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Principles of Biology

Eukaryotes and prokaryotes

Fields of Study

Biochemical Engineering; Cell and Tissue Engineering; Drug Testing; Environmental Microbiology; Histology; Industrial Fermentation; Pathology; Pharmacology; Sewage Engineering; Toxicology; Virology; Zymurgy and Zymology

Summary

Energy captured during the formation of glucose during photosynthesis is released during the processes involved in respiration in the human body. The glycolytic pathway breaks down the glucose molecule into carbon dioxide and water, and uses the energy released by the chemical changes to drive the processes of metabolism. When oxygen is not available, pyruvic acid from glucose is broken down to lactic acid rather than degraded further. Buildup of lactic acid in overworked muscles causes a burning sensation. Prokaryotic cells derive metabolic energy from glucose anaerobically via the lactic acid fermentation process, and are unable to grow and produce adenosine triphosphate (ATP) in the presence of oxygen. Eukaryotic cells require oxygen for growth and the production of ATP.

Principal Terms

  • eukaryotic cell: a complex cell on which all life more complex than a bacterium or yeast is based, characterized by a nucleus containing the cell’s DNA and a number of specialized organelles, supplied with energy by mitochondria, which individually resemble the more primitive prokaryotic cell. See also prokaryotic cell.

  • fermentation: a biological process for breaking down complex organic compounds into simpler compounds. One of the most familiar in human history is the conversion by yeast of sugar to carbon dioxide, alcohol, and water. Fermentation also occurs in cells, including animal muscle cells, breaking down glucose to produce lactic acid, lactate, carbon dioxide, and water, as well as adenosine triphosphate, a source of energy. It is less efficient than cellular respiration but occurs when muscles are short of oxygen. Many anaerobic bacteria ferment sugars: Lactobacillus ferment milk to produce yogurt. Fermentation also produces lactic acid in a variety of foods, such as sauerkraut and sourdough bread.

  • microbe: any microscopic form of life, also called a microorganism, particularly bacteria, protozoa, fungi, or virus. Most commonly, this term refers to pathogenic microscopic life—those that cause infection, disease, decay, sepsis, or gangrene. However, biologists are identifying an increasing number of microbes that are beneficial, even essential to life, including a variety of those found in the human intestine.

  • mitochondria: a type of organelle within eukaryotic cells, where oxygen and nutrients are converted into adenosine triphosphate, the molecule that stores chemical energy for the cell. This process, called aerobic respiration, is possible only in the presence of oxygen. Mitochondria are rod-shaped, have their own DNA, and reproduce independently within the cell, resembling some primitive prokaryotic cells. This suggests that prokaryotic cells were absorbed within the cell walls of evolving eukaryotic cells in a symbiotic relationship. Mitochondria enable cells to produce adenosine triphosphate fifteen times more efficiently than is possible by anaerobic respiration.

  • nucleus (cell): an organelle within each living eukaryotic cell that acts as a control center, storing genes on chromosomes, producing messenger RNA molecules (which transfer code for essential proteins from genes in the chromosomes), producing ribosomes, and organizing replication of DNA, including complete copies for cell division.

  • prokaryotic cell: the earliest and most primitive type of cell, probably the first life form on Earth, lacking a cell nucleus. Most bacteria are prokaryotic. Most one-celled animals, such as paramecium, and simple plants such as algae have the more complex eukaryotic cell.

Basic Principles of Cell Theory

Living organisms of all kinds are characterized as an assembly of individual cells that exist in a cooperative or symbiotic relationship with each other. The individual assemblages of cells of different types. The various unique assemblies of cells to form individual organisms produces the immense variety of members of the plant and animal kingdoms. The essential feature of the structures is the cell, all of which are defined as either a prokaryotic cell or a eukaryotic cell. The fundamental difference between the two types of cell is very distinct. A eukaryotic cell has a distinct internal structure, including a nucleus (cell), while a prokaryotic cell does not. The nucleus of a eukaryotic cell contains the DNA that defines the identity of the organism, and exists as a separate structure within the actual cell. Accordingly, all cells in the human body are eukaryotic cells. A prokaryotic cell lacks this internal definition, and in a way can be thought of as a nucleus without a surrounding cell. Eukaryotic cells contain a number of other internal structures that add to their complexity. This includes various membrane structures, organelles and fibers. A list of the major components of a eukaryotic cell includes the cell nucleus, the mitochondria, rough and smooth forms of a structure called the endoplasmic reticulum, and vacuoles. All eukaryotic cells also contain peroxisomes, while plant cells contain glyoxisomes and chloroplasts that are absent from animal cells. Mitochondria carry out the energy-producing functions of the cells. Various biochemical transformations take place at the endoplasmic reticulum. Vacuoles serve as storage sites for nutrients and wastes. All protist, fungus, animal and plant cells are eukaryotic cells. Prokaryotic cells, on the other hand, are exclusively one-celled microbes or bacteria.

Prokaryotes

The prokaryotes include all bacteria, and are generally divided into the classes of eubacteria and archaebacteria. The eubacteria are the photosynthetically active blue-green algae, or cyanobacteria. The archaebacteria are typically found in “unusual” environments. For example, the archaebacteria known as methanogens, for their production of methane as a byproduct, are found in swamps where the water and soil are free of oxygen, and in the digestive tracts of bovines such as cows. The methane is produced as a byproduct of anaerobic fermentation by methanogenic bacteria. Another branch of archaebacteria is the halophiles, bacteria that require high salt concentrations in their environment. Still another is known as the thermoacidophiles, requiring hot acidic sulfur springs in order to survive. Almost all prokaryotic cells, all of which are microbes, are “obligate anaerobes,” and do not grow or function in the presence of oxygen. Prokaryotes are simple in structure, being essentially just a fluid-filled sack formed by a semipermeable phospholipid bilayer membrane. This basic structure allows the passage of gases such as methane and carbon dioxide across the membrane, but utilizes a number of different protein structures embedded in the membrane to transport sugars, amino acids and ions across the membrane.

Eubacteria

The prokaryote class of eubacteria have a slightly different structure, and are classed as either Gram-negative or Gram-positive, according to their response to the Gram staining method. Gram-positive eubacteria have a cell wall layer and an adjacent plasma membrane, and give a positive response to the Gram staining method. Gram-negative eubacteria have an additional structural layer between the cell wall itself and the internal plasma membrane. This additional layer provides a higher degree of structural rigidity, and apparently prevents the Gram stain from penetrating. They therefore give a negative response to the Gram staining method.

Richard M. Renneboog MSc

See also: Cell Organelles.

Further Reading

1 

Favor, Lesli J. Eukaryotic and Prokaryotic Cell Structures. Understanding Cells With and Without a Nucleus New York, NY: Rosen Publishing Group, 2005.

2 

Campbell, Mary K. and Farrell, Shawn O. Biochemistry 8th ed., Stamford, CT: Cengage Learning, 2015.

3 

Hall, Brian K. and Hallgrimsson, Benedikt Strickberger’s Evolution 4th ed., Sudbury, MA: Jones and Bartlett, 2008.

4 

Weeks, Benjamin S. Alcamo’s Microbes and Society 3rd ed., Sudbury, MA: Jones and Bartlett Learning, 2012.

5 

Clark, David P. Molecular Biology Burlington, MA: Elsevier, 2010.

Fascinating Facts About Prokaryotes and Eukaryotes

  • The methane produced by methanogenic bacteria in cattle has been responsible for untoward pyrotechnic events in poorly ventilated cattle and dairy barns, while the methane produced by methanogenic bacteria in swamps is believed to be responsible for the phenomenon of glowing ‘swamp gas’.

  • Many of the colored deposits seen in geysers and acidic hot springs are due to the presence of thermophilic bacteria.

  • It is now believed that most digestion in the human gut is carried out by the trillions of bacteria that inhabit the human gut. The bacteria break down food materials to their molecular components, often altering their molecular structure in the process, and these nutrients are then transported across the membranes of the digestive tract and into the blood stream for use by the many different cells in the body.

  • Fermentation processes that utilize prokaryotic bacteria have become industrially important for the synthesis of many different pharmaceutical candidate compounds, as a source of plastics and biofuels. Bacterial pools are also used to clean up heavy metal toxic wastes from mining operations and for the treatment of sewage.

Citation Types

Type
Format
MLA 9th
"Eukaryotes And Prokaryotes." Principles of Biology, edited by A. Crawford Christina, Salem Press, 2017. Salem Online, online.salempress.com/articleDetails.do?articleName=POB_0058.
APA 7th
Eukaryotes and prokaryotes. Principles of Biology, In A. C. Christina (Ed.), Salem Press, 2017. Salem Online, online.salempress.com/articleDetails.do?articleName=POB_0058.
CMOS 17th
"Eukaryotes And Prokaryotes." Principles of Biology, Edited by A. Crawford Christina. Salem Press, 2017. Salem Online, online.salempress.com/articleDetails.do?articleName=POB_0058.