Protein Production

2 Key excerpts on "Protein Production"

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  eBook - ePub

  Advanced Molecular Biology

  A Concise Reference

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

    (Publisher)

  Chapter 23

  Protein Synthesis

  Fundamental concepts and definitions

  • Protein synthesis is the level of gene expression where genetic information carried as a messenger RNA (mRNA) molecule is translated into a polypeptide.
  • The components of the protein synthesis machinery are mRNA, the template which contains the code to be translated, ribosomes, large ribonucleoprotein particles which are the sites of protein synthesis, transfer RNA (tRNA), versatile adaptor molecules which carry amino acids to the ribosome and facilitate the process of translation, and accessory factors associating transiently with the ribosome, required for ribosome assembly and disassembly, and its activity during elongation.
  • Like other polymerization reactions, protein synthesis has stages of initiation, elongation and termination, each of which may be regulated. The protein synthesis mechanism is similar in prokaryotes and eukaryotes, but there are subtle differences in the nature of the components and their order of assembly. There are major differences, however, concerning the context in which protein synthesis occurs. In bacteria, transcription and protein synthesis occur simultaneously in the cytoplasm (allowing cross-regulation between different levels of gene expression) and mRNA may be polycistronic. In eukaryotes, transcription is confined to the nucleus and the mRNA is exported to the cytoplasm for translation. Nascent mRNA is extensively processed before export and is usually monocistronic (see RNA Processing).
  • Following synthesis, a polypeptide undergoes further processing before becoming active. 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

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  eBook - ePub

  Molecular Biology

  • David P. Clark(Author)
  • 2009(Publication Date)
  • Academic Cell

    (Publisher)

  3 for a brief overview). The genetic information is transmitted in two stages. First the information in the DNA is transcribed into messenger RNA (mRNA). The next step uses the information carried by the mRNA to give the sequence of amino acids making up a polypeptide chain. This involves converting the nucleic acid “language,” the genetic code, to protein “language,” and is therefore known as translation. This overall flow of information in biological cells from DNA to RNA to protein is known as the central dogma of molecular biology (see Chapter 3, Fig. 3.17) and was first formulated by Sir Francis Crick. Ribosomes use the information carried by messenger RNA to make proteins. The decoding of mRNA is carried out by a submicroscopic machine called a ribosome, which binds the mRNA and translates it. The ribosome moves along the mRNA reading the message and synthesizing a new polypeptide chain. Bacterial protein synthesis will be discussed first. The process is similar in higher organisms, but some of the details differ and will be considered later. Proteins Are Gene Products An early rule of molecular biology was Beadle and Tatum’s dictum: “one gene—one enzyme” (see Ch. 1). This rule was later broadened to include other proteins in addition to enzymes. Proteins are therefore often referred to as “gene products.” However, it must be remembered that some RNA molecules (such as tRNA, rRNA, small nuclear RNA) are never translated into protein and are therefore also gene products. Gene products include proteins as well as non-coding RNA Furthermore, instances are now known where one gene may encode multiple proteins (Fig. 8.01). Two relatively widespread cases of this are known—alternative splicing and polyproteins. In eukaryotic cells, the coding sequences of genes are often interrupted by non-coding regions, the introns. These introns are removed by splicing at the level of messenger RNA

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