chemistry

Polymerase chain reaction inhibitors

Polymerase chain reaction inhibitors is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polymerase chain reaction inhibitors rather than just read about it. In short: PCR inhibitors are any factor which prevent the amplification of nucleic acids through the polymerase chain reaction (PCR). PCR inhibition is the most common cause of amplification failure when sufficient copies of DNA are present.

Key takeaways

Polymerase chain reaction inhibitors belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polymerase chain reaction inhibitors to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polymerase chain reaction inhibitors from memory before moving on to harder problems.

Reference excerpt

PCR inhibitors are any factor which prevent the amplification of nucleic acids through the polymerase chain reaction (PCR). PCR inhibition is the most common cause of amplification failure when sufficient copies of DNA are present. PCR inhibitors usually affect PCR through interaction with DNA or interference with the DNA polymerase. Inhibitors can escape removal during the DNA purification procedure by binding directly to single or double-stranded DNA. Alternatively, by reducing the availability of cofactors (such as Mg2+) or otherwise interfering with their interaction with the DNA polymerase, PCR is inhibited. In a multiplex PCR reaction, it is possible for the different sequences to suffer from different inhibition effects to different extents, leading to disparity in their relative amplifications.

Types of inhibitors Inhibitors may be present in the original sample, such as blood, fabrics, tissues and soil but may also be added as a result of the sample processing and DNA extraction techniques used. Excess salts including KCl and NaCl, ionic detergents such as sodium deocycholate, sarkosyl and SDS, ethanol, isopropanol and phenol among others, all contribute via various inhibitory mechanisms, to the reduction of PCR efficiency.

Quantifying extent of inhibition In order to try to assess the extent of inhibition that occurs in a reaction, a control can be performed by adding a known amount of a template to the investigated reaction mixture (based on the sample under analysis). By comparing the amplification of this template in the mixture to the amplification observed in a separate experiment in which the same template is used in the absence of inhibitors, the extent of inhibition in the investigated reaction mixture can be inferred. Of course, if any part of the inhibition occurring in the sample-derived reaction mixture is sequence-specific, then this method will yield an underestimate of the inhibition as it applies to the investigate sequence(s).

Preventing PCR inhibition

Sample collection The method of sample acquisition can be refined to avoid unnecessary collection of inhibitors. For example, in forensics, swab-transfer of blood on fabric or saliva on food, may prevent or reduce contamination with inhibitors present in the fabric or food.

DNA purification Techniques exist and kits are commercially available to enable extraction of DNA to the exclusion of some inhibitors.

PCR reaction components As well as methods for the removal of inhibitors from samples before PCR, some DNA polymerases offer varying resistance to different inhibitors and increasing the concentration of the chosen DNA polymerase also confers some resistance to polymerase-targeted inhibitors. For PCR based on blood samples, the addition of bovine serum albumin reduces the effect of some inhibitors on PCR.

Worked examples

Example 1 — a first encounter with Polymerase chain reaction inhibitors

Start with the simplest possible case. Write down what Polymerase chain reaction inhibitors claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polymerase chain reaction inhibitors before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polymerase chain reaction inhibitors ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polymerase chain reaction inhibitors

In research: Polymerase chain reaction inhibitors appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polymerase chain reaction inhibitors in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polymerase chain reaction inhibitors is common in secondary-school and first-year university syllabi. It links to neighbouring topics DNA, Polymerase chain reaction, so understanding it makes those chapters shorter.
In everyday life: Look for Polymerase chain reaction inhibitors outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Polymerase chain reaction inhibitors in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polymerase chain reaction inhibitors means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Polymerase chain reaction inhibitors out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polymerase chain reaction inhibitors in simple terms?

Why does Polymerase chain reaction inhibitors matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polymerase chain reaction inhibitors?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polymerase chain reaction inhibitors.