- Eukaryotic cells have a true nucleus, bound by a double membrane. Prokaryotic cells have no nucleus. The purpose of the nucleus is to sequester the DNA-related functions of the big eukaryotic cell into a smaller chamber, for the purpose of increased efficiency. This function is unnecessary for the prokaryotic cell, because its much smaller size means that all materials within the cell are relatively close together. Of course, prokaryotic cells do have DNA and DNA functions. Biologists describe the central region of the cell as its “nucleoid” (-oid=similar or imitating), because it’s pretty much where the DNA is located. But note that the nucleoid is essentially an imaginary “structure.” There is no physical boundary enclosing the nucleoid.
- Eukaryotic DNA is linear; prokaryotic DNA is circular (it has no ends).
- Eukaryotic DNA is complexed with proteins called “histones,” and is organized into chromosomes; prokaryotic DNA is “naked,” meaning that it has no histones associated with it, and it is not formed into chromosomes. Though many are sloppy about it, the term “chromosome” does not technically apply to anything in a prokaryotic cell. A eukaryotic cell contains a number of chromosomes; a prokaryotic cell contains only one circular DNA molecule and a varied assortment of much smaller circlets of DNA called “plasmids.” The smaller, simpler prokaryotic cell requires far fewer genes to operate than the eukaryotic cell.
- Both cell types have many, many ribosomes, but the ribosomes of the eukaryotic cells are larger and more complex than those of the prokaryotic cell. Ribosomes are made out of a special class of RNA molecules (ribosomal RNA, or rRNA) and a specific collection of different proteins. A eukaryotic ribosome is composed of five kinds of rRNA and about eighty kinds of proteins. Prokaryotic ribosomes are composed of only three kinds of rRNA and about fifty kinds of protein.
- The cytoplasm of eukaryotic cells is filled with a large, complex collection of organelles, many of them enclosed in their own membranes; the prokaryotic cell contains no membrane-bound organelles which are independent of the plasma membrane. This is a very significant difference, and the source of the vast majority of the greater complexity of the eukaryotic cell. There is much more space within a eukaryotic cell than within a prokaryotic cell, and many of these structures, like the nucleus, increase the efficiency of functions by confining them within smaller spaces within the huge cell, or with communication and movement within the cell.
- Eukaryotic cells are the largest cells, while Prokaryotic cells are smaller than Eukaryotic cells. A eukartotic cell is about 10 times bigger than a prokaryotic cell.
- Eukaryotic cells either have a plasma membrane or a cell wall in addition to the plasma membrane; prokaryotic cells have a plasma membrane in addition to a bacterial cell wall
- Most primitive, earliest form of life
- Do not have a pre-defined nucleus
- Chromosomes are dispersed in the cytoplasm
- Contain no membrane-bound organelles
- Have circular chromosomes and lack histone proteins
- Most metabolically diverse
- Small – typically 0.2-2.0 micrometers in diameter
- Have a primitive cytosketetal structures or don’t have a cytoskeleton at all
- Smaller (70S) ribosomes
- Don’t undergo meiosis but reproduce sexually by the transfer of DNA fragments through conjugation
- More complex, evolved organsims
- Contain true nuclei in which chromosomes are compacted as chromatin
- Contain membrane-bound organelles
- Have linear DNA and contain histone proteins
- Larger – typically 10-100 micrometers in diameter
- Have a complex cytosketeton
- Larger (80S) ribosom
- Reproduce sexually with the use of meiosis