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GeneExpressionPrint - Gene Expression While we wear certain...

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While we wear certain styles of blue jeans to express our individuality, gene expression regulate our unique genetic makeup. Gene Expression
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Gene expression is an umbrella term that describes how the information encoded by a gene is turned into a phenotype, most often the creation of a protein. The gene is the starting point of protein synthesis. The order of the DNA nucleotides in a gene (or a gene's sequence ) directs which amino acids will be included and the order they will be assembled in the final protein. The information contained within the DNA sequence of a gene is first transcribed into mRNA and then translated into protein. Gene expression can be regulated by controlling the spatial (where) and temporal (when) transcription of genes. At the end of this e-module, you should be familiar with the details of transcription and translation . What is a gene? The term gene describes all the DNA sequence required to make a protein and includes: the promoter, a start codon, an open reading frame, and a stop codon (see figure 1). The promoter is the region of DNA that the RNA polymerase recognizes and binds to prior to starting transcription. The open reading frame is the DNA sequence that encodes the protein. The start and stop codons are the boundaries of the protein coding sequence. The purpose of all these elements will become clearer as we learn more about transcription and translation. Gene Expression
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Transcription (DNA to RNA) Transcription is a reaction in which the information contained within a DNA sequence is transferred to RNA. We often think of transcription as generating only mRNAs from the protein coding information contained within genes, but transcription also generates other types of RNA. The physical process of transcription is similar to replication, but this time a RNA polymerase makes an RNA copy of a DNA sequence instead of a DNA polymerase making a DNA copy. Another difference between replication and transcription is that only one strand of the double-stranded DNA, the template strand, is transcribed into RNA. The non-template strand is called the coding strand. RNA polymerase is the enzyme that links together RNA nucleotides to form RNA. RNA polymerase recognizes and binds to the promoter of a gene and begins to transcribe the DNA sequence into RNA. Just like DNA polymerase, RNA polymerase links the 5' phosphate group of a new nucleotide to the 3'OH of the nucleotide at the end of the growing chain. RNA polymerase functions to both separate the two strands of DNA and copy the template strand into a RNA transcript (see figure 2). When the RNA polymerase reaches the end of the coding sequence and recognizes a termination site, the RNA polymerase stops adding RNA nucleotides and the mRNA is released. From there, the mRNA is exported out of the nucleus and into the cytoplasm via nuclear pores found on the surface of the nucleus. The new mRNA is an exact copy of the “coding” strand of DNA, except that all the thymine nucleotides have been replaced with uracil nucleotides (see figure 3).
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