Diseases, Conditions, Syndromes

Neurological symptoms described in children with COVID-19

Children with COVID-19 may present with new neurological symptoms involving the central and peripheral nervous systems, and splenial changes on imaging, according to a study published online July 1 in JAMA Neurology.

Diseases, Conditions, Syndromes

'The tip of the iceberg': Virologist discusses COVID-19

As of March 20, more than 8,700 people worldwide had died of COVID-19, the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Caltech trustee David Ho (BS '74) of the Aaron Diamond AIDS Research ...

HIV & AIDS

Cellphone technology developed to detect HIV

The management of human immunodeficiency virus 1 (HIV), an autoimmune disorder that cripples the immune system by attacking healthy cells, remains a major global health challenge in developing countries that lack infrastructure ...

Diseases, Conditions, Syndromes

New type of MRSA in hospitalized patients probably of animal origin

A distinctly new type of methicillin resistant Staphylococcus aureus (MRSA) that is not detected by traditional genetic screening methods has been discovered in patients in Irish hospitals according to research to be published ...

Medical research

New method performs coronavirus test 10 times faster

Currently, it takes more than two hours to perform and evaluate a test for SARS-CoV-2—meaning that a laboratory can test only a very limited number of people per day. In a study with several cooperation partners, cell biologists ...

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Polymerase chain reaction

In molecular biology, the polymerase chain reaction (PCR) is a technique to amplify a single or few copies of a piece of DNA across several orders of magnitude, generating millions or more copies of a particular DNA sequence. The method relies on thermal cycling, consisting of cycles of repeated heating and cooling of the reaction for DNA melting and enzymatic replication of the DNA. Primers (short DNA fragments) containing sequences complementary to the target region along with a DNA polymerase (after which the method is named) are key components to enable selective and repeated amplification. As PCR progresses, the DNA generated is itself used as a template for replication, setting in motion a chain reaction in which the DNA template is exponentially amplified. PCR can be extensively modified to perform a wide array of genetic manipulations.

Almost all PCR applications employ a heat-stable DNA polymerase, such as Taq polymerase, an enzyme originally isolated from the bacterium Thermus aquaticus. This DNA polymerase enzymatically assembles a new DNA strand from DNA building blocks, the nucleotides, by using single-stranded DNA as a template and DNA oligonucleotides (also called DNA primers), which are required for initiation of DNA synthesis. The vast majority of PCR methods use thermal cycling, i.e., alternately heating and cooling the PCR sample to a defined series of temperature steps. These thermal cycling steps are necessary to physically separate the strands (at high temperatures) in a DNA double helix (DNA melting) used as the template during DNA synthesis (at lower temperatures) by the DNA polymerase to selectively amplify the target DNA. The selectivity of PCR results from the use of primers that are complementary to the DNA region targeted for amplification under specific thermal cycling conditions.

Developed in 1984 by Kary Mullis, PCR is now a common and often indispensable technique used in medical and biological research labs for a variety of applications. These include DNA cloning for sequencing, DNA-based phylogeny, or functional analysis of genes; the diagnosis of hereditary diseases; the identification of genetic fingerprints (used in forensic sciences and paternity testing); and the detection and diagnosis of infectious diseases. In 1993 Mullis was awarded the Nobel Prize in Chemistry for his work on PCR.

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