ArticleslgStudy

science

Klenow fragment

Klenow fragment is a science 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 Klenow fragment rather than just read about it. In short: The Klenow fragment is a large protein fragment produced when DNA polymerase I (Pol I) from E. coli is enzymatically cleaved by the protease subtilisin. First reported in 1970, it retains the 5' → 3' polymerase activity and the 3’ → 5’ exonuclease activity for removal of precoding nucleotides and proofreading, but loses its 5' → 3' exonuclease activity.

Klenow fragment — main illustration
Klenow fragment — illustration

Key takeaways

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

Reference excerpt

The Klenow fragment is a large protein fragment produced when DNA polymerase I (Pol I) from E. coli is enzymatically cleaved by the protease subtilisin. First reported in 1970, it retains the 5' → 3' polymerase activity and the 3’ → 5’ exonuclease activity for removal of precoding nucleotides and proofreading, but loses its 5' → 3' exonuclease activity. The other smaller fragment formed when DNA polymerase I from E. coli is cleaved by subtilisin retains the 5' → 3' exonuclease activity but does not have the other two activities exhibited by the Klenow fragment (i.e. 5' → 3' polymerase activity, and 3' → 5' exonuclease activity).

Research Because the 5' → 3' exonuclease activity of DNA polymerase I from E. coli makes it unsuitable for many applications, the Klenow fragment, which lacks this activity, can be very useful in research. The Klenow fragment is extremely useful for research-based tasks such as:

Synthesis of double-stranded DNA from single-stranded templates Filling in receded 3' ends of DNA fragments to make 5' overhang blunt Digesting away protruding 3' overhangs Preparation of radioactive DNA probes The Klenow fragment was also the original enzyme used for greatly amplifying segments of DNA in the polymerase chain reaction (PCR) process, before being replaced by thermostable DNA polymerases such as Taq polymerase.

The exo-Klenow fragment Just as the 5' → 3' exonuclease activity of DNA polymerase I from E.coli can be undesirable, the 3' → 5' exonuclease activity of Klenow fragment can also be undesirable for certain applications. This problem can be overcome by introducing mutations in the gene that encodes Klenow. This results in forms of the enzyme being expressed that retain 5' → 3' polymerase activity, but lack any exonuclease activity (5' → 3' or 3' → 5'). This form of the enzyme is called the exo-Klenow fragment. The exo-Klenow fragment is used in some fluorescent labeling reactions for microarray, and also in dA and dT tailing, an important step in the process of ligating DNA adapters to DNA fragments, frequently used in preparing DNA libraries for Next-Gen sequencing. (for instance see [1])

From other polymerases The term Klenow fragment is also applied more generally to any DNA polymerase I with the 5'-3'-exo activity removed. Ones that see practical use include:

The Klenow fragment of Geobacillus stearothermophilus (Bst) Pol I. It has a strand displacement activity which allows for use in isothermal amplification without the necessity of denaturation of the DNA in a thermocycler. The exonuclease activity is deleted for higher yield. The Klenow fragment of Taq polymerase, more properly known as KlenTaq or Stoffel fragment.

References

External links Klenow+Fragment at the U.S. National Library of Medicine Medical Subject Headings (MeSH) Diagram at vivo.colostate.edu

Illustrations

Klenow fragment: Functional domains in the Klenow Fragment (left) and DNA Polymerase I (PDB).
Functional domains in the Klenow Fragment (left) and DNA Polymerase I (PDB).

Worked examples

Example 1 — a first encounter with Klenow fragment

Start with the simplest possible case. Write down what Klenow fragment claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Klenow fragment 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 Klenow fragment 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 Klenow fragment

In research
Klenow fragment appears in science 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 Klenow fragment 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
Klenow fragment is common in secondary-school and first-year university syllabi. It links to neighbouring topics DNA replication, so understanding it makes those chapters shorter.
In everyday life
Look for Klenow fragment 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.
Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Klenow fragment” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Klenow fragment in 20 minutes

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

Frequently asked questions

What is Klenow fragment in simple terms?

The Klenow fragment is a large protein fragment produced when DNA polymerase I (Pol I) from E. coli is enzymatically cleaved by the protease subtilisin. First reported in 1970, it retains the 5' → 3' polymerase activity and the 3’ → 5’ exonuclease activity for removal of precoding nucleotides and p…

Why does Klenow fragment matter?

Because it connects several science 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 Klenow fragment?

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 Klenow fragment.

Tags

  • DNA replication

Keep exploring