Prokaryotic cells lack
a. DNA.
b. a true nucleus.
c. a cell wall.
d. none of the above.
a
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When studying an ancient ecosystem's organisms, what was the advantage of looking for DNA samples in permafrost?
A. The freezing temperature preserves the DNA. B. The enzymes that make DNA are still active in the cells. C. Areas with permafrost are older than other parts of the world, allowing scientists to collect samples back 1.5 to 2 million years. D. It is easier to take solid core samples. E. Most plants and animals evolved in Siberia.
The two strands of DNA are held together by hydrogen bonds
Indicate whether the statement is true or false
Of the following, a receptor protein in a membrane that recognizes a chemical signal is most similar to
A) the active site of an allosteric enzyme that binds to a specific substrate. B) tRNA specifying which amino acids are in a polypeptide. C) a metabolic pathway operating within a specific organelle. D) an enzyme having an optimum pH and temperature for activity. E) an antibody in the immune system
Monotremes differ from the other mammals in their
A. laying of shelled eggs. B. carnivorous nature. C. fur. D. containing a pouch for young to live. E. lack of milk-producing glands.