Prokaryotic cell structure

Information from: http://www.cod.edu/people/faculty/fancher/prokeuk.htm

· "Karyose" comes from a Greek word which means "kernel," as in a kernel of grain. In biology, we use this word root 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."

· Therefore, prokaryotic cells have no nuclei, while eukaryotic cells do have true nuclei. This is far from the only difference between these two cell types, however.

Here's a simple visual comparison between a prokaryotic cell and a eukaryotic cell, “assembled” by a composite of views taken with light and electron microscopes:

The reality: Bacillus anthracis, stained with Giemsa stain, 1000x magnification, under a light microscope	The reality: Cheek cells stained with methylene blue, 400x magnification, under a light microscope

Similarities:

· They perform most of the same kinds of functions, and in the same ways (cell division, energy transformation, metabolism;

· Both are enclosed by plasma membranes, filled with cytoplasm, and loaded with small structures called ribosomes;

· Genetic code is the identical.

Differences

· Prokaryotic cells lack membrane-bound organelles;

· Enzyme pathways are different;

· Ribosomal structure is slightly different

· Prokaryotic cells tend to be smaller

· 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

· Prokaryotic cells possess “mesosomes”, shallow invaginations of the cell membrane which allow for positioning of enzymes and pigments.

Eukaryotic cells may have evolved by endosymbiosis involving 2 or more prokaryotic cells

· Both chloroplasts and mitochondria possess their own DNA, which codes for proteins unique to those respective organelles;

· Endosymbiosis suggests that a larger prokaryote ingested a smaller one (e.g. cyanobacteria), which could photosynthesize, and the smaller one lost vestigial DNA and structures and became the current chloroplast.