Multiple Choice
The final step in a Sanger DNA sequencing reaction is to run the DNA fragments on a gel. What purpose does this serve?
17. Biotechnology
Dideoxy Sequencing
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Dideoxy sequencing is also known as chain termination sequencing because:
A
The dideoxy nucleotide prevents further synthesis of DNA due to the lack of a free 5' carbon.
B
The dideoxy nucleotide prevents further synthesis of DNA due to the lack of a free 3' OH.
C
The dideoxy nucleotide prevents further synthesis of DNA due to the lack of a nitrogen-containing base.
D
Chain termination is the same as sequencing by synthesis.
E
None of the above are correct.
Verified step by step guidance1
Understand the basic principle of dideoxy sequencing, also known as Sanger sequencing, which involves the incorporation of dideoxynucleotides (ddNTPs) to terminate DNA strand elongation.
Recognize that a dideoxynucleotide lacks a 3' hydroxyl (OH) group, which is essential for forming a phosphodiester bond with the next nucleotide, thus preventing further DNA synthesis.
Identify the role of the 3' OH group in DNA synthesis: it acts as a nucleophile that attacks the 5' phosphate of the incoming nucleotide, allowing the chain to elongate.
Evaluate the given options: The correct reason for chain termination in dideoxy sequencing is the absence of the 3' OH group in ddNTPs, not the 5' carbon or a nitrogen-containing base.
Conclude that the correct statement is: 'The dideoxy nucleotide prevents further synthesis of DNA due to the lack of a free 3' OH.' This is the fundamental reason for chain termination in Sanger sequencing.
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Dideoxy Sequencing practice set
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