Principles of Biochemistry (2): Transcription

*Disclaimer: In this series, we will introduce Dr. Michael Behe, from his book Supplement (Darwin's Black Box: The Biochemistry Challenge of Evolution) Transcribation DNA is the repository of information, a polynucleotide, and tells the information carried by the cell how to make polypeptides, but how to translate the information from one polymeric language to another? Not long after the discovery of the double helix structure of DNA, physicist George Gamow proposed the non-chemical idea that information is abbreviated in symbols, and that the expression of that information is made after decoding the nucleotide and translating the message into polypeptides, which are written in the language of proteins. During the 1960s, the code was broken when Nobel laureates Marshall Nirenberg, Severo Ochoa, and their collaborators demonstrated that three consecutive nucleotides encode one amino acid (Figure A-4). Since there are 64 possible combinations, so we have four different base types that are repeated three times, this means that there is more compatibility than we need to encode 20 base amino acids. Most acids have two or more codons, but there are several that are coded by a single codon, but in the end the total probability of coding amino acids is 61 out of 64, where three codons are allocated to be used as a stop signal, and once these signals enter the protease synthesizer the process of protein production stops at that point. The large number of steps involved in extracting information from DNA can be divided into two basic stages called transcription and translation, in short, the cell in the transcription stage makes a copy of the DNA piece that we call the gene and that symbolizes proteins, while in translation the information in RNA is used to produce the protein. Gene transcription entails many decisions. The first is where to start from the long DNA sequence. The starting position is often marked by several special DNA sequences called promotors. In prokaryotes there is a sequence of nucleotides, usually TCTTGACAT, called Zone-35 and comes 35 nucleotides ahead of The gene, another sequence that is usually TATAAT and is called a Pribnow box, comes 5 to 10 bases ahead of the transcription initiation site. Eukaryotic nuclei have similar signals, sequences of DNA called enhancer, which is thousands of base pairs away from where the transcription begins, and has an important influence on the rate at which the gene is cloned. In order for transcription to begin in prokaryotics, many of the enzymatic "units" that make up an enzyme called RNA polymerase must bind to DNA. RNA polymerase consists of 5 polypeptide chains. Initially, the enzyme is weakly bound, moving along the DNA like a train on a rail, until it finds the prokaryotic region of the gene, where one of the protein monomers, called sigma, recognizes the DNA sequence. In the absence of , RNA polymerase is tightly bound to DNA, and can no longer move freely, and now it starts to work, as the pairs are separated along about 10 bases of DNA, so the two energies are separated from each other in that area, and this is necessary for the RNA chain that will be formed to read the DNA template by forming hydrogen bonds with it. Now the activated ribonucleotide polymerase that corresponds to the first base in DNA, begins the process. Once the first ribonucleotidine is integrated with the mold, the RNA polymerase chemically binds them, then moves forward along the dendritic mold, spacing the DNA energy as it proceeds. The ribonucleotide, which completes the third position and chemically binds it, enlarges the chain, repeating these steps along the gene at a very high rate, moving at about 20-50 nucleotide pairs per second. Cloning causes a problem, which is that the movement of the polymerase forward through the coiled inferior helix causes a larger and tighter wrap. (4) This may cause the transcription process to slow down or stop completely unless another protein (topoisomerase) dissolves the DNA wrap with a complex maneuver, cutting off the uncut DNA energy through the cut energy and then re-bonding the pieces. The transcription process stops when RNA polymerase passes a certain sequence of DNA. This sequence in prokaryotes is a symmetrical region5 for its middle, and contains about 6 or 7 pairs of GC bases, followed by a similar region rich in AT pairs. Some (but not all) genes require an extra protein to separate the DNA from the protein. — Source: Published on Facebook's "Braheen Center" page https://www.facebook.com/braheen.org/posts/pfbid0GYorKpRGWmyACY3mzHha6PuX1eJAfFh43m53a6BTXWyubWZufBfqApQRi793BMhLl