Ribosomes and mitochondria are essential cellular components found in all eukaryotic cells.
Ribosomes
- Ribosomes are small organelles responsible for protein synthesis. They translate mRNA into proteins by assembling amino acids in the correct sequence
- They can be found free-floating in the cytoplasm or attached to the cytoplasmic side of the endoplasmic reticulum (forming rough ER)
- Ribosomes consist of two subunits, large and small, made of proteins and ribosomal RNA (rRNA)
- In eukaryotic cells, ribosomal RNA is synthesized in the nucleolus inside the nucleus, where ribosomes are also assembled before being transported to the cytoplasm
Mitochondria
- Mitochondria are double membrane-bound organelles that generate energy for the cell by converting organic molecules into ATP through cellular respiration
- They contain their own DNA and ribosomes (called mitoribosomes) which are attached to the inner mitochondrial membrane and synthesize some mitochondrial proteins encoded by mitochondrial DNA
- Most mitochondrial proteins, however, are encoded by nuclear DNA and synthesized by cytoplasmic ribosomes before being imported into mitochondria
- Mitoribosomes differ from cytoplasmic ribosomes in structure and composition but perform a similar role in protein synthesis within mitochondria
Summary of Locations
Component| Location in Cell
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Ribosomes| Free in cytoplasm or on rough ER membrane
Mitochondria| Cytoplasm, with mitoribosomes on inner membrane
Thus, ribosomes are found throughout the cytoplasm and on the rough ER, while mitochondria are distinct organelles with their own ribosomes embedded in their inner membranes
