Specific amino acids are attached to tRNA molecules by
A. hydrogen bonds.
B. aminoacyl-tRNA synthetases.
C. initiation factors.
D. anticodons.
E. deactivating enzymes.
Answer: B
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For many years, biologists felt that the highest level of classification of living organisms was the five kingdoms. Recently, some biologists have proposed that the hierarchical classification of organisms start with three domains, the Bacteria, the Archaea, and the Eucarya. Explain the reasoning behind this proposal and why the Bacteria and the Archaea should be in separate domains even though
their members are all prokaryotes. What will be an ideal response?
Among bryophytes, only the sporophytes of mosses and hornworts have stomata, whereas stomata are missing from liverwort sporophytes. If the common ancestor of all bryophytes had sporophytes that bore stomata, then which of these might account for their absence from liverwort sporophytes? If, in contrast to early mosses and hornworts, early liverwort sporophytes had
A) more-effective transport of glucose from gametophyte to sporophyte. B) increased robustness (i.e., thicker, more massive tissues). C) increased nutritional independence from the gametophyte. D) decreased need to broadcast spores long distances.
In order for macromolecules to form, smaller molecules must be concentrated. All of the following have been proposed as ways for concentrating organic molecules EXCEPT?
A. Organic molecules could have collected on the surface of clay particles. B. Organic molecules could have been concentrated when they were trapped in small basins and the water evaporated. C. Organic molecules could have made copies of themselves and this resulted in concentrations of molecules. D. Organic molecules could have been concentrated when water froze.
Microbes that use ammonium and nitrate as a source of electrons and CO2 as their sole source of carbon are said to be ________.
What will be an ideal response?