Transcription is the synthesis of RNA under the direction of DNA. The DNA strand is used as a template during RNA synthesis. Both DNA and RNA use the same language, genetic code, and the language is simply transcribed, or copied, from one molecule to another. Genetic code is series of nucleotide base pairs, that code for heritary information and information involving the synthesis of molecules and of the organism in general. A strand of DNA is unwound by RNA Polymerase. The single strand of DNA acts as a template strand from which a copy can be made. The other strand of DNA left is the coding strand. The RNA that results from the copying of the DNA nucleotides is messenger RNA. After RNA synthesis, translation occurs. Translation is the actual synthesis of a polypeptide, and it occurs under the direction of mRNA. A polypeptide chain is a long string of amino acids linked together before the final protein has been completed. Amino acids are organic molecules used to make proteins. A Messenger RNA codes for each amino acid that is added onto the polypeptide chain. In the genetic code, nucleotide triplets specify amino acids. RNA Polymerase is an enzyme that pries apart two strands of DNA and hooks together the RNA nucleotides as
they base-pair along the DNA template. The RNA Polymerase works in the direction of 5’ to 3’. RNA Polymerase can add nucleotides only to the 3’ end. Specific sequences of DNA mark where transcription of a gene begins and ends. The DNA sequence from where RNA polymerase attaches and initiates transcription is known as the promoter; the sequence that signals the end of transcription is called the terminator. The stretch of nucleotides between the two, is called a transcription unit. In eukaryotes, a collection of proteins called transcription factors regulate the binding of RNA polymerase. Certain transcription factors must bind with the promoter and RNA polymerase before initiation can begin. Eukaryotic promoters often include a TATA box, a nucleotide sequence containing TATA, about 25 nucleotides upstream from the starting point. A transcription factor that recognizes the TAT box must bind to the DNA before RNA polymerase II can do so. Am enzyme adds on a string of adenines to the end of an mRNA molecule. This is called a poly(A) tail. The front of the molecule is give a 5’ cap, made of a modified guanine nucleotide. The cap helps to stop degradation , and later it acts as an “attach here” sign for ribosomes
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