Restriction Enzymes (Restriction Endonucleases): Enzymes that recognize specific DNA sequences (restriction sites) and cleave DNA at or near these sites. They are essential tools in genetic engineering.
Exonucleases: Enzymes that hydrolyze nucleotides from the terminal ends (5’ or 3’) of DNA or RNA molecules, removing nucleotides sequentially from the ends.
Endonucleases: Enzymes that recognize specific internal DNA sequences (restriction sites) and cleave phosphodiester bonds within the DNA molecule, creating fragments with either sticky or blunt ends.
Type I Restriction Enzymes: Multifunctional enzymes with both restriction and modification activities, cleaving DNA approximately 1000 bp away from recognition sites, requiring ATP, SAM, and Mg²⁺.
Type II Restriction Enzymes: The most widely used in laboratories; recognize palindromic sequences and cleave within or at the recognition site, requiring only Mg²⁺, and do not need ATP. They produce predictable sticky or blunt ends.
1. What is a restriction enzyme?
2. What is the basis for the naming convention of restriction endonucleases like EcoRI or HindIII?
3. What is the primary purpose of classifying restriction enzymes into different types?
Restriction Enzymes — types?
Type I, II, and III, differ in recognition and cleavage.
Nomenclature system — basis?
Organism name + discovery order (Roman numerals).
Type II enzymes — recognition?
Recognize palindromic sequences and cut within or at recognition site.
Restriction enzyme cleavage — types?
Sticky ends (overhangs) or blunt ends.
Applications of restriction enzymes?
Gene cloning, DNA mapping, fingerprinting, SNP analysis.
Modification enzymes — examples?
Methylases, phosphatases, ligases, kinases.
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