Cutting both strands of DNA harms the virus more than cutting one strand. Bacteria have evolved to 'disable' bacteria-targeting viruses (bacteriophages) using restriction enzymes that bind to these palindromic sequences. The last reason has been important in the struggle between viruses and bacteria. b) Consult Table 19.4 in your textbook to determine which restriction endonuclease. It is even possible that two enzymes work as a dimer to cut the palindromic sequence, further increasing efficiency. a) Identify the palindromic sequence in the duplex DNA molecule shown below. This means that the enzyme recognizes the sequence no matter from which side the enzyme approaches the DNA.Ī palindromic sequence also increases the chance that both strands of DNA are cut. A palindromic sequence is the same backwards and forwards on both sides (see image below). Luckily! because you don't want a 'pacman' that cuts DNA at random places.ĭNA is double stranded, so it has 'two sides' to which the enzyme can bind. It binds to the DNA only in one specific configuration. Recognizing a palindromic sequence allows them to cut both strands of DNA at the same site, because the strand will have the same sequence only in different directions at that site. Many do though, simply because it is more effective. For example, the recognition site for the restriction enzyme EcoRI is 5-GAATTC-3, which is palindromic. Not every restriction enzyme cuts palindromic sequences. They recognize short, usually palindromic, sequences of 48 bp and, in the presence of Mg 2+, cleave the DNA within or in close proximity to the recognition sequence. Restriction endonuclease Eco RI cuts the DNA strands a little away from the centre of the palindromic sequence, but between the same two bases on the two. The recognition sites of restriction enzymes are often palindromic, meaning that the DNA sequence reads the same in both forward and reverse directions. Restriction enzymes Authors: Hayat Ullah Government College University Faisalabad Abstract A restriction enzyme (or restriction endonuclease) is an enzyme that cuts DNA at or near. Enzymes such as restriction enzymes have to recognize a very specific sequence in order to carry out its task. A palindromic sequence is a nucleic acid sequence (DNA or RNA) that is the same whether read 5' (five-prime) to 3' (three prime) on one. More than 3000 type II restriction endonucleases have been discovered.
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