Ribosomes tRNA and

When any of the three stop (termination or nonsense) codons moves into the A site, peptidyl transferase (with the help of release fector) hydrolyzes the completed protein from the final tRNA in the P site. The mRNA, ribosome, tRNA, and factors can aU be reused for additional protein synthesis,... 

The ribosome recycling factor (RRF) is a 21 kDa protein which is involved in the termination step of protein biosynthesis and catalyses the breakdown of the post termination complex into ribosome, tRNA and mRNA. The solution structure of RRF from the hyperthermophilic bacterium Aquifex aeolicus (7 opt = 85°Q was determined by heteronuclear multidimensional NMR spectroscopy, whereas the backbone NMR assignment was recently carried out for RRF from Themotoga maritima and Thermus thermophilus ... 

Matrix. This large internal space contains a highly concentrated mixture of hundreds of enzymes, including those required for the oxidation of pyruvate and fatty acids for the citric acid cycle. The matrix also contains several identical copies of the mitochondrial DNA genome, special mitochondrial ribosomes, tRNAs, and various enzymes required for expression of mitochondrial genes. 

The lytic cycle Is somewhat more complicated for DNA viruses that Infect eukaryotic cells. In most such viruses, the DNA genome Is transported (with some associated proteins) Into the cell nucleus. Once Inside the nucleus, the viral DNA Is transcribed Into RNA by the host s transcription machinery. Processing of the viral RNA primary transcript by hostcell enzymes 3delds viral mRNA, which Is transported to the cytoplasm and translated Into viral proteins by host-cell ribosomes, tRNA, and translation factors. The viral proteins are then transported back Into the nucleus, where some of them either replicate the viral DNA directly or direct cellular proteins to replicate the viral DNA, as In the case of SV40 discussed In the last section. Assembly of the capsid proteins with the newly replicated viral DNA occurs in the nucleus, 3deldlng hundreds to thousands of progeny virions. 

Host-cell ribosomes, tRNAs, and translation factors are used In the synthesis of all viral proteins In Infected cells. 

It has been known for some time that tetracyclines are accumulated by bacteria and prevent bacterial protein synthesis (Fig. 4). Furthermore, inhibition of protein synthesis is responsible for the bacteriostatic effect (85). Inhibition of protein synthesis results primarily from dismption of codon-anticodon interaction between tRNA and mRNA so that binding of aminoacyl-tRNA to the ribosomal acceptor (A) site is prevented (85). The precise mechanism is not understood. However, inhibition is likely to result from interaction of the tetracyclines with the 30S ribosomal subunit because these antibiotics are known to bind strongly to a single site on the 30S subunit (85). 

In the cytoplasm, the mRNA attaches to a ribosome and acts as a template for the construction of a protein with the proper amino acid sequence (a process known as translation ). Single amino acids are brought to the ribosome by transfer RNA molecules (tRNA) and added to the growing amino acid chain in the order instructed by the mRNA. Each time a nucleotide is added to the growing RNA strand, one molecule of ATP is broken down to ADP. Each time a tRNA binds an amino acid and each time the amino acid is added to the protein, additional ATP is broken down to ADP. Because proteins can contain many hundreds of amino acids, the cell must expend the energy in 1,000 or more ATP molecules to build each protein molecule. 

Mitochondria are unique organelles in man and higher animals in that they contain their own genome. Mitochondrial DNA (mtDNA) in humans is a small (16.5 kb), circular genome that encodes only 13 proteins, 22 transfer RNA (tRNA), and 2 ribosomal RNA (rRNA) molecules. mtDNA is inherited only from the mother and is present in multiple copies within one mitochondrion. 

In all prokaryotic and eukaryotic organisms, three main classes of RNA molecules exist messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA... 

Figure 38-8. Diagrammatic representation of the peptide elongation process of protein synthesis. The small circles labeled n - 1, n, n -I-1, etc, represent the amino acid residues of the newly formed protein molecule. EFIA and EF2 represent elongation factors 1 and 2, respectively. The peptidyl-tRNA and aminoacyl-tRNA sites on the ribosome are represented by P site and A site, respectively.

Nucleic acids can contain of any one of three kinds of pyrimidine ring systems (uracil, cytosine, or thymine) or two types of purine derivatives (adenine or guanine). Adenine, guanine, thymine, and cytosine are the four main base constituents found in DNA. In RNA molecules, three of these four bases are present, but with thymine replaced by uracil to make up the fourth. Some additional minor derivatives are found in messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), particularly the N4,N4-dimethyladenine and N7-methylguanine varieties. 

The answer is b. (Hardman, p 1131.) Chloramphenicol inhibits protein synthesis in bacteria and, to a lesser extent, in eukaryotic cells. The drug binds reversibly to the. 505 ribosomal subunit and prevents attachment of aminoacybtransfer RNA (tRNA) to its binding site. The amino acid substrate is unavailable for peptidyl transferase and peptide bond formation. 

The next process is similar in both eukaryotes and prokaryotes, and involves the translation of mRNA molecules into polypeptides. This procedure involves many enzymes and two further types of RNA transfer RNA (tRNA) and ribosomal RNA (rRNA). There is a specific tRNA for each of the amino acids. These molecules are involved in the transportation and coupling of amino acids into the resulting... 

The three types of RNA are transfer (tRNA), ribosomal (rRNA), and messenger (mRNA). 

Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemical cousins of... 

Wittmann-Liebold, B. (1980b). In Genetics and Evolution of RNA Polymerase, tRNA, and Ribosomes (S. Osawa, H. Ozeki, H. Uchida, and T. Yura, eds.), p. 639. Univ. of Tokyo Press, Tokyo. 

EF-G and the ribosome recycling factor (RRF) catalyze dissociation of the tRNA and the mRNA from the ribosome as well as dissociation of the two ribosomal subunits. Consequently, the ribosome as well as the mRNA are prepared for a new round of protein synthesis. 

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