Kornberg and his colleagues incubated soluble extracts of E. coli with a mixture of dATP, dTTP, dGTP, and dCTP, all labelled with 32P in the α-phosphate group. After a
time, the incubation mixture was treated with trichloroacetic acid, which precipitates the DNA but not the nucleotide precursors. The precipitate was collected, and the extent of precursor incorporation into DNA was determined from the amount of radioactivity present in the precipitate.
(a) If any one of the four nucleotide precursors were omitted from the incubation mixture, would radioactivity be found in the precipitate? Explain.
(b) Would 32P be incorporated into the DNA if only dTTP were labeled? Explain.
(c) Would radioactivity be found in the precipitate if 32P labelled the β or γ phosphate rather
than the α phosphate of the deoxyribonucleotides? Explain.
Kornberg and his colleagues incubated soluble extracts of E. coli with a mixture of dATP, dTTP, dGTP, and dCTP, all labelled with 32P in the α-phosphate group. After a
time, the incubation mixture was treated with trichloroacetic acid, which precipitates the DNA but not the nucleotide precursors. The precipitate was collected, and the extent of precursor incorporation into DNA was determined from the amount of radioactivity present in the precipitate.
(a) If any one of the four nucleotide precursors were omitted from the incubation mixture, would radioactivity be found in the precipitate? Explain.
(b) Would 32P be incorporated into the DNA if only dTTP were labeled? Explain.
(c) Would radioactivity be found in the precipitate if 32P labelled the β or γ phosphate rather
than the α phosphate of the deoxyribonucleotides? Explain.
Related textbook solutions
Related questions
Imagine Hershey/Chase had used an RNA virus (genome composed of RNA) instead of a DNA virus in their experiment. Would radioactivity still have been found in the pellet?
| A. | No, because only DNA can be labeled with radioactivity. |
| B. | No, because the RNA genome would not enter the bacteria upon infection. |
| C. No, because while DNA and RNA nucleotides are similar, they are not identical. |
| D. Yes, because DNA and RNA nucleotides are similar. |
| E. | Yes, because genome in any form (DNA, RNA, protein) would be labeled similarly. |
You accidentally add a mutant dNTP (which has an H instead of an OH connected to the 3â carbon) to a reaction where DNA is being replicated. Which of the following is true of this mutant dNTP?
| A. | It can be incorporated into DNA strand but cannot form a phosphodiester bond with an incoming wild type dNTP |
| B.It can be incorporated into a DNA strand but cannot base pair with a complementary nucleotide |
| C. It can be incorporated into a DNA strand and can form a phosphodiester bond with an incoming dNTP, but only if it is another mutant dNTP |
| D. | It cannot be incorporated into a DNA strand. |
3. Radioactive isotopes are commonly used as a means to measure incorporation into biological molecules. A researcher measured the incorporation of 32P-labeled ADP or 32-P labeled ATP into RNA. He added various nucleotide mixtures to an E. coli extract that catalyzed RNA synthesis. The table below lists the added components along with the observed radioactivity incorporated into the RNA (cpm = counts per minute).
| Reaction components | cpm incorporated |
| 1. ADP | 690 |
| 2. ADP, UDP, CDP, GDP | 1800 |
| 3. ATP | 790 |
| 4. ATP, UTP, CTP, GTP | 3920 |
3a. Based on your knowledge from this chapter and the data above, what enzyme is likely present in the E. coli extract?
3b. Why does reaction #4 has the greatest cpm value compared to other reactions?
4a. The genetic code was discovered to consist of 64 codons due to the fact that the 4 RNA nucleotides are read in triplets (43 = 64). Why would a 2 nucleotide codon system have been insufficient?
