Once the processed mRNA engages with the ribosomes, it is ready to synthesize the protein chain it encodes. The ribosome is a megadalton complex of many proteins and RNA. It consists of two principal sub-complexes, the small and large subunits, defined according to their molecular masses. The small subunit engages the mRNA, whereas the large subunit harbors the catalytic peptidyl transferase center. Protein synthesis is initiated upon binding of the aminoacylated-initiator tRNA to the start codon. The assembly of the initiating complex requires the assistance of many initiation factors in all three domains of life. Once correctly assembled, the elongation cycle starts with the participation of two major elongation factors until the ribosome encounters the termination codon. The termination codons are recognized by class I release factors, and the protein chains are terminated with assistance from class II release factors. Released and properly folded protein chains may be chemically modified to attain their desired activity. Numerous protein modifications have been identified, particularly in eukaryotes. They play a significant role in the regulation of biological functions. Protein degradation is an essential component of determining intracellular protein concentrations. Regulation of the degradation rate plays a crucial role in establishing the functional concentrations of proteins. In bacteria, a family of ATP-dependent proteases carries out the degradation. In eukaryotes, the modification of proteins by another small protein, ubiquitin, marks them for degradation. The proteasome, a large multi-subunit molecular machine, is the principal agent that carries out the degradation of ubiquitin-tagged proteins.