Eukaryotes contain a variety of membrane-bound organelles, including mitochondria for aerobic respiration, chloroplasts for photosynthesis, and the Golgi apparatus for protein modification. These structures allow for high metabolic efficiency through localized chemical environments.
Prokaryotes lack all membrane-bound organelles; their metabolic processes occur either in the cytoplasm or across the cell surface membrane. They do, however, possess ribosomes for protein synthesis.
Ribosome size is a key distinction: prokaryotes have smaller ribosomes, while eukaryotes have larger ribosomes in their cytoplasm. Interestingly, eukaryotic mitochondria and chloroplasts contain ribosomes, supporting the theory of their bacterial ancestry.
Most prokaryotes possess a rigid cell wall made of peptidoglycan (also called murein). This is a complex polymer of sugars and amino acids that provides structural support and prevents the cell from bursting due to osmotic pressure.
Eukaryotic cell walls are only found in certain groups and are chemically distinct from those of prokaryotes. Plant cell walls are primarily composed of cellulose, while fungal cell walls are made of chitin.
Animal cells are notable for completely lacking a cell wall, relying instead on an internal cytoskeleton and the extracellular matrix for structural integrity.
Prokaryotes reproduce asexually through a process called binary fission. This involves the replication of the circular DNA followed by the physical splitting of the cell into two identical daughter cells, without the use of a spindle apparatus.
Eukaryotic cells divide via mitosis or meiosis, complex processes that involve the condensation of chromosomes and the use of a microtubule spindle to ensure accurate segregation of genetic material.
While binary fission is rapid and efficient for simple organisms, the eukaryotic cell cycle includes multiple checkpoints and regulatory phases to manage the division of their more complex internal structures.
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Average Size | Up to | |
| DNA Structure | Circular, naked in cytoplasm | Linear, with histones in nucleus |
| Organelles | None membrane-bound | Mitochondria, Golgi, ER, etc. |
| Ribosomes | (cytoplasm) | |
| Cell Wall | Peptidoglycan (Murein) | Cellulose (plants) or Chitin (fungi) |
| Cell Division | Binary Fission | Mitosis or Meiosis |
Identification: In electron micrographs, the presence of any internal double membrane (like the nuclear envelope or mitochondrial cristae) immediately identifies a cell as eukaryotic. If the cell appears empty except for small dots (ribosomes) and a tangled mass (DNA), it is prokaryotic.
Ribosome Trap: Remember that while eukaryotes have ribosomes, they also contain ribosomes inside their mitochondria and chloroplasts. Do not let this confuse you if a question specifies the location of the ribosomes.
Cell Wall Materials: Always specify the material. Simply saying "has a cell wall" is often insufficient; you must distinguish between the peptidoglycan of bacteria and the cellulose of plants to earn full marks in comparison questions.
