24-6 DNA Sequencing Methods for sequencing immense DNA chains 1.First step in sequencing Cleave the DNA chain at known points to produce smaller pieces,done through the use of restriction endonucleases More than 3800 restriction enzymes are known About 375 restriction enzymes are commercially available Each different restriction enzyme cleaves a DNA molecule at a point in the chain where a specific base sequence occurs The restriction enzyme Alul cleaves between G and C in the four-base sequence AG-CT (5'-AGCT-(3)sequence is that same as its complement(3)- TCGA-(5)when both are read in the same 53'direction Methods for sequencing immense DNA chains 1. First step in sequencing ▪ Cleave the DNA chain at known points to produce smaller pieces, done through the use of restriction endonucleases ▪ More than 3800 restriction enzymes are known ▪ About 375 restriction enzymes are commercially available ▪ Each different restriction enzyme cleaves a DNA molecule at a point in the chain where a specific base sequence occurs ▪ The restriction enzyme AluI cleaves between G and C in the four-base sequence AG-CT ▪ (5′-AGCT-(3′) sequence is that same as its complement (3′)- TCGA-(5′) when both are read in the same 5′→3′ direction 24-6 DNA Sequencing