Question

alexander adds only three of the four required nucleotides (datp, dgtp, dctp, but not dttp) to a dna sequencing reaction that uses dna polymerase. the template strand he is trying to sequence is 5-aatcggtacg-3. at what position will dna synthesis stop?
the first a in the template dna strand from the right
the first a in the template dna strand from the left
the first t in the template dna strand from the right
the first t in the template dna strand from the left
no synthesis will occur without all four nucleotides

Explanation:

DNA polymerase requires all four nucleotides (dATP, dGTP, dCTP, dTTP) for continuous synthesis. When a required nucleotide is missing, synthesis stops when the template strand requires that missing nucleotide. In DNA, adenine (A) on the template strand pairs with thymine (T) in the newly - synthesized strand. Since dTTP is missing, synthesis will stop when the template strand has an A and needs a T to be added to the new strand. Reading the template strand 5'-AATCGGTACG-3' from left to right, the first A is the point where synthesis will stop as there is no dTTP to pair with it.

Answer:

The first A in the template DNA strand from the left