Messenger RNA molecule

Figure 35-10. The cap structure attached to the 5 terminal of most eukaryotic messenger RNA molecules. A 7-methylguanosine triphosphate (black) is attached at the 5 terminal of the mRNA (shown in blue), which usually contains a 2 -0-methylpurine nucleotide.

Fig. 24.4 Splicing of a messenger RNA molecule transcribed from a hypothetical insulin gene containing two introns.

Messenger RNA molecules for both subunits of the cytochrome and the two cytosolic components are detectable in unstimulated bloodstream cells. Experiments involving incubation of neutrophil suspensions with the protein synthesis inhibitor cycloheximide indicate that constitutive expression of one or more components of the oxidase is required for the neutrophil to maintain its ability to generate reactive oxidants. For example, when neutrophils are incubated in vitro with cycloheximide, their ability to generate reactive oxidants declines more rapidly than in control cells, as they age in culture (Fig. 7.12). This decline in oxidase activity when protein biosynthesis is blocked is not due to cell death, because cells treated with cycloheximide for this time still exclude trypan blue. Furthermore, when protein biosynthesis is stimulated in neutrophils by the addition of GM-CSF for 24 h in vitro, the ability to generate reactive oxidants is enhanced considerably above the levels observed in untreated cells. 

The various ways in which messenger RNA molecules may be spliced provides a mechanism for diversity in protein structures derived from a single gene. 

Nearly all of the RNA of the cell is synthesized (transcribed) in the nucleus, according to the instructions encoded in the DNA. Some of the RNA then moves out of the nucleus into the cytoplasm where it functions in protein synthesis and in some other ways. Many eukaryotic genes consist of several sequences that may be separated in the DNA of a chromosome by intervening sequences of hundreds or thousands of base pairs. The long RNA transcripts made from these split genes must be cut and spliced in the nucleus to form the correct messenger RNA molecules which are then sent out to the ribosomes in the cytoplasm. 

Transfer of information from DNA to protein. The nucleotide sequence in DNA specifies the sequence of amino acids in a polypeptide. DNA usually exists as a two-chain helical structure. The information contained in the nucleotide sequence of only one of the DNA chains is used to specify the nucleotide sequence of the messenger RNA molecule (mRNA). This sequence information is used in polypeptide synthesis. A three-nucleotide sequence in the mRNA molecule codes for a specific amino acid in the polypeptide chain. (Illustration copyright by Irving Geis. Reprinted by permission.)... 

The arrangement of amino acids in polypeptide chains is determined by the arrangement of codons in messenger RNA molecules. 

Codon. In a messenger RNA molecule, a sequence of three bases that represents a particular amino acid. 

The genetic information in a gene is copied (transcribed) into a messenger RNA molecule (mRNA), preserving the sequence by complementary base-pairing. The introns are cut and the mRNA molecule is transported into the cytoplasm where it directs the synthesis of protein at the ribosomes. The sequence of bases is translated into a sequence of amino acid residues by a triplet code wherein three bases specify one amino acid. 

Specific inhibition of templated biosynthesis by electroneutral polynucleotide analogs can be achieved even with complex templates Messenger RNA coding for globin, similarly to other messenger RNA molecules, contains a polyadenylate sequence located... 

Messenger RNA combines with ribosomes to form polysomes containing several ribosome units, usually 5 (e.g., during hemoglobin synthesis), complexed to the messenger RNA molecule. This aggregate structure is the active template for protein biosynthesis. 

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