Question

Which of the following statements regarding restriction enzymes used in recombinant DNA technology is correct

• A. Type I restriction enzyme is a DNA restriction enzyme which cleaves DNA at defined positions close to or within the recognition site
• B. Type II restriction enzyme is a DNA restriction enzyme which cleaves DNA at defined positions close to or within the recognition site.
• C. Both cleaves DNA at defined positions close to or within the recognition site.
• D. Both cleaves DNA at defined positions far from the recognition site

Hint:

Remember: \textbf{Type II = T}wo things together. The recognition and cleavage sites are together (close or within). This is why they are the primary \textbf{T}ool of recombinant DNA technology.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Restriction enzymes (or restriction endonucleases) are enzymes that cut DNA at specific sequences. They are classified into several types based on their structure, cofactor requirements, and cleavage properties. Recombinant DNA technology almost exclusively uses Type II enzymes because of their predictable cleavage pattern.
Step 2: Detailed Explanation:
Let's review the properties of Type I and Type II restriction enzymes:
Type I Restriction Enzymes: These are complex, multi-subunit enzymes. They recognize a specific DNA sequence but cleave the DNA at a random, non-specific site far away from the recognition sequence (often 1000 bp or more). Because the cut site is unpredictable, they are not useful for precise DNA manipulation in genetic engineering.
Type II Restriction Enzymes: These are simpler enzymes that are the workhorses of molecular biology (e.g., EcoRI, HindIII, BamHI). Their key property is that they recognize a specific (usually palindromic) DNA sequence and cleave the DNA at a defined position either within or very close to that same recognition site. This predictable and precise cutting is essential for creating specific DNA fragments for cloning.
Evaluating the statements:
Statement 1 is incorrect. It describes Type II enzymes but calls them Type I.
Statement 2 is correct. It accurately describes the key feature of Type II enzymes that makes them useful for recombinant DNA technology.
Statement 3 is incorrect because Type I enzymes do not cleave near the recognition site.
Statement 4 is incorrect because Type II enzymes do not cleave far from the recognition site.
Step 3: Final Answer:
The correct statement is the one that accurately describes Type II restriction enzymes.