anaerobic respiration


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an·aer·o·bic res·pi·ra·tion

a form of respiration in which molecular oxygen is not consumed, for example, nitrate respiration, sulfate respiration.

an·aer·o·bic res·pi·ra·tion

(an'ār-ō'bik res'pir-ā'shŭn)
A form of respiration in which molecular oxygen is not consumed (e.g., nitrate respiration, sulfate respiration).
Anaerobic respirationclick for a larger image
Fig. 35 Anaerobic respiration . Energy release in anaerobic and aerobic respiration.
Anaerobic respirationclick for a larger image
Fig. 34 Anaerobic respiration . Breakdown of pyruvic acid to ethanol.

anaerobic respiration

a type of cell respiration that takes place in ANAEROBES, and in which energy is released from glucose and other foods without the presence of oxygen. The reactions fall into two stages:

Stage 1: GLYCOLYSIS, in which glucose is converted to two molecules of pyruvic acid (pyruvate) in the general cell cytoplasm. The same reactions occur as in AEROBIC RESPIRATION, but in anaerobes the absence of oxygen prevents the two resulting molecules of reduced NAD from being oxidized via the ELECTRON TRANSPORT SYSTEM (ETS) in the MITOCHONDRIA. Instead, ATP is produced from ADP by SUBSTRATE-LEVEL PHOSPHORYLATION. Thus the net output of ATP in anaerobic respiration is 2 molecules (4 minus 2 used in the initial phosphorylation).

Stage 2: once pyruvate has been produced, two alternative pathways can occur. In plants and many microorganisms the pyruvate is broken down to ethanol via ethanal (acetaldehyde) in a process called ALCOHOLIC FERMENTATION, which requires hydrogen from NADH (see Fig. 34 ). In animals the pyruvate is changed via a single step into LACTIC ACID, a process called lactic-acid fermentation, which again requires hydrogen from NADH.

The role of NADH in both fermentations should be noted. Since the amount of NAD present in the cell is limited, glycolysis would quickly come to a halt if anaerobic respiration stopped at pyruvate. By going on to ethanol or lactic acid, NAD is freed in the fermentations to return to glycolysis and thus allow glucose CATABOLISM to continue. The yield of ATP in anaerobic respiration is poor because, firstly, the ETS cannot be used without oxygen, and, secondly, the end products still contain large amounts of energy. As a result, the free energy released and stored is only a fraction of the amount in the complete oxidation of glucose, as is shown in Fig. 35.

References in periodicals archive ?
Low values of ethanol under low [O.sub.2] atmospheres indicated less anaerobic respiration rate, a reduction of off-flavours and better consistency.
Using one of the search engines on the Internet, such as Google, Yahoo!, Ask.com, or MSN Live Search, find more information by searching for these words or phrases: law of thermodynamics, energy conversion, anaerobic respiration, aerobic respiration, oxidation reduction, photosynthesis, pigments, light reactions, ATP, ADP, Calvin cycle, Krebs cycle, stomata, glycolysis, fermentation, glucose, protein, lipids, and amino acids.
Survival would rely on normoxic conditions remaining stable long enough for them to be capable of anaerobic respiration or rebuild energetic reserves (de Zwaan 1977).
Microbial fuel ceils are a current research area that harvests electricity from bacteria capable of anaerobic respiration (Holmes et al., 2004; Liu et al., 2004; Logan et al., 2005).
At longer distances, however, the horse begins to run out of air and must employ anaerobic respiration, this time using energy that is delivered to its muscles at a slower rate.
Denitrification, an anaerobic respiration process in which nitrate is reduced to [N.sub.2] gas by bacteria (1, 2, 3), is an important nitrogen sink in estuarine systems.
The acute respiratory alkalosis may be accompanied by metabolic acidosis if the hypoxia is severe enough to cause the buildup of lactic acid resulting from anaerobic respiration.
Instead, cells get fuel from an oxygen-free reaction called anaerobic respiration.
Like aerobic respiration, anaerobic respiration also breaks down glucose, but instead of carbon dioxide and water the reaction produces a chemical called pyruvic acid.