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Prokaryotic and Eukaryotic Cells


Cells in our world come in two basic types, prokaryotic and eukaryotic. "Karyose" comes from a Greek word, which means "kernel," as in a kernel of grain. In biology, we use this root word to refer to the nucleus of a cell. "Pro" means "before," and "eu" means "true," or "good." So "Prokaryotic" means "before a nucleus," and "eukaryotic" means "possessing a true nucleus." This is a big hint about one of the differences between these two cell types. Prokaryotic cells have no nuclei, while eukaryotic cells do have true nuclei. However this is not the only difference between these two cell types. 

Here's a simple visual comparison between a prokaryotic cell and a eukaryotic cell. This particular eukaryotic cell happens to be an animal cell, but the cells of plants, fungi and protists are also eukaryotic.

Prokaryotic Cell


Animal cell

Despite their apparent differences, these two cell types have a lot in common. They perform most of the same kinds of functions, and in the same ways. Both are enclosed by plasma membranes, filled with cytoplasm, and loaded with small structures called ribosomes. Both have DNA, which carries the archived instructions for operating the cell. And the similarities go far beyond the visible - physiologically they are very similar in many ways. For example, the DNAs in the two cell types are very much the same kind of DNA, and the genetic code for a prokaryotic cell is exactly the same genetic code as used in eukaryotic cells. 

Some things which seem to be different aren't. For example, the prokaryotic cell has a cell wall, and this animal cell does not. However, many kinds of eukaryotic cells do have cell walls. 

Despite all these similarities, the differences are also clear. It's pretty obvious from these two little pictures that there are two general categories of difference between these two cell types: size and complexity. Eukaryotic cells are much larger and much more complex than prokaryotic cells. These two observations are not unrelated to each other. 

If we take a closer look at the comparison of these cells, we see the following differences: 
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 ribosomes, but the ribosomes of the eukaryotic cells are larger and more complex than those of the prokaryotic cell. Ribosomes are made 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.




Compare prokaryotic and eukaryotic cells.



1. Both have DNA as their genetic material.
2. Both are membrane bound.
3. Both have ribosomes.
4. Both have similar basic metabolism.
5. Both are amazingly diverse in forms.

Difference between Prokaryotic and Eukaryotic Cells 


Prokaryotic Cell

Eukaryotic Cell

Lack of organized nucleus. The presence of the genetic material in the form of nucleoid.

Nucleus well organized.

Nuclear membrane absent.

Nuclear membrane present.

DNA not complexed with histones.

DNA complexed with histones to constitute chromatin.

DNA in a circular form; not packed into chromosomes.

Linear DNA, packed into well defined chromosomes.

Membrane-bound organelles absent.

Membrane-bound organelles like ER, golgi, lysosomes, etc., present.

Mitochondria absent.

Mitochondria present.

Chloroplast absent. Photosynthetic lamellae may be present in photosynthetic bacteria.

Chloroplast present in plant cells.

Ribosomes only of 70S type.

Ribosomes of 80S (in cytoplasm) and 70S (in organelles) types in plant cells; and 80S and 55S types in animal cells.

Cell wall made up of murein.

Cell wall absent in animal cells; in plant cells it is made up of cellulose, hemicellulose lignin.

Flagella simple, made up of flagellin and 9+2 organisation is absent.

Flagella specialized and show 9+2 organisation.

Cytoplasmic streaming not observed. 

Cytoplasmic streaming is observed.

Microtubules absent.

Microtubules-forming cytoskeleton present.

Different kinds of pili present.

Pili absent.


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