BIOLTranscription - DNA, Genes, and Proteins From DNA to...

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DNA, Genes, and Proteins From DNA to Protein Specific proteins perform a variety of important functions in the body. They may act as catalysts to control reactions, act as antibodies in the immune system, transport materials around the body, form the physical structures that allow organisms to move, or control the movement of substances into and out of cells. The instructions for making specific proteins are controlled by genes housed in DNA. Since genes control the production of proteins, they have enormous influence on the physical characteristics of an organism. Francis Crick, one of the discoverers of the structure of DNA, is also known for formulating the central dogma of molecular biology. This dogma states that information flows from DNA to RNA to protein, but not from the protein back to RNA or DNA. The pathway of protein information runs one way: DNA → RNA → protein Protein production occurs in two phases: 1. Transcription: During transcription, information in DNA is transcribed, or rewritten, onto a strand of messenger RNA (mRNA). 2. Translation: During translation, the information written onto the mRNA is used to assemble a protein. Transcription Transcription, the process by which information from DNA is transferred to mRNA, occurs in the nucleus of the cell. DNA is unwound at a specific gene, and mRNA is formed via complementary base pairing at one strand of the DNA. Transcription can be described in three steps: 1. Initiation: The enzyme RNA polymerase binds to the promoter region of DNA at the start of a gene. RNA polymerase unwinds the DNA and starts to assemble the mRNA. 2. Elongation: The RNA polymerase moves down the DNA strand, assembling the mRNA from 5' to 3'. Through complementary base pairings, the mRNA assembles along one strand of DNA, known as the template strand. 3. Termination: The RNA polymerase reaches a stop signal, a certain series of bases within the DNA. Transcription ceases, and the mRNA dissociates from the template strand of DNA. EXAMPLE: As a result of complementary base pairings, the template strand 3' TACTTGGCGATT 5' would be transcribed into the following mRNA: 5'AUGAACCGCUAA 3'.
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Transcription mRNA Modification After transcription, the mRNA of eukaryotic cells undergoes two modifications to protect it as the mRNA moves from the nucleus to the cytoplasm. (Since transcription occurs in the cytoplasm for prokaryotic cells, these modifications do not occur in prokaryotic cells.) Extra bases are added at the beginning and end of the mRNA strand, forming a cap and tail. The cap and tail protect the mRNA from degradation caused by enzymes as the mRNA travels from the nucleus to the cytoplasm for translation. Introns, noncoding regions of the mRNA strand, are removed in a process called RNA splicing. The coding regions of mRNA, called exons, are attached together. Posttranscriptional RNA Processing
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This note was uploaded on 03/06/2011 for the course BIOL 100B taught by Professor Nargesshassanzadeh-kiabi during the Winter '08 term at California State University Los Angeles .

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BIOLTranscription - DNA, Genes, and Proteins From DNA to...

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