In an experiment similar to that performed by Shatkin and colleagues, a student synthesized mRNAs such that 32P-GTP was incorporated; 7-meG labeled with 3H was used to cap the mRNA
A fraction of the sample was run on a gel and confirmedthat radiolabeled capped transcripts had indeed been produced. The remainder of mRNA was incubated with wheat germ cell extract to allow binding to ribosomes. The sample was deposited at the top of a sucrose density gradient and spun in a centrifuge. Surprisingly, neither label comigrated with the ribosome fraction; the ribosomes did migrate as expected. What is the most likely reason for this result?
A. The ribosomes did not incorporate the 3H label.
B. The sucrose gradient was not made correctly.
C. The wheat germ was contaminated with guanylyltransferase.
D. The wheat germ was contaminated with RNase
E. The centrifuge did not spin at the correct speed.
D
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Cell division is regulated by:
A. growth factor signals. B. signals that indicate a sufficient size of the cell. C. signals that indicate that DNA has been replicated. D. signals about the nutritional status of the cell. E. All of these choices are correct.
Which of the following was observed by Erwin Chargaff?
A. Base composition of DNA does not vary from one species to another. B. The DNA isolated from different tissues of the same species all have the same base composition. C. Base composition changes as the organism ages. D. In all species, the number of adenines equals the number of guanines. E. In all species, A + T = G + C.
In club fungi, each club-shaped cell initially ____
a. is a spore b. is a zygote c. contains a single nucleus d. is dikaryotic e. undergoes mitosis to produce spores
The rapid leaf movements resulting from a response to touch (thigmotropism) primarily involve _____
A) potassium channels B) nervous tissue C) aquaporins D) stress proteins