Chemistry
messenger RNA
Messenger RNA (mRNA) is a type of RNA molecule that carries genetic information from the DNA in the cell nucleus to the ribosomes in the cytoplasm. It serves as a template for protein synthesis, carrying the instructions for the sequence of amino acids in a protein. mRNA plays a crucial role in the process of gene expression and protein production within cells.
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3 Key excerpts on "messenger RNA"
eBook - PDF- S Bresler(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Chapter V RNA Function 1. Introduction Ribonucleic acid (RNA) is the second component of living tissue which performs a cybernetic function, in this case by providing and supporting a flow of information in the cell. Its role is perhaps even more complicated than that of deoxyribonucleic acid (DNA). While DNA stores the information necessary for the growth and repro-duction of each cell, different types of RNA participate directly in this process, supplying working components of the protein-synthesizing machinery. Accordingly, the quantity of DNA in the cell is invariant, and even in complex and highly differ-entiated organisms, all cells contain the same amount of this substance. By contrast, the quantity of RNA per cell varies substantially, depending on the rate of protein synthesis. The latter is influenced in its turn by external conditions of growth such as the carbon source, temperature, and nutrient supplements. The synthesis of each specific enzyme or protein is determined by a special kind of RNA which contains the necessary information in the form of a chemical code akin to that of DNA. But in addition to carrying information about protein structure, RNA also plays a role in controlling the rate of synthesis of each protein. The mechanism by which protein synthesis is regulated depends in large measure on interactions bet-ween the cell and its surrounding medium. In this chapter we shall consider the feedback loop which permits the cell to initiate the synthesis of just the enzyme or enzymes it needs to cope with a particular change in the environment. We should emphasize at this point that the number of informational RNA molecules of a given type present in the cell at any one time is a material reflection of the operation of this mechanism. The result will be the rapid synthesis of one or more enzymes for which there is a 449 450 V. RNA Function need and the inhibition or decline in the synthesis of others not as essential for efficient growth.
eBook - PDF- Belal E. Baaquie, Frederick H. Willeboordse(Authors)
- 2009(Publication Date)
- CRC Press(Publisher)
Finally, this pre-miRNA is then processed into miRNA in the cytoplasm. Thus, once again, we find that RNA does an excellent job in yet another cate-gory of function. 16.6 RNA genes In modern cells, information is stored in DNA. Those parts of the DNA that encode the information for the production of proteins are called genes. However, besides proteins, as we have seen in the sections above, there are many essential RNA molecules. Not surprisingly, the information for these molecules is also stored in the DNA in regions that are called RNA genes. The resulting RNA molecules, for example, the catalyst rRNA or the transport molecule tRNA, are then called non-coding RNA (ncRNA) since they do not code for proteins. 16.7 Overview The main RNA functions with regard to protein production are summarized in Table 16.1. Molecule Abbreviation Function transfer RNA tRNA brings amino acid monomers to ribosome messenger RNA mRNA brings instruction for protein to ribosome ribosomal RNA rRNA catalyzes the joining of amino acids Table 16.1: Key RNA types for protein manufacture. tRNA and rRNA are non-coding while mRNA is coding. Some of the other noncoding RNA not involved in protein synthesis are listed in Table 16.2. Given names such as small and micro, one might be tempted to assume that that all noncoding RNA is relatively small. This is not the case, however. For 352 Exploring Integrated Science Molecule Abbreviation Function small nuclear RNA snRNA regulatory functions in eukaryotic nuclei efference RNA eRNA gene regulation transfer-messenger RNA tmRNA identifies faulty ribosomal activity in bacteria small interfering RNA siRNA regulates gene expression and com-bats viruses micro RNA miRNA control gene expression Table 16.2: Key noncoding RNA types. example, in female mammals, one of the two X chromosomes is inactivated (so as to have the same number of active X chromosomes as males — namely, one) by an RNA gene named Xist that is 18,000 base pairs long.
eBook - PDF- Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Not all noncoding transcripts are small. A number of evolutionarily conserved, long (>200 bases) ncRNAs (e.g., XIST, HOTAIR, and AIRE) that function as regulators of chromatin structure or gene transcription have also been discovered, as discussed in Sections 12.3 and 12.7, respectively. Genomic studies show that there are thousands of conserved long ncRNAs (lncRNAs), and the few for which biological functions have been identified are only the tip of the iceberg. It is even possible that the vast transcriptional output of the mammalian genome holds the key to explain- ing why we have approximately the same number of genes as organisms we believe to be much less complex (see Fig- ure 10.28). Regardless of the actual explanation, one point is clear: There is a great deal that we do not understand about the many roles of RNAs in eukaryotic cells. Review 1. Compare and contrast CRISPR RNA with piRNA, in terms of how the RNAs are produced and what pro- teins are associated with them. 2. Why is the ability of the CRISPR system to cut DNA so useful for researchers? Why is it impossible to use RNAi for the same purpose? 11.8 Encoding Genetic Information Once the structure of DNA had been revealed in 1953, it became evident that the sequence of amino acids in a polypeptide was specified by the sequence of nucleotides in the DNA of a gene. It seemed very unlikely that DNA could serve as a direct, phys- ical template for the assembly of a protein. Instead, it was pre- sumed that the information stored in the nucleotide sequence was present in some type of genetic code. With the discovery of messenger RNA as an intermediate in the flow of information from DNA to protein, attention turned to the manner in which a sequence written in a ribonucleotide “alphabet” might code for a sequence in an “alphabet” consisting of amino acids.
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