Breaking the Bond: The PCR Denaturation Step

If the goal of the first step is to provide a "pattern" for the new DNA, then the original molecule must be split. If it is split, then it exists as two individual single-strand templates.

If the genetic information is "locked" inside the double helix, then it must be "unlocked" to be read. If heating the sample to 95°C separates the strands, then the information is finally accessible for the rest of the PCR process.

If the process is a "Polymerase Chain Reaction," then the name highlights the importance of the enzyme that builds the DNA chains.

If every new cycle starts with double-stranded DNA (either the original or the newly made copies), then the strands must be opened every time. If they aren't opened in every cycle, then the process stops after one round.

If the goal is to copy DNA, the steps must follow a logical order: first open the DNA (denaturation), then let primers land (annealing), then build the new strand (extension).

If standard proteins (like those in humans) unfold and "die" at high temperatures, then they would be useless after the first heating cycle. If the enzyme is from a heat-loving bacteria (like Taq), then it can survive the 95°C heat.

If the covalent bonds are not broken, the chemical identity of the strands remains the same. If the temperature drops, the bases will naturally seek their partners and re-form the double helix; therefore, the change is reversible.

If G-C pairs are held by three bonds and A-T by two, then a G-C heavy sequence is physically "tighter." If it is tighter, then it requires more time or a higher temperature to ensure every bond is broken.

If the reaction is to take place, it needs the starting material (template) and the energy to open it. If the chemicals must be able to move and collide, then they must be in a liquid buffer; oxygen and vacuums are not required.

If the DNA remains a closed double helix, then the primers cannot reach the internal bases to start the copying process. If the primers cannot bind, then the polymerase has nowhere to start, and no DNA is produced.

If the hydrogen bonds between complementary bases are broken by high heat, then the two strands of the double helix can no longer stay together. If they cannot stay together, then the DNA becomes single-stranded.

If DNA is designed to stay stable and closed at normal body temperatures to protect our genetic code, then 37°C is not enough energy to break the bonds. If the bonds don't break, then denaturation fails.

If Guanine and Cytosine share three hydrogen bonds while Adenine and Thymine share only two, then the G-C pairs provide more "glue." If there is more glue, then more thermal energy (heat) is needed to pull them apart.

If the sugar-phosphate backbone is held together by covalent bonds, then it requires much more energy to break than the hydrogen bonds between bases. If the heat only reaches 95°C, then only the weaker hydrogen bonds will break.

If the PCR process requires precise, repeating cycles of heating and cooling, then a machine designed to cycle those temperatures is known as a thermal cycler.

If a living cell uses the protein helicase to "unzip" DNA at body temperature, then PCR uses thermal energy (heat) to achieve that same unzipping effect in a test tube.

If the temperature is raised to 95°C, then the double helix unwinds and the hydrogen bonds snap, resulting in separated strands. Primers and polymerase do not function until the temperature is lowered in later steps.

If the heat must be high enough to vibrate the hydrogen bonds until they break but not so high that it destroys the covalent backbone, then a range near the boiling point of water (94-98°C) is required.

If the nitrogenous bases are held together by weak electrical attractions rather than strong shared-electron bonds, then those weak links are called hydrogen bonds.

If the PCR process requires the DNA to be open so that primers can attach, then the strands must be separated before any copying can begin. If separation happens first, then denaturation is the initial step.