Final answer:
Most damaged proteins in a cell are broken down in the cytosol, not the Golgi apparatus, endoplasmic reticulum, or peroxisomes. The process involves a proteasome that degrades proteins marked with ubiquitin.
Step-by-step explanation:
In a cell, most damaged proteins are broken down in the cytosol by a complex called the proteasome. The proteasome is a sophisticated protein complex that degrades unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. The proteins tagged for degradation by the addition of a small protein called ubiquitin are recognized and processed by the proteasome, resulting in smaller peptides and amino acids that can be recycled by the cell. While the Golgi apparatus is involved in modifying and packaging proteins, it is not the primary site for the breakdown of damaged proteins.
To address the reference information provided: Cells with a high concentration of smooth endoplasmic reticulum (smooth ER) include those that make steroid hormones. The RNA components of ribosomes are synthesized in the nucleolus. Congenital disorders of glycosylation that affect glycoproteins usually involve the Golgi apparatus. Additionally, plant cell components that carry out the function of lysosomes are called vacuoles.