<P> Viruses can be present in humans due to direct infection or co-infections which makes diagnosis difficult using classical techniques and can result in an incorrect prognosis and treatment . The use of qPCR allows both the quantification and genotyping (characterization of the strain, carried out using melting curves) of a virus such as the Hepatitis B virus . The degree of infection, quantified as the copies of the viral genome per unit of the patient's tissue, is relevant in many cases; for example, the probability that the type 1 herpes simplex virus reactivates is related to the number of infected neurons in the ganglia . This quantification is carried out either with reverse transcription or without it, as occurs if the virus becomes integrated in the human genome at any point in its cycle, such as happens in the case of HPV (human papillomavirus), where some of its variants are associated with the appearance of cervical cancer . </P> <P> qPCR is used to evaluate biodegradation potential or activity in contaminated groundwater . qPCR is used to detect and quantify bacteria such as Dehalococcoides mccartyi as well as vinyl chloride reductase functional genes essential to the biodegradation of chlorinated solvents including trichloroethene and tetrachloroethylene . qPCR is also commonly used to quantify functional genes involved in the biodegradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) and evaluate monitored natural attenuation (MNA) or other remedial methods at impacted petroleum hydrocarbon sites . Reverse transcriptase quantitative polymerase chain reaction (RT - qPCR), which is based on the analysis of RNA rather than DNA, is used to quantify gene expression and identify biodegradation activity . </P>

10. what is the four-step process of an enzyme at work