Structure, Replication, and Transcription of DNA for AP Biology (page 2)

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By — McGraw-Hill Professional
Updated on Oct 24, 2011

Transcription of DNA

Up until this point, we have just been discussing DNA replication, which is simply the production of more DNA. In the rest of the chapter, we discuss transcription, translation, and other processes involving DNA. While DNA is the hereditary material responsible for the passage of traits from generation to generation, DNA does not directly produce the proteins that it encodes. DNA must first be transcribed into an intermediary: mRNA. This process is called transcription (Figure 11.5) because both DNA and RNA are built from nucleotides—they speak a similar language. DNA acts as a template for mRNA, which then conveys to the ribosomes the blueprints for producing the protein of interest. Transcription occurs in the nucleus.

Transcription of DNA

Transcription consists of three steps: initiation, elongation, and termination. The process begins when RNA polymerase attaches to the promoter region of a DNA strand (initiation). A promoter region is simply a recognition site that shows the polymerase where transcription should begin. The promoter region contains a group of nucleotides known as the TATA box, which is important to the binding of RNA polymerase. As in DNA replication, the polymerase of transcription needs the assistance of helper proteins to find and attach to the promoter region. These helpers are called transcription factors. Once bound, the RNA polymerase works its magic by adding the appropriate RNA nucleotide to the 3' end of the growing strand (elongation). Like DNA polymerase of replication, RNA polymerase adds nucleotides 5' to 3'. The growing mRNA strand separates from the DNA as it grows longer. A region called the termination site tells the polymerase when transcription should conclude (termination). After reaching this site, the mRNA is released and set free.


Practice problems for these concepts can be found at: Molecular Genetics Review Questions for AP Biology

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