Translation in protein synthesis

With some RNA vimses, e.g. poliovims, the RNA strand fi cm the particle can act directly as mRNA and is translated into viral proteins on the host-cell ribosomes. In many other RNA vimses, however (e.g. the influenza vimses), the RNA strands are negative-sense RNAs (anhmessages) that have first to be transcribed to the complementary sequence by RNA-dependent RNA polymerases before they can function in protein synthesis. Sinee eukaryotie eells do not have these enzymes, the negative-sense RNA vimses must earry them in the virion. 

This definition expands our earlier thoughts in two ways. First, we have included specification of RNA molecules as well as proteins. As noted above, many RNA molecules serve a role as message carrier from DNA to the protein-synthesizing machinery (mRNA) and are translated into protein structures. Other RNA molecules serve other functions as components of the ribosome, rRNA, or as an interface between mRNA and amino acids in protein synthesis, tRNA. Finally, we have the very small RNA molecules known as siRNA. These species of RNA are not translated into proteins and this requires that the definition of a gene include the specification of their structure. 

There are at least two answers to question (i). First, abnormal proteins can arise in cells due to spontaneous denaturation, errors in protein synthesis, errors in post-translational processing, failure of the correct folding of the protein or damage by free radicals. They are then degraded and replaced by newly synthesised proteins. Secondly, turnover helps to maintain concentrations of free amino acids both within cells and in the blood. This is important to satisfy the requirements for synthesis of essential proteins and peptides (e.g. hormones) and some small nitrogen-containing compounds that play key roles in metabolism (see Table 8.4). 

Nelson RJ, Ziegelhoffer T, Nicolet C, Werner-Washburne M, Craig EA (1992) The translation machinery and 70 kd heat shock protein cooperate in protein synthesis. Cell 71 97-105 Nissen P, Hansen J, Ban N, Moore PB, Steitz TA (2000) The structural basis of ribosome activity in peptide bond synthesis. Science 289 920-930... 

Rapid Translation of a Single Message by Polysomes Large clusters of 10 to 100 ribosomes that are very active in protein synthesis can be isolated from both eukaryotic and bacterial cells. Electron micrographs show a liber between adjacent ribosomes in the cluster, which is called a polysome (Fig. 27-27). The connecting strand... 

A pharmaceutical company is studying a new antibi otic that inhibits bacterial protein synthesis. When this antibiotic is added to an i n vitro protein synthesis system that is translating the mRNA sequence AUGUUUUUUUAG, the only product formed is the dipeptide fMet-Phe. What step in protein synthesis is most likely inhibited by the antibiotic ... 

At each stage in protein synthesis on the ribosome—-initiation, elongation, and termination—a different set of protein factors is engaged by the ribosome. Why do such protein factors, which are crucial to the translation, exist separate from the ribosome Why must they cycle on and... 

Smart, C.C. Trewavas, A.J. (1984). Abscisic-acid-induced turion formation in Spirodela polyrrhiza L. III. Specific changes in protein synthesis and translatable RNA during turion development. Plant, Cell and Environment 7, 121-32. 

SERCA pumps sequester Ca2+ in the ER lumen By maintaining appropriate Ca2+ concentrations in the ER lumen, SERCA pumps also play an essential role in protein synthesis, folding and transport of membrane and secreted proteins. This involves in particular chaperone-dependent processing and post-translational modifications which require a unique calcium rich environment. Chaperone molecules such as calreticulin and calnexin are involved in the quality control pathway in the ER (Berridge, 2002 Ellgaard and Helenius, 2003 Michalak et al., 2002). 

Gene structure and any of the processes involved in DNA expression including transcription, mRNA processing and translation and protein synthesis (Figure 2.2) can all be examined by molecular techniques. In toxicology this may include toxic effects on these processes or the role of the processes in the mechanism of toxic action. 

CODON Three contiguous nucleotides in mRNA that specify the amino acid to be inserted at a specific position in a polypeptide during translation of the 64 possible codons that are formed by the four types of nucleotides in SNA (nucleotides of adenine, guanine, cytosine, and uracil), 61 specify an amino acid and three (nonsense codons) specify no amino acid, but rather serve as termination signals in protein synthesis. 

Hydrogen bonds are not just important for small molecules. Duplex strands of DNA and RNA are held together by hydrogen bonds between complementary purine and pyrimidine bases. Because each individual bond is weak it is possible to unzip these large molecules and use the primary sequence in transcription (for sequence copying) or translation (for protein synthesis) and zip up the hydrogen bonds after the information has been accessed by transcription and translation enzymes. Transfer of encoded information can therefore occur without destroying the sequences of the parent compound. 

There are other complex issues with regard to the assessment of safety pharmacology studies. With the oligonucleotide therapeutics that modulate the translation of mRNA to proteins, like antisense/siRNA, there is a lag between administration of the drug and the pharmacologic activity that is mediated by reduction in protein levels. This lag is related to the mechanism of action and how long it takes for a reduction in protein synthesis to be reflected in reduced protein levels. Because of this lag it is probably better to... 

Messenger RNAs (mRNAs) and transfer RNAs (tRNAs) participate directly in protein synthesis. The nucleotide sequence of one of the two DNA strands in the double-helix is transcribed by RNA polymerase to produce a mRNA that is complementary to it (see Experiment 22). A portion or all of this mRNA nucleotide sequence will then serve as the template for the ribosome, which will translate the mRNA molecule into a polypeptide or protein (see Experiment 23). Messenger RNAs, then, carry information contained in the DNA into the production of protein. 

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