RNA messenger

Messenger RNA molecules in prokaryotic and eukaryotic cells are similar in some structural aspects but also differ significantly. All messenger RNAs contain the same four nucleotides. A, C, G, and U, and utilize the codon AUG to 

The introns (intervening sequences) are spliced out of the primary transcript and the exons (expressed 

While transcription is in process, the 5 end of the mRNA is capped with a methyl guanine nucleotide (m Gppp). 

After the primary transcript is complete, a polyA tail (-AAA Aoh) is added to the 3 terminus. 

Structures of prokaryotic and eukaryotic primary transcripts (mRNAs). Prokaryotic mRNAs are polygenic, do not contain introns or exons, and are short lived in the cell. Eukaryotic mRNAs are monogenic, contain introns and exons, and usually are long lived in the cell. 

The functional roles of rRNAs include the participation in mRNA selection, tRNA binding, ribosomal subunit association, frame-shift snppression, translational proofreading, binding of various factors and peptidyl transferase activity. Messenger RNA is selected by interaction with the 3 -terminus of 16S rRNA in the platform region of the small subunit. tRNA interacts with 16S rRNA in the cleft of the small subunit and around the universally conserved central loop of 23 S rRNA (via CCA terminal of tRNA) of the large subunit. This conserved region of rRNA may be involved in the peptidyl transferase activity. Subunit interaction appears to involve elements of both 16S and 23S rRNA. 

Messenger RNA (mRNA) is transcribed from DNA containing the information to encode protein synthesis and characterized by the following properties  

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In RNA the sugar is ribose and uracil replaces thymine. Different varieties of RNA exist with widely different molecular weights. Messenger RNA conveys information in the form of the sequence of bases from DNA to RNA on the ribosomes, where proteins are... 

Section 28 11 Three RNAs are involved m gene expression In the transcription phase a strand of messenger RNA (mRNA) is synthesized from a DNA tern plate The four bases A G C and U taken three at a time generate 64 possible combinations called codons These 64 codons comprise the genetic code and code for the 20 ammo acids found m proteins plus start and stop signals The mRNA sequence is translated into a prescribed protein sequence at the ribosomes There small polynucleotides called... 

Messenger RNA (mRNA) (Section 28 11) A polynucleotide of nbosethat reads the sequence of bases in DNA and inter acts with tRNAs in the nbosomes to promote protein biosynthesis... 

For example, a polypeptide is synthesized as a linear polymer derived from the 20 natural amino acids by translation of a nucleotide sequence present in a messenger RNA (mRNA). The mature protein exists as a weU-defined three-dimensional stmcture. The information necessary to specify the final (tertiary) stmcture of the protein is present in the molecule itself, in the form of the specific sequence of amino acids that form the protein (57). This information is used in the form of myriad noncovalent interactions (such as those in Table 1) that first form relatively simple local stmctural motifs (helix... 

If an antibody to the protein of interest is available, it is sometimes possible to use vector sequences, eg, the beta-galactosidase promoter sequence, to direct the transcription of the passenger DNA into messenger RNA and the translation of that mRNA into protein which can be recognized by the antibody. Although this method is somewhat less reHable than the use of nucleic acid probes, specialized vectors are available for this purpose. 

Ara-A is phosphorylated in mammalian cells to ara-AMP by adenosine kinase and deoxycytidine kinase. Further phosphorylation to the di- and triphosphates, ara-ADP and ara-ATP, also occurs. In HSV-1 infected cells, ara-A also is converted to ara-ATP. Levels of ara-ATP correlate directly with HSV rephcation. It has recently been suggested that ara-A also may exhibit an antiviral effect against adenovims by inhibiting polyadenylation of viral messenger RNA (mRNA), which may then inhibit the proper transport of the viral mRNA from the cell nucleus. 

In contrast, RNA occurs in multiple copies and various forms (Table 11.2). Cells contain up to eight times as much RNA as DNA. RNA has a number of important biological functions, and on this basis, RNA molecules are categorized into several major types messenger RNA, ribosomal RNA, and transfer RNA. Eukaryotic cells contain an additional type, small nuclear RNA (snRNA). With these basic definitions in mind, let s now briefly consider the chemical and structural nature of DNA and the various RNAs. Chapter 12 elaborates on methods to determine the primary structure of nucleic acids by sequencing methods and discusses the secondary and tertiary structures of DNA and RNA. Part rV, Information Transfer, includes a detailed treatment of the dynamic role of nucleic acids in the molecular biology of the cell. 

Messenger RNA (mRNA) serves to carry the information or message that is encoded in genes to the sites of protein synthesis in the cell, where this information is translated into a polypeptide sequence. Because mRNA molecules are transcribed copies of the protein-coding genetic units that comprise most of DNA, mRNA is said to be the DNA-like RNA. ... 

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