Sarmila Tandukar, Parasitology Research - Abstract This study aimed to determine the prevalence of intestinal parasites and its associated risk factors among school-going children in Kathmandu, Nepal. Between August and Septembera total of stool samples were collected from children at five public schools. The collected samples were subjected to formol-ether concentration, followed by conventional microscopic examination for intestinal parasites.
History[ edit ] Since the introduction of Northern blot init had been used extensively for RNA quantification despite its shortcomings: Made it theoretically possible to detect the transcripts of practically any gene  Enabled sample amplification and eliminated the need for abundant starting material required when using northern blot analysis   Provided tolerance for RNA degradation as long as the RNA spanning the primer is intact  One-step RT-PCR vs.
The difference between the two approaches lies in the number of tubes used when performing the procedure. On the other hand, the two-step reaction requires that the reverse transcriptase reaction and PCR amplification be performed in separate tubes.
The one-step approach is thought to minimize experimental variation by containing all of the enzymatic reactions in a single environment. However, the starting RNA templates are prone to degradation in the one-step approach, and the use of this approach is not recommended when repeated assays from the same sample is required.
Additionally, one-step approach is reported to be less accurate compared to the two-step approach. It is also the preferred method of analysis when using DNA binding dyes such as SYBR Green since the elimination of primer-dimers can be achieved through a simple change in the melting temperature.
The disadvantage of the two-step approach is susceptibility to contamination due to more frequent sample handling. Relative quantifications of RT-PCR involves the co-amplification of an internal control simultaneously with the gene of interest.
The internal control is used to normalize the samples. Once normalized, a direct comparison of relative transcript abundances across multiple samples of mRNA can be made.
One precaution to note is that the internal control must be chosen so that it is not affected by the experimental treatment. The expression level should be constant across all samples and with the mRNA of interest for the results to be accurate and meaningful.
Because the quantification of the results are analyzed by comparing the linear range of the target and control amplification, it is crucial to take into consideration the starting target molecules concentration and their amplification rate prior to starting the analysis.
The results of the analysis are expressed as the ratios of gene signal to internal control signal, which the values can then be used for the comparison between the samples in the estimation of relative target RNA expression. It is important for the design of the synthetic RNA be identical in sequence but slightly shorter than the target RNA for accurate results.
Then, a concentration curve of the competitor RNA is produced and it is used to compare the RT-PCR signals produced from the endogenous transcripts to determine the amount of target present in the sample.
Once the reaction is complete, the results are compared to an external standard curve to determine the target RNA concentration. In comparison to the relative and competitive quantification methods, comparative RT-PCR is considered to be the more convenient method to use since it does not require the investigator to perform a pilot experiment; in relative RT-PCR, the exponential amplification range of the mRNA must be predetermined and in competitive RT-PCR, a synthetic competitor RNA must be synthesized.
Not only is real-time RT-PCR now the method of choice for quantification of gene expression, it is also the preferred method of obtaining results from array analyses and gene expressions on a global scale.
All of these probes allow the detection of PCR products by generating a fluorescent signal. The intensity of the fluorescence increases as the PCR products accumulate. This technique is easy to use since designing of probes is not necessary given lack of specificity of its binding. However, since the dye does not discriminate the double-stranded DNA from the PCR products and those from the primer-dimers, overestimation of the target concentration is a common problem.
Where accurate quantification is an absolute necessity, further assay for the validation of results must be performed. TaqMan probes are oligonucleotides that have a fluorescent probe attached to the 5' end and a quencher to the 3' end. During PCR amplification, these probes will hybridize to the target sequences located in the amplicon and as polymerase replicates the template with TaqMan bound, it also cleaves the fluorescent probe due to polymerase 5'- nuclease activity.
Because the close proximity between the quench molecule and the fluorescent probe normally prevents fluorescence from being detected through FRET, the decoupling results in the increase of intensity of fluorescence proportional to the number of the probe cleavage cycles.
Although well-designed TaqMan probes produce accurate real-time RT-PCR results, it is expensive and time-consuming to synthesize when separate probes must be made for each mRNA target analyzed.
Similar to the TaqMan probes, Molecular Beacons also make use of FRET detection with fluorescent probes attached to the 5' end and a quencher attached to the 3' end of an oligonucleotide substrate.
However, whereas the TaqMan fluorescent probes are cleaved during amplification, Molecular Beacon probes remain intact and rebind to a new target during each reaction cycle. When free in solution, the close proximity of the fluorescent probe and the quencher molecule prevents fluorescence through FRET.
However, when Molecular Beacon probes hybridize to a target, the fluorescent dye and the quencher are separated resulting in the emittance of light upon excitation.
The Scorpion probes, like Molecular Beacon, will not be fluorescent active in an unhybridized state, again, due to the fluorescent probe on the 5' end being quenched by the moiety on the 3' end of an oligonucleotide.
With Scorpions, however, the 3' end also contains sequence that is complementary to the extension product of the primer on the 5' end. When the Scorpion extension binds to its complement on the amplicon, the Scorpion structure opens, prevents FRET, and enables the fluorescent signal to be measured.A real-time polymerase chain reaction (Real-Time PCR), also known as quantitative polymerase chain reaction (qPCR), is a laboratory technique of molecular biology based on the polymerase chain reaction (PCR).
It monitors the amplification of a targeted DNA molecule during the PCR, i.e. in real-time, and not at its end, as in conventional PCR. Real-time PCR can be used quantitatively. Quantitative PCR (qPCR), also known as real-time PCR, puts a spin on this process by monitoring the reaction in real time using fluorescence to label the copies of DNA as they are produced.
During qPCR, the amount of fluorescence that is measured is directly proportional to the amount of DNA being produced – the brighter it glows, the more. One-step vs. Two-step RT-qPCR.
RT-qPCR can be performed in a one-step or a two-step assay (Figure1, Table 1).
One-step assays combine reverse transcription and PCR in a single tube and buffer, using a reverse transcriptase along with a DNA polymerase. One-step RT-qPCR only utilizes sequence-specific primers.
qPCR; Quantitative Analysis of DNA With the development of thermal cyclers incorporating fluorescent detection, the polymerase chain reaction assay (PCR) has new, innovative applications.
In routine PCR, the critical result is the final quantity of amplicon generated from the assay. The reverse transcription - polymerase chain reaction (RT-PCR) is the most sensitive method for the detection of low abundance mRNA, often obtained from limited tissue samples.
INTRODUCTION. The polymerase chain reaction (PCR) is a sensitive technique by which a single DNA molecule can serve as a template for amplification (Azevedo et al.