Restriction endonucleases are the enzymes

Ans. b (They cleave the DNA at specific sequence) (Ref. Harper's Illustrated Biochemistry, 26lh/57, 397; Table 40-2)RESTRICTION ENDONUCLEASES# Restriction enzyme: An endodeoxynuclease that causes cleavage of both strands of DNA at highly specific sites dictated by the base sequence.# The detection of restriction fragment length polymorphisms (RFLPs) facilitates prenatal detection of hereditary disorders such as:- Sickle cell trait,- Beta thalassemia,- phenylketonuria, and- Huntington's disease.# Detection of RFLPs involves cleavage of double-stranded DNA by restriction endonucleases, which can detect subtle alterations in DNA that affect their recognized sites.Enzymes capable of degrading nucleic acids (nucleases) can be classified in several ways:# Those which exhibit specificity for deoxyribonucleic acid are referred to as deoxyribonucleases.# Those which specifically hydrolyze ribonucleic acids are ribonucleases.# Within both of these classes are enzymes capable of cleaving internal phosphodiester bonds to produce either 3'- hydroxyl and 5'-phosphoryl terminals or 5'-hydroxyl and 3'-phosphoryl terminals. These are referred to as endonucleases.# There exist classes of endonucleases that recognize specific sequences in DNA; the majority of these are the restriction endonucleases, which have in recent years become important tools in molecular genetics and medical sciences.# Some nucleases are capable of hydrolyzing a nucleotide only when it is present at a terminal of a molecule; these are referred to as exonucleases.- Exonucleases act in one direction (3-5 or 5-3) only. In bacteria, a 3-5 exonuclease is an integral part of the DNA replication machinery and there serves to edit--or proofread--the most recently added deoxynucleotide for base- pairing errors.Educational points:# Restriction enzymes cut DNA of any source into short pieces in a sequence-specific manner--in contrast to most other enzymatic, chemical, or physical methods, which break DNA randomly.# Restriction enzymes & DNA ligase are also used to prepare chimeric DNA molecules.