Skip to main content

Respiration, Cellular

Respiration, Cellular

Cellular respiration is the process by which a cell produces adenosine triphosphate (ATP), carbon dioxide, and water from oxygen and organic (carbon-based) fuel. It is a catabolic pathway (a pathway that breaks down compounds into simpler components) that involves the release of stored energy. Respiration involves a variety of chemical reactions that occur in a step-wise fashion, in several coordinated groups. These reaction groupings are known as glycolysis, the Krebs cycle, and electron transport.

In eukaryotes, the mitochondria is the primary organelle that contains the enzymes that drive cellular respiration. Nearly all eukaryotic cells contain some mitochondria. While there may be as few as one mitochondria in a cell, often there are hundreds or thousands. The number typically depends on the metabolic activity of the cell. The mitochondria is enclosed in a two membrane envelope in which a variety of proteins are embedded. Inside these membranes is the mitochondrial matrix which contains some of the enzymes that function in cellular respiration. Other enzymes, including the one that makes ATP, are attached to the inner membrane. This configuration provides an efficient way for cellular respiration to occur.

Although the mitochondria contains most of the enzymes related to cellular respiration, the process actually begins in the cytosol. This reaction, known as glycolysis, involves the breakdown of glucose into two molecules of a three carbon sugar called pyruvate. During this process, two molecules of ATP are consumed while four molecules of ATP are produced, resulting in a net gain of two ATP molecules. While this energy is beneficial to the cell, it pales in comparison to the amount produced by the later stages of cellular respiration.

After glycolysis, the pyruvate is transported across the mitochondrial membranes into the matrix. Here, it goes through a series of reactions called the Krebs cycle (also known as the citric acid cycle). First it is converted to acetyl CoA. It is then slowly oxidized into carbon dioxide and water. Two molecules of ATP are also formed during this stage.

The final step in cellular respiration is the electron transport reactions. These reactions complete the oxidation of glucose and generate the greatest amount of energy. During this stage, each of the storage molecules transfers electrons to a series of coenzymes which then drive the production of ATP molecules. The actual production of ATP is the result of an enzyme called ATP synthase. This enzyme produces ATP from ADP by a process called oxidative phosphorylation. This phase of cellular respiration results in about 34 molecules of ATP.

In addition to glucose, many other compounds are used by the cell as a source of fuel. These include proteins, carbohydrates, and fats. All of these complex molecules can be broken down to simpler ones which can then enter glycolysis or the Krebs cycle at various points. For example, starch is hydrolyzed in the digestive tract producing a molecule that can be broken down by glycolysis. Similarly, glycogen can be hydro-lyzed. Proteins are used as fuel, but only after they are reduced to their constituent amino acids and their amino groups are removed. Fats are the highest energy containing molecules. They are reduced to either glycerol or acetyl CoA before entering the cellular respiration reactions.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Respiration, Cellular." The Gale Encyclopedia of Science. . Encyclopedia.com. 25 Sep. 2018 <http://www.encyclopedia.com>.

"Respiration, Cellular." The Gale Encyclopedia of Science. . Encyclopedia.com. (September 25, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/respiration-cellular-0

"Respiration, Cellular." The Gale Encyclopedia of Science. . Retrieved September 25, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/respiration-cellular-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.