messenger RNA

2 Key excerpts on "messenger RNA"

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  eBook - ePub

  Plant Genes, Genomes and Genetics

  • Erich Grotewold, Joseph Chappell, Elizabeth A. Kellogg(Authors)
  • 2015(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Yet, as will be described below, it is now clear that information can also flow from RNA to DNA, and thus the Central Dogma is not as unidirectional as originally thought. RNA plays a central role in this flow of information. However, we will also see that RNA has a number of other fundamental cellular functions, including structural and catalytic roles. A typical eukaryotic cell, such as a plant cell, carries many distinct types of RNA molecules, which can be differentiated by some unique characteristics (Figure 6.2 and Table 6.1). messenger RNA (mRNA), corresponding to just 2–4% of the total RNA in the cell, conveys the bulk of the genetic information from the DNA to the proteins. mRNAs can range in size from a few hundred to several thousand nucleotides. They typically carry a cap at the 5′ end, consisting of modified guanine nucleotide and a 3′ tail formed by up to several hundred adenosine nucleotides (polyA tail). RNA modifications are discussed at the beginning of Part 3 of this book, and mRNAs are a main focus of Chapter 8. Figure 6.1 The Central Dogma of Biology. Arrows indicate the flow of information Figure 6.2 Diagrams showing main characteristics of various RNAs (tRNA, rRNA and mRNA). The different colors in the tRNA illustrate the various arms and loops. For example, the orange corresponds to the D arm and loop, the red corresponds to the anticodon arm and loop, the green corresponds to the T arm and loop, and the blue corresponds to the amino acid acceptor arm (the amino acid gets covalently linked to the 3′ end, which harbors the –OH group)

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  eBook - ePub

  Advanced Molecular Biology

  A Concise Reference

  • Richard Twyman(Author)
  • 2018(Publication Date)
  • Garland Science

    (Publisher)

  It must fold correctly, a process sometimes requiring the assistance of a molecular chaperone (q.v.). It may be cleaved, and specific residues may be chemically modified or conjugated to small molecules. Such modifications are often associated with the targeting of proteins to specific compartments in the cell or for secretion. Proteins may need to associate noncovalently with other proteins or with nonpolypeptide cofactors for their full activity. For a discussion of these processes, see Proteins: Structure, function and evolution. 23.1 The components of protein synthesis messenger RNA. messenger RNA (mRNA) is the template for protein synthesis. It has two essential features: an open reading frame (a sequence of translatable codons) and a ribosome binding site (where the small ribosome subunit binds and the rest of the ribosome assembles). There are important distinctions between prokaryotes and eukaryotes with respect to the organization of these sites, and also concerning other aspects of the life of a typical mRNA molecule. These differences and their consequences are summarized below. (1) In bacteria, transcription and translation occur simultaneously in the same cellular compartment, whereas in eukaryotes, transcription is restricted to the nucleus and RNA must be exported into the cytoplasm for translation. (2) Bacterial mRNA has a limited half-life (several minutes for the most stable transcripts). Some eukaryote mRNAs are also unstable, but most are stable for hours or even days (e.g. in eggs). (3) Bacterial transcripts are used directly for translation, whereas eukaryotic transcripts are extensively processed and modified beforehand. Processing reactions include the splicing of introns and 3′ end polyadenylation; both may regulate the efficiency of translation, either directly or by modulating mRNA stability. A further modification is the synthesis of a 5′ end 7-methylguanosine cap, which has a direct role in ribosome binding

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