter is, determined by the amount of regulation that the gene requires, this region of DNA always contains the nucleotide sequence TATA and serves as the initiation site for gene transcription. This is where proteins will bind and recruit RNA polymerase II to begin transcription of the gene encoded by the DNA strand.
General transcription factors are the proteins that bind to the TATA box promoter and initiate the transcription of all of our genes by recruiting and stabilizing the RNA polymerase II enzyme while it transcribes the gene. The TATA binding protein (TBP) binds to the TATA box promoter and recruits the general transcription factors that recruit/stabilize RNA polymerase II.
The enzyme, RNA pol. II has the ability to "un-zip" the double-stranded DNA, or temporarily break the hydrogen bonds of complementary nucleotide bases, to temporarily separate the strand of DNA to be coppied. RNA polymerase II transcribes the DNA strand and creates a single-stranded RNA molecule with a complementary nuleotide sequence to that of the DNA strand.
For RNA polymerase II enzymes to transcribe a gene at their maximum rates producing RNA molecules as fast as possible, the gene must be made more accessable to the enzymes. Isolated human DNA from any one cell stretches about 3 meters long. For our DNA to fit inside the nuclei of our cells, the DNA is tightly wound and packed around proteins called histones to form chromatin. Distal promoters, or enhancers (regulatory units of DNA far from the gene it regulates), recruit activator proteins which recruit co-activator enzymes which loosen the DNA from the histones with their histone acetyl transferase activity. These co-activator enzymes disrupt the +/- attraction of the DNA to the histone by transfering an actyl group to the positive lysine tails on the histones. The DNA (negatively charged) is no longer attracted to the histone and falls off for RNA polymerase II to maximally transcribe.
Expansions of nucleotide sequences in the DNA that do not code for a protein and are found throughout a gene (introns) are transcribed by RNA pol. II and then spliced, or removed, from the final mRNA molecule . The regions of the RNA that do code for a protein (exons) are ligated together. Splicosomes are the proteins that are responsible for removing the introns and ligating the exons of the RNA molecule. The regions of DNA that do not encode a protein, and are found throughout a gene, minimize the probability that a mutation will affect the region of DNA that does codes for the protein.
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Transcription Complex,Enhancers & silencersby HaroonBBT6,093 views
Hey this was fucking helpful!
wearashirt 6 months ago 2
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Reeznarch 10 months ago 4