Ribosomes are in most all cells, they are little dots inside the cell that are part of the protein-making machinery. Our bodies are made up of cells that are a different brand than the cells of bacteria. Our brand of cells have different sized ribosomes than bacteria. Our ribosomes are ignored by the aminoglycoside antibiotics. Oh, except for certain portions of some of our cells.
Mitochondria contain working parts that are very much like the ones in bacteria.
In a high enough dose, gent and all the other aminoglycoside antibiotics will disable some of our cells - probably by binding in mitochondria. The parts of our bodies most sensitive to aminoglycosides are the inner ears and the kidneys. Some of us have inherited a gene on our mitochondria that makes us especially vulnerable to the effects of these medicines. Some people are more susceptible. Those of us who have special gene sequences in the DNA of our mitochondria can become deaf with even a small dose of the aminoglycoside antibiotics.