Question

in dna sequencing, how does the addition of dideoxynucleoside triphosphates (ddntps) terminate the synthesis of new dna? group of answer choices the ddntps lack a phosphate backbone, which prevents the addition of nucleotides. the ddntps have an additional hydroxyl group at the 2' end, which prevents the addition of nucleotides. the ddntps have a hydrogen instead of a hydroxyl group at the 3' end, which prevents the addition of nucleotides. the ddntps have a large substituent group that blocks the addition of nucleotides. ddntps do not terminate the synthesis of dna.

Answer 1

The addition of dideoxynucleoside triphosphates (ddNTPs) during DNA sequencing results in chain termination because ddNTPs lack a free 3' OH group needed for the formation of phosphodiester bonds with subsequent nucleotides.

Step-by-step explanation:

In the process of DNA sequencing, specifically through the dideoxy chain termination method, the addition of dideoxynucleoside triphosphates (ddNTPs) acts as a terminator for DNA synthesis. This occurs because ddNTPs lack a critical component for DNA polymerization: the free 3' OH group on the sugar molecule. DNA polymerases require this hydroxyl group to form the phosphodiester bond between the incoming nucleotide and the growing chain. Since ddNTPs have a hydrogen atom in the place where the hydroxyl group should be, no further nucleotides can be added once a ddNTP has been incorporated into the DNA strand.

When a ddNTP is included in a growing DNA sequence, it results in chain termination. This is because the missing 3' hydroxyl group prevents the addition of the next nucleotide, causing the synthesis to stop. This unique property of ddNTPs is utilized to create fragments of varying length in the method devised by Frederick Sanger, which are then analyzed to determine the DNA sequence.