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.
Key Characteristics of Prokaryotes vs Eukaryotes
| Feature | Prokaryote | Eukaryote |
|---|---|---|
| Nucleus | Absent (nucleoid region) | Present (membrane-bound) |
| Cell size | 1–10 µm | 10–100 µm |
| DNA structure | Circular, single chromosome | Linear, multiple chromosomes |
| Membrane-bound organelles | Absent | Present |
| Ribosomes | 70S | 80S (cytoplasmic) |
| Cell wall | Usually present (peptidoglycan in bacteria) | Varies by kingdom |
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Related Terms
Eukaryote
A eukaryote is an organism whose cells contain a membrane-bound nucleus housing the DNA, along with other membrane-enclosed organelles such as mitochondria, endoplasmic reticulum, and the Golgi apparatus. Eukaryotes include all plants, animals, fungi, and protists, and their cells are generally much larger and more structurally complex than prokaryotic cells. The compartmentalization of cellular functions within organelles allows eukaryotes to perform more specialized and regulated biochemical processes.
Cell Theory
Cell theory is the foundational scientific framework stating that all living organisms are composed of one or more cells, the cell is the basic structural and functional unit of life, and all cells arise from pre-existing cells. It was developed in the mid-19th century by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow. This theory unified biology by providing a common framework for understanding how all living systems are organized and how life perpetuates itself.
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.
From Greek "pro" meaning before and "karyon" meaning kernel or nut (referring to the nucleus). The term was coined by microbiologist Edouard Chatton in 1925 to distinguish organisms without a true nucleus from those with one.