Trna synthetases play a key role in protein biosynthesis by catalyzing the specific aminoacylation of trna at their 3' ends, a two step reaction termed "charging" of trna. the tutorial depicts the binding of glutaminyl-trna synthetase and trna®ln. a uracil (u35) provides a key element for the recognition of trnagln by the synthetase enzyme. u35 of the trna is anchored in place by specific amino acids in the synthetase protein interacting ironically with the nearby backbone phosphates. a. amino acids with polar uncharged side chains b. amino acids with negatively charged side chains c. amino acids with positively charged side chains d. amino acids with hydrophobic side chains

Awater molecule is polar because there is an uneven distribution of these between the oxygen and hydrogen atoms.

Look at the images of different rocks. which rocks have a fine-grained texture? check all that apply. 1 2 3 4 5

Over the past 60 years, many amphibian species have experienced significant population declines and some species have become extinct. scientists suspected that local human activities such as the destruction of wetlands, regional pollution, and deforestation were the main reasons for these losses. however, research over the past 20 years reveals significant amphibian population declines in protected areas of the world, such as nature preserves and parks. these global declines suggest widespread problems including increased ultraviolet radiation, acid rain, and disease. in switzerland, for example, 14 of the 20 native amphibian species are threatened with extinction. chytridiomycosis is a fungal disease first identified in 1998 as a cause of massive amphibian deaths. in some severely impacted populations, a few individuals have survived, perhaps because of some natural resistance. if these resistant individuals continue to survive and prosper, new resistant populations might emerge. this would be an example of the founder effect artificial selection genetic drift natural selection sexual selection