Q. What is the cellular structure to which mRNA molecules bind to start the protein synthesis?

To make proteins mRNA molecules essentially associate to ribosomes. Ribosomes have two sites for the binding of two neighboring mRNA codons and where anticodons of tRNA bind by hydrogen bond. Thus ribosomes are the structure responsible for the exposure and positioning of mRNA codons to be translated. In ribosomes the peptide bond between two amino acids brought by tRNA molecules also occurs. The peptide bond happens when tRNAs carrying amino acids are bound to exposed mRNA codons.