From the article This Time, It’s Personal.

Freshman biology textbooks teach that RNA molecules are made using DNA as a template and that those messenger RNA molecules then move to large protein complexes called ribosomes that can make new proteins using the RNA as an instruction manual. The process is compared with a message in words. The messenger RNA is said to be transcribed from the DNA template, and the ribosomes are said to translate the message from the messenger RNA into proteins. Although the DNA to RNA to protein concept remains true from a fundamental standpoint, it has been derided as “the central dogma of molecular biology” because the situation is more complicated than that.

Parts of messenger RNA molecules may be cut out before they reach ribosomes, and sometimes messenger RNA can be prevented from reaching the ribosomes at all. Therefore, scientists cannot measure protein levels while ignoring messenger RNA levels. The complexity of the situation is one reason that measuring messenger RNA levels at various time periods is important.

The polymerase chain reaction (PCR) has revolutionized biology, medicine and forensics. It mimics DNA replication as it occurs in cells. Short DNA sequences called primers bind to the DNA template, and the DNA goes through heat-up and cool-down temperature cycles. A DNA polymerase from Thermus aquaticus (Taq) then makes more DNA with each cooldown.