Which of the following statements concerning ribosomes are true?

• A. Several ribosomes are often attached to and translating the same mRNA.
• B. Ribosomes join amino acids to form a polypeptide.
• C. Ribosomes have a binding site for mRNA and three binding site for tRNA molecules.
• D. No protein synthesis within a cell would occur without ribosomes.
• E. All of the above statements are true.

Answer: (E)

Verified step by step guidance

1. Understand that ribosomes are the molecular machines in the cell responsible for protein synthesis. They read the sequence of the mRNA and translate it into a polypeptide chain.
2. Recognize that multiple ribosomes can attach to a single mRNA strand simultaneously, forming a structure known as a polysome or polyribosome. This allows for the efficient production of multiple copies of a protein from a single mRNA molecule.
3. Acknowledge that ribosomes facilitate the formation of peptide bonds between amino acids, thus joining them into a polypeptide chain. This is a fundamental role of ribosomes in protein synthesis.
4. Identify that ribosomes have specific binding sites: one for mRNA and three for tRNA molecules. These sites are crucial for the translation process, as they allow the ribosome to read the mRNA and bring in the appropriate tRNA carrying the correct amino acid.
5. Realize that ribosomes are essential for protein synthesis in the cell. Without ribosomes, the translation of mRNA into proteins would not occur, halting the production of proteins necessary for various cellular functions.