HiSET Science: Differences Between Prokaryotic and Eukaryotic Cells

Prokaryotes and Eukaryotes

Sizes and Metabolism
Cells of the domains of Bacteria and Archaea are prokaryotes. Bacteria cells and Archaea cells are much smaller than cells of eukaryotes. Prokaryote cells are usually only 1 to 2 micrometers in diameter, but eukaryotic cells are usually at least 10 times and possibly 100 times larger than prokaryotic cells. Eukaryotic cells are usually 10 to 100 micrometers in diameter. Most prokaryotes are unicellular organisms, although some prokaryotes live in colonies. Because of their large surface-area-to-volume ratios, prokaryotes have a very high metabolic rate. Eukaryotic cells are much larger than prokaryotic cells.

Due to their larger sizes, they have a much smaller surface-area-to-volume ratio and consequently have much lower metabolic rates.



Membrane-Bound Organelles
Prokaryotic cells are much simpler than eukaryotic cells. Prokaryote cells do not have a nucleus due to their small size and their DNA is located in the center of the cell in a region referred to as a nucleoid. Eukaryote cells have a nucleus bound by a double membrane. Eukaryotic cells typically have hundreds or thousands of additional membrane-bound organelles that are independent of the cell membrane. Prokaryotic cells do not have any membrane-bound organelles that are independent of the cell membrane. Once again, this is probably due to the much larger size of the eukaryotic cells.

The organelles of eukaryotes give them much higher levels of intracellular division than is possible in prokaryotic cells.

Cell Walls
Not all cells have cell walls, but most prokaryotes have cell walls. The cell walls of organisms from the domain Bacteria differ from the cell walls of the organisms from the domain Archaea. Some eukaryotes, such as some fungi, some algae, and plants, have cell walls that differ from the cell walls of the Bacteria and Archaea domains.

The main difference between the cell walls of different domains or kingdoms is the composition of the cell walls. For example, most bacteria have cell walls outside of the plasma membrane that contains the molecule peptidoglycan. Peptidoglycan is a large polymer of amino acids and sugars.

The peptidoglycan helps maintain the strength of the cell wall. Some of the Archaea cells have cell walls containing the molecule pseudopeptidoglycan, which differs in chemical structure from the peptidoglycan but basically provides the same strength to the cell wall.

Some fungi cell walls contain chitin. The cell walls of diatoms, a type of yellow algae, contain silica. Plant cell walls contain cellulose, and woody plants are further strengthened by lignin.

Some algae also contain lignin.
Animal cells do not have cell walls.

Chromosome Structure
Prokaryote cells have DNA arranged in a circular structure that should not be referred to as a chromosome. Due to the small size of a prokaryote cell, the DNA material is simply located near the center of the cell in a region called the nucleoid. A prokaryotic cell may also contain tiny rings of DNA called plasmids. Prokaryote cells lack histone proteins, and therefore the DNA is not actually packaged into chromosomes. Prokaryotes reproduce by binary fission, while eukaryotes reproduce by mitosis with the help of linear chromosomes and histone proteins. During mitosis, the chromatin is tightly wound on the histone proteins and packaged as a chromosome. The DNA in a eukaryotic cell is located in the membrane-bound nucleus.