There are sixty-one mRNA codons that specify an amino acid, but only forty-five tRNAs. This is best explained by the fact that _____
A) some tRNAs have anticodons that recognize four or more different codons
B) the rules for base pairing between the third base of a codon and tRNA are flexible
C) many codons are never used, so the tRNAs that recognize them are dispensable
D) the DNA codes for all sixty-one tRNAs, but some are then destroyed
E) competitive exclusion forces some tRNAs to be destroyed by nucleases
Answer: B
You might also like to view...
The movement of air along parabronchi is most similar to the movement of _____
A) air in the lungs of other amniotes B) food/waste in a gastrovascular cavity C) a mouse passing through the digestive system of a snake D) the frog tongue during feeding E) air in lungs of terrestrial amphibians
A population in biology refers to a group of organisms that
A. are different species. B. are genetically related. C. are the same species. D. live in the same space. E. cannot interbreed.
Among the natural defenses present in tears is the protein lactoferrin. As you can infer from its name, it is also present in milk and other body secretions, and its function involves binding iron ions. The presence of lactoferrin in tears is protective against bacterial infection because
A. pathogens with magnetosomes will be segregated from the eye tissue and swept away by the tears. B. free iron serves as an immune signal to recruit T cells to the eye. C. in the presence of lysozyme, as found in tears, the proteins form a protective barrier on the lens. D. all pathogens must acquire iron from their environment and lactoferrin ensures that the iron concentration is low.
Identify and briefly discuss two ecological roles filled by bacteria. What will be an ideal response?