Ribosomes have sites for two tRNA molecules, one called a peptidyl site and the other called an aminoacyl site. At this point the tRNA molecule in the peptidyl site is released and the ribosome scoots one step along the mRNA strand, thereby shifting the tRNA molecule in the aminoacyl site to the peptidyl site and opening a space for a new tRNA molecule. The cycle goes on with addition of the new tRNA molecule, formation of another peptide bond, release of a free tRNA molecule and another ribosomal shift. A copy of the universal genetic code is appended to the end of this column. Please note, for example, that the AGG in the mRNA strand shown above specifies the amino acid arginine.
Protein synthesis begins with transcription of a DNA strand within a cell nucleus.
JH receptor proteins are found within the cytosol of cells. JH forms a complex with its specific receptor, then the hormone-receptor complex moves into the nucleus. The natural foods of many insects include substantial amounts of carbohydrates, or sugars, either in the form of simple sugars or as polymers. Following absorption across midgut epithelium, sugars are removed from circulating hemolymph into fat bodies. The polymerization of simple sugars into glycogen is called glycogen synthesis, and is carried out enzymatically by glycogen synthetase.