Transcription always proceeds from one of the two DNA strands, which is called the template strand. Enzymes and other proteins involved in transcription bind at the promoter. ![]() The initiation of transcription begins when DNA is unwound, forming a transcription bubble. The specific sequence of a promoter is very important because it determines whether the corresponding gene is transcribed all of the time, some of the time, or hardly at all ( Figure 2).įigure 2. In most cases, promoters exist upstream of the genes they regulate. The DNA sequence onto which the proteins and enzymes involved in transcription bind to initiate the process is called a promoter. The region of unwinding is called a transcription bubble. Transcription requires the DNA double helix to partially unwind in the region of mRNA synthesis. Because genes in animal cells are found in the nucleus, transcription occurs in the nucleus of the cell and the mRNA transcript must be transported to the cytoplasm. Transcription occurs in three main stages: initiation, elongation and termination. However, as we shall see in the next module, the translation to protein is still systematic, such that nucleotides 1 to 3 correspond to amino acid 1, nucleotides 4 to 6 correspond to amino acid 2, and so on. The translation to protein is more complex because groups of three mRNA nucleotides correspond to one amino acid of the protein sequence. The copying of DNA to mRNA is relatively straightforward, with one nucleotide being added to the mRNA strand for every complementary nucleotide read in the DNA strand. The central dogma states that DNA encodes RNA, which in turn encodes protein. The flow of genetic information in cells from DNA to mRNA to protein is described by the central dogma ( Figure 1), which states that genes specify the sequences of mRNAs, which in turn specify the sequences of proteins.įigure 1. * The Central Dogma: DNA Encodes RNA RNA Encodes Protein ![]() This module discusses the details of transcription. Through the processes of transcription and translation, a protein is built with a specific sequence of amino acids that was originally encoded in the DNA. ![]() The mRNA then provides the code to form a protein by a process called translation. To do this, the DNA is “read” or transcribed into an mRNA molecule. In all cells, the second function of DNA (the first was replication) is to provide the information needed to construct the proteins necessary so that the cell can perform all of its functions. Theme 2: How Does Blood and Organ Donation Work?
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