Question

Which type of restriction enzymes are used in genetic engineering work

• A. Type I
• B. Type II
• C. Type III
• D. Type IV

Hint:

• Type II Restriction Enzymes} are most widely used in genetic engineering because:
  • They recognize specific DNA sequences (restriction sites).
  • They cleave DNA at or very near these specific sites in a predictable manner.
  • They generally require only Mg\(^{2+}\) for activity (simpler cofactor requirements).
• Type I and Type III enzymes have cleavage sites distant from their recognition sites, making them less useful for precise DNA manipulation.

Answer 1

The Correct Option is B

Restriction enzymes (or restriction endonucleases) are enzymes that cut DNA at or near specific recognition nucleotide sequences known as restriction sites. They are crucial tools in molecular biology and genetic engineering. There are several types of restriction enzymes, classified based on their structure, cofactor requirements, and cleavage properties:

• Type I Restriction Enzymes: Complex, multisubunit enzymes. They recognize specific DNA sequences but cleave DNA at random sites, often far from the recognition sequence. They require ATP, S-adenosylmethionine (SAM), and Mg\(^{2+}\) for activity. Due to their non-specific cleavage site relative to the recognition site, they are generally not useful for routine genetic engineering work that requires precise cutting.
• Type II Restriction Enzymes: These are the most commonly used restriction enzymes in molecular cloning and genetic engineering. They recognize specific (often palindromic) DNA sequences (typically 4-8 base pairs long) and cleave the DNA at or very near these recognition sites in a predictable and reproducible manner. They usually require only Mg\(^{2+}\) as a cofactor. Their predictable cleavage makes them ideal for creating specific DNA fragments. Examples: EcoRI, HindIII, BamHI.
• Type III Restriction Enzymes: Complex enzymes that recognize specific DNA sequences but cleave DNA at a defined distance (e.g., 24-26 bp) away from the recognition site. They require ATP and Mg\(^{2+}\), and SAM can stimulate activity. Their cleavage pattern is less straightforward than Type II, making them less commonly used in routine cloning.
• Type IV Restriction Enzymes: Recognize modified (e.g., methylated) DNA and cleave it.
• Type V Restriction Enzymes: Utilize guide RNAs (gRNAs) to target specific DNA sequences for cleavage (e.g., Cas9 from CRISPR-Cas system).

For most genetic engineering applications that require precise and predictable cutting of DNA at specific sites (e.g., for cloning, DNA mapping, RFLP analysis), Type II restriction enzymes are the workhorses. \[ \boxed{\text{Type II}} \]