Question

Cell Biology Short Answer Question: Describe some typical features of a restriction enzyme recognition sequence and how blunt and staggered cuts are made.

Answer 1

Restriction endonuclease is an enzyme that cleaves DNA into fragments at specific recognition sites or some distance away within the molecule known as restriction sites. Cleavage can produce sticky ends (5? or 3? protruding ends) or blunt ends. Restriction enzymes cleave double-stranded DNA. There are four major classes of restriction endonucleases based on the types of sequences recognized, the nature of the cut made in the DNA, and the enzyme structure.

Type I: They have both restriction and methylation activities. There cleavage site a variable distance from recognition site and ATP is required for theire activity.

Type II?: There cleavage within or close to recognition sequence, It generates 5? phosphate and 3? hydroxyl termini at cleavage site. Mg2+ requirement for most for theire activity and ATP is not required.

Type III: There cleavage site a specific distance away from one of the recognition sequences and ATP is required for theire activity.

Type IV: Type IV enzymes recognize modified, typically methylated DNA. There cleavage site approximately 30 base pairs away from recognition site.

Blunt ends may result a straight cut, down through the DNA that results in a flat pair of bases on the ends of the DNA; however, there are no overhangs or unpaired bases.

Staggered cut may result a cutting of two DNA strands four base pairs from each other, creating a four-base 5' overhang in one molecule and a complementary 5' overhang in the other. These ends are called cohesive since they are easily joined back together by a ligase.