Advanced Placement (AP) Biology Practice Exam

Which of the following best describes the function of ribosomes?

1. Packaging proteins for secretion

2. Synthesis of lipids

3. Synthesis of RNA

4. Protein synthesis

The correct answer is: Protein synthesis

Ribosomes play a crucial role in the cell's ability to produce proteins, which are essential for numerous biological functions, including structural support, enzyme activity, and regulatory mechanisms. The primary function of ribosomes is to translate messenger RNA (mRNA) into polypeptide chains, which then fold into functional proteins. This process involves reading the sequence of codons on the mRNA, each of which corresponds to specific amino acids, and facilitating the formation of peptide bonds between those amino acids to build the protein. Ribosomes can be found either floating freely in the cytosol or attached to the endoplasmic reticulum (forming rough ER). Regardless of their location, their fundamental task remains the same: protein synthesis. This is a critical process for cellular function and organismal health, hence making the answer focused on protein synthesis the most accurate choice.