The following table shows where different restriction endonucleases (restriction

Question

The following table shows where different restriction endonucleases (restriction enzymes) cleave DNA. The abbreviation R represents the purines (adenine and guanine). The pyrimidines (cytosine, thymine, and uracil) are abbreviated as Y. The abbreviation W represents adenine or thymine EnzymeTarget sequenceCleavage 5' GAATTC 3' 3' CTTAAG 5 5' GATATC 3' 3' CTATAG 5 5' GGCC 3' 3' CCGG 5. 5' AAGCTT 3 5' G AATTC 3' G 5' EcoRI EcORV Haelll Hindlll PpuMI 3' CTTAA 5' GAT ATC 3 3' CTA TAG 5 5' GG CC 3 3. ?? GG 5 5' A AGCTT 3' 3. TTCGAA 5 3. TTCGA A 5' 5' RGGWCCY 3 3. YCCWGGR 5 GWCCY 3' 5' RG ?' YCCWG GR 5 Which restriction endonuclease(s) would cleave a DNA molecule at the following sequences? a) 5' TCAGAATTCGGTGA 3" Haell EcoR Hindlill EcoRV Haelll EcORI Hindill continued below...

Explanation / Answer

Restriction endonucleases are naturally produced in bacteria that have been infected with bacteriophages to cut and kill the phage DNA.
Each Restriction Endonuclease recognise a specific base pair sequence on the length of the DNA called pallindromic recognition sequence where it cuts the the strands of the double helix of DNA.
It cuts both the strands at the same site between the same two bases.

(a) 5 'TCAGAATTCGGTGA 3' - It will be recognised and cut by EcoRI between G and A.

(b) 5' TCCAAGCTTGAATTC 3' - It will be recognised and cut by HindIII between A and A.
Note that this sequence also contains the recognition sequence of EcoRI at the end of the segment, but restriction endonucleases cannot cut the DNA from the ends.



As the Restriction endonuclease enzymes do not cut exactly at the middle of the sequence, they leave overhanging stretches which are called sticky ends. They facilitate the joining of two DNA fragments cut by the same Restriction Enzyme by forming hydrogen bonds.
If a Plasmid DNA and gene of interest are cut by PpuMI , the overhanging stretch in the 5 prime to 3 prime direction will be GWC. (refer table)

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