Which of the following specifies a single amino acid in a polypeptide chain?
a. the three-base sequence of mrna
b. the complementarity of dna and rna
c. the aminoacyl-trna synthetase
d. the base sequence of the trna

What type of appendages do sponges cnidarians roundworms annelids mollusks arthropods echinoderms and vertebrate have? jointed, not jointed, absent  

What are the three different shapes, or structures, of carbon-based molecules

When is your breathing likely to speed up? a. when your white blood cells increase b. when your cells need more energy c. when your heart cells need more carbon dioxide d. when your blood cells have too much oxygen