As with DNA replication, the free nucleotides in the transcription are initially nucleoside triphosphates. The breaking away of the two phosphates under the influence of the RNA polymerase provides the free energy for the construction of the covalent phosphodiester bonds between nucleotides.
In the diagrams the nucleoside triphosphates are just drawn as nucleotides. The main phases of translation are imaged although remember that prokaryotes do not have intron regions of the eukaryotes. The inclusion of promoter regions and terminator regions is a simplification of prokaryote gene expression.
In 1965 Francoise Jacob, Jacques Monod and Andre Lwoff received the Nobel Prize for their discoveries of the mechanism which controls prokaryotic gene expression. The implications for our understanding of gene expression and developmental biology are wide ranging and even today they are still opening up new fields of understanding in biology. If every you thought a scientist is a boring individual wearing white coats tucked away in a laboratory, then you should read the works of Jacob and Monod. These war time freedom fighters in the French Resistance not only produced beautiful theories of gene expression but also crafted elegant literature prized as much for its philosophy as its biology.
J. Monod, Chance and Necessity (New York: Alfred A. Knopf, 1971)