6. The following DNA fragment was sequenced by the Sanger method. The asterisk i
ID: 259891 • Letter: 6
Question
6. The following DNA fragment was sequenced by the Sanger method. The asterisk indicates a fluorescent label. 3'_ATTACGCAAGGACATTAGAC---5' A sample of the DNA was reacted with DNA polymerase and the following mixture nucleotides (in an appropriate buffer): dATP, dTTP, dCTP, dGTP, and ddTTP. The ddTTP was included at a relatively low concentration. The resulting DNA was separated by electrophoresis on an agarose gel and the band pattern shown in the box below. What is the sequence of the DNA in the band indicated by the arrow? a.*5'-Primer-ddT b. *5'-Primer-TAAddT c. *5'-Primer-TAATGCTddT d. *5'-Primer-TAATGCGddT e. *5'-Primer-TAATGCTTCCddT iriExplanation / Answer
During DNA elongtion, A binds with T and G binds with C or vice versa. As this mixure contain low amounts ddTTP, sometimes its replace dTTP, So, the chian terminates. As it pairs with A, where A bp is there there is a chance of termination of elongation strand.
During electrophoresis, the small fragements moves rapidly and occupaies the last part of the gel where as the large fragments moves slowly and occuapies the remaning gel positions accordingly.
So, here there is chance of chain termination at first A postion i.e. before TT, so it gives small fagment so, it moves rapidly occupaies the lowest part of the gel.
The second A is at fourth base i.e. before CG, so, here it terminates and occupaies the last but one band.
As the third A is at ninth position, the sequence will be primer TAATGCGddT, it occuapies the third band from lower side.
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