31. Why does incorporation of a dideoxynucleotide into a growing DNA polymer ter

Question

31. Why does incorporation of a dideoxynucleotide into a growing DNA polymer terminate strand synthesis?

a. There is no longer a free 5’ phosphate to which to add the next nucleotide.

b. There is no longer a free 3’ hydroxyl to which to add the next nucleotide.

c. There is no longer a free 3’ phosphate to which to add the next nucleotide.

d. There is no longer a free 5’ hydroxyl to which to add the next nucleotide.

2. The output from an automated sequencing reaction shows a series of fluorescent peaks. When considering the data output, why are some peaks larger than others?

a. Chain termination occurred more frequently at the base corresponding to a large peak, producing a relatively larger fluorescent signal.

b. The primer had multiple bases fluorescently labeled for products corresponding to the larger peaks.

c. More bases were fluorescently labeled in the DNA strands corresponding to the larger peaks.

d. Some fluorescent colors are brighter than others.

3. What allows chain termination to occur at each base of the template during an automated sequencing reaction?

a. the presence of a relatively low concentration of ddNTPs

b. the presence of a relatively low concentration of dNTPs

c. the presence of a relatively high concentration of ddNTPs

d. the presence of a relatively high concentration of dNTPs

4. In automated fluorescent sequencing, what would happen if the fluorescently labeled ddATP was inadvertently omitted from the reaction?

a. DNA polymerase does not function without equal concentrations of the four nucleotides

b there would be gaps in the sequence where thymines were present in the template DNA strand

c. the sequence would end where the first thymine was encountered on the template DNA strand

d. the sequence would end where the first adenine should be incorporated

Explanation / Answer

1.
b. There is no longer a free 3’ hydroxyl to which to add the next nucleotide.
The lack of the 3'-hydroxyl group meaning that after being added by a Deoxyribonucleic polymerase to a growing nucleotide chain, further nucleotides can not be added as because no phosphodiester bond can be created based on the fact that Deoxyribonucleic triphosphates allow synthesis of Deoxyribonucleic chain to occur through a condensation reaction into the 5' of the present nucleotide with the 3' OH group of the antecedent nucleotide.

2.
a. Chain termination occurred more frequently at the base corresponding to a large peak, producing a relatively larger fluorescent signal.

Because variation in the efficiency of termination or chain elongation by the polymerase since because of sequence context inefficient or effects incorporation of the dideoxy(ddNTPs) nucleotide, from degraded or impure reagents, or from the laboratory protocol errors.

3.
c. the presence of a relatively high concentration of ddNTPs
Lower the concentrations of ddNTP, chain termination will be less likely, & we will get larger products
Higher the concentration of the Dideoxynucleotides in the reaction, the smaller the products

4.
c. the sequence would end where the first thymine was encountered on the template DNA strand

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.