RNA copy

If DNA from two different species are mixed, denatured, and allowed to cool slowly so that reannealing can occur, artificial hybrid duplexes may form, provided the DNA from one species is similar in nucleotide sequence to the DNA of the other. The degree of hybridization is a measure of the sequence similarity or relatedness between the two species. Depending on the conditions of the experiment, about 25% of the DNA from a human forms hybrids with mouse DNA, implying that some of the nucleotide sequences (genes) in humans are very similar to those in mice. Mixed RNA DNA hybrids can be created in vitro if single-stranded DNA is allowed to anneal with RNA copies of itself, such as those formed when genes are transcribed into mRNA molecules. 

These vectors typically have a polylinker adjacent to the SPG promoter. Successive rounds of transcription initiated by SPG RNA polymerase at its promoter lead to the production of multiple RNA copies of any DNA inserted at the polylinker. Before transcription is initiated, the circular expression vector is linearized by a single cleavage at or near the end of the insert so that transcription terminates at a fixed point. 

Whereas DNA has a single role as the storehouse of genetic information, RNA plays many roles in the operation of a cell. There are several different types of RNA, each having its own function. The principal job of RNA is to provide the information needed to synthesize proteins. Protein synthesis requires several steps, each assisted by RNA. One type of RNA copies the genetic information from DNA and carries this blueprint out of the nucleus and into the cytoplasm, where construction of the protein takes place. The protein is assembled on the surface of a ribosome, a cell component that contains a second type of RNA. The protein is consfructed by sequential addition of amino acids in the order specified by the DNA. The individual amino acids are carried to the growing protein chain by yet a third type of RNA. The details of protein synthesis are well understood, but the process is much too complex to be described in an introductoiy course in chemistry. 

Transcription The synthesis of an RNA copy from a sequence of DNA (i.e., a gene) the first step in gene expression (see also translation). 

Probability of progression to acquired immune deficiency syndrome (AIDS) is related to RNA viral load in one study, 5-year progression rates to AIDS were 8% and 62% for RNA copies per milliliter of less than 4,530 and greater than 36,270, respectively. The mortality rates were 5% and 49%, respectively. 

An amplification reaction that is used to amplify target RNA or denatured DNA is called the transcription-based amplification system (TAS). This technique involves using an enzyme called reverse transcriptase and a primer with sequence complementary to the sample target RNA molecule in order to synthesize a complementary DNA (cDNA) copy of the sample target RNA. After denaturation to separate the strands, another primer and additional reverse transcriptase are added to synthesize a double-stranded cDNA molecule. Since the first primer has also an RNA polymerase binding site, it can, in the presence of T7 RNA polymerase, amplify the double-stranded cDNA to produce 10 to 100 copies of RNA. The cycle of denaturation, synthesis of cDNA, and amplification to produce multiple RNA copies is repeated. With as few as four cycles, a 2- to 5-millionfold amplification of the original sample RNA target is possible. However, the time required to achieve a millionfold amplification is approximately 4 hours, which is the same amount of time required by PCR. The TAS requires, however, the addition of two enzymes at each cycle and, as such, can be cumbersome. 

Transcription is the process by which RNA copies of the genes are synthesized as the first step leading to gene expression. 

C. mRNA represents an RNA copy of a gene, which directs synthesis of a specific protein by the ribosomes. 

Figure 1.1 The structure of DNA is illustrated here. DNA is the genetic material of the cell. Through the processes of transcription and translation, the DNA sequence is used to produce first an RNA copy of the gene and then a protein based on the gene sequence.

Messenger ribonucleic acid (mRNA)—Messenger RNA copy of a gene used to make a protein in a cell it is complementary to and will bind to the DNA gene. 

HIV PR inhibitors with acceptable oral availability and pharmacokinetic properties offer great promise for the treatment of HIV infection and AIDS. Efficacy studies of indinavir, ritonavir, or nelfinavir using plasma viral RNA as a marker have demonstrated up to three log reductions in RNA copy numbers that are... 

The sequence of the bases contains coded information for the synthesis of proteins. These sequences are transcribed into an RNA copy of the sequence messenger RNA (mRNA). The mRNA is translated in the cytoplasm. The DNA also encodes structural RNAs, with functions in transcription of the DNA, processing of the transcripts and translation of the transcripts. The genetic code shown in Table 8.2.1 is simple, but efficient. At each nucleotide position, there are only four possibilities A,... 

RNA copies of recombinant viruses are produced in cells containing a helper virus and packaged into viral particles. 

The presence of RNA in the cytoplasm had been linked to protein synthesis by experiments done in the early 1940s. After the discovery of the double helix, the concept followed quickly that DNA was the master "blueprint" from which secondary blueprints or transcripts of RNA could be copied. The RNA copies, later identified as messenger RNA (mRNA), provided the genetic information for specifying protein sequence. The flow of information from DNA to RNA to proteins could be symbolized as in Eq. 26-1. 

The first replicative units must have possessed considerably less information than the RNA viruses, which work with an optimized RNA-copying machinery. In the absence of efficiently adapted enzymes the accuracy of reproduction depends solely on the stability of the base pairs. Under these conditions the GC pair has a selective advantage over the AU pair of a factor of about 10. Model experiments show that for GC-rich polynucleotides the error rate per nucleotide can hardly be reduced below a value of 10-2. The first genes must accordingly have been polynucleotides with a chain length around 100 bases or less. 

Fig. 3. A transcription bubble. The DNA double helix Is unwound and RNA polymerase then synthesizes an RNA copy of the DNA template strand. The nascent RNA transiently forms an RNA-DNA hybrid helix but then peels away from the DNA which Is subsequently rewound into a helix once more.

The large number of steps involved in extracting the information contained in DNA can be divided into two conceptual categories called transcription and translation. Briefly, in transcription a cell makes an RNA copy of a small portion of its DNA (termed a gene) that... 

A stretch of DNA containing the coding information of a protein and the regulatory sequences required for its expression is known as the gene for the protein. Since all the regulatory sequences do not appear in the RNA copy of the gene, the RNA copy is always smaller than the gene from which it is transcribed. 

Figure 30.1 DNA array methodology to study the presence of sequence types in the environment. These experiments are based on previous knowledge of the sequence types in the area of interest (1) and their phylogenetic relationships (2). Arrays are spotted with DNA or oligonucleotide sequences of interest, indicated with a P (3) and hybridized with labeled DNA or cDNA (RNA copy) (4). The hybridization pattern is interpreted in terms of the phylogenetic relationship of the array probes with signal (5).

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