Ribosome
Ribosomes are small, dense ribonucleoprotein complexes found in all living cells that carry out protein synthesis (translation) by decoding messenger RNA (mRNA) sequences into polypeptide chains. Each ribosome consists of two subunits — a large subunit and a small subunit — composed of ribosomal RNA (rRNA) and proteins, with prokaryotic ribosomes being 70S and eukaryotic cytoplasmic ribosomes being 80S. Ribosomes can be found free in the cytoplasm, where they synthesize cytosolic proteins, or bound to the rough endoplasmic reticulum, where they produce proteins destined for secretion or membrane insertion.
Comparison of Prokaryotic and Eukaryotic Ribosomes
| Feature | Prokaryotic Ribosome | Eukaryotic Ribosome |
|---|---|---|
| Sedimentation coefficient | 70S | 80S |
| Large subunit | 50S (23S rRNA + 5S rRNA + ~31 proteins) | 60S (28S, 5.8S, 5S rRNA + ~49 proteins) |
| Small subunit | 30S (16S rRNA + ~21 proteins) | 40S (18S rRNA + ~33 proteins) |
| Location | Cytoplasm | Cytoplasm and rough ER surface |
| Sensitivity to antibiotics | Yes (e.g., streptomycin, erythromycin) | No (used in antibiotic treatments) |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Cell Nucleus
The cell nucleus is a large, membrane-bound organelle found in eukaryotic cells that serves as the control center of the cell, housing the cell's genetic material (DNA) organized into chromosomes. It is surrounded by a double membrane called the nuclear envelope, which contains nuclear pores that regulate the transport of molecules between the nucleus and the cytoplasm. The nucleus directs cell activities by controlling gene expression, coordinating DNA replication during cell division, and producing ribosomal RNA in a specialized subregion called the nucleolus.
Endoplasmic Reticulum
The endoplasmic reticulum (ER) is an extensive network of interconnected membrane-bound tubules and flattened sacs (cisternae) that extends throughout the cytoplasm of eukaryotic cells and is continuous with the outer nuclear envelope. It exists in two forms: rough ER (RER), which is studded with ribosomes and specializes in the synthesis, folding, and quality control of proteins destined for secretion or membrane insertion; and smooth ER (SER), which lacks ribosomes and is involved in lipid synthesis, calcium storage, and detoxification of drugs and toxins. The ER works closely with the Golgi apparatus to process and sort proteins and lipids to their correct cellular destinations.
Prokaryote
A prokaryote is a unicellular organism whose cell lacks a membrane-bound nucleus and other membrane-enclosed organelles, with genetic material floating freely in the cytoplasm as a nucleoid region. Prokaryotes include bacteria and archaea and represent the oldest and most abundant forms of life on Earth, having existed for approximately 3.5 billion years. They play essential roles in nutrient cycling, decomposition, nitrogen fixation, and many biotechnology applications.
From ribonucleic acid (RNA) combined with Greek "soma" meaning body. The term was coined by scientist Richard B. Roberts in 1958 to name the RNA-rich particles involved in protein synthesis that had been observed by George Palade in the early 1950s using electron microscopy.