Final answer:
The structure formed by an mRNA molecule and multiple simultaneously translating ribosomes is known as a polyribosome or polysome, facilitating efficient protein synthesis.
Step-by-step explanation:
The combination of a messenger RNA (mRNA) and many bound ribosomes in the process of translation is called a polyribosome (or polysome). A polyribosome is a cellular structure that features multiple ribosomes simultaneously translating a single mRNA molecule. This efficient system allows for multiple copies of a protein to be synthesized at the same time from a single mRNA transcript. During translation in the cytoplasm, each ribosome moves along the mRNA in the 5' to 3' direction, creating a polypeptide chain in accordance with the genetic code contained within the mRNA sequence.