There are _____ codons to code for the 20 possible amino acids
A. 20
B. 30
C. 64
D. 61
D
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Fungi
A. take in food by phagocytosis. B. generate ATP and reducing equivalents by photosynthesis. C. absorb nutrients from the environment. D. All of these choices are correct.
Which began first?
A. Multicellular life in the ocean B. Animals colonizing the land C. Multicellular life in fresh water D. Plants colonizing the land
The scissors in the figure represent
a. restriction enzymes. b. reverse transcriptases. c. DNA polymerases. d. RNA polymerases. e. DNA ligases
For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labeling the nitrogen atoms would provide a stronger signal than labeling the phosphates. Why won't this experiment work?
a) Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive b) Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long c) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins d) There is no radioactive isotope of nitrogen