Metabolism consists of two sets of biochemical pathways called anabolism and catabolism. Anabolism builds complex molecules from simpler ones, while catabolism breaks larger molecules into smaller ones. Anabolism and catabolism go hand-in-hand, as each makes the source material for the other. Anabolism requires energy, while catabolism produces energy that fuels anabolism.
Differences Between Anabolism and Catabolism
There are several key differences between anabolism and catabolism:
|Builds complex molecules from simpler ones||Breaks complex molecules into smaller ones that are easier to absorb or excrete|
|Requires energy (endothermic)||Releases energy (exothermic); Often spontaneous|
|Converts kinetic energy into potential energy (e.g., weightlifting)||Converts potential energy into kinetic energy (e.g., aerobic exercise)|
|Uses hormones including adrenalin, glucagon, and cortisol||Uses insulin and anabolic steroids|
|Builds proteins, nucleic acids, glycogen, triglycerides||Breaks larger molecules into amino acids, glucose, fatty acids, carbon dioxide, water|
|Used for growth, repair, and energy storage||Performs several activities, including thermoregulation, energy supply, digestion|
Anabolism and Catabolism Examples
Anabolic processes make proteins, repair damage, and grow tissues. Here are examples of anabolic processes and their chemical reactions:
- Glycerol reacts with fatty acids to make lipids:
CH2OHCH(OH)CH2OH + C17H35COOH → CH2OHCH(OH)CH2OOCC17H35
- Simple sugars combine to form disaccharides and water:
C6H12O6 + C6H12O6 → C12H22O11 + H2O
- Amino acids join together to form dipeptides, which act as the building blocks of proteins:
NH2CHRCOOH + NH2CHRCOOH → NH2CHRCONHCHRCOOH + H2O
- Carbon dioxide and water react to form glucose and oxygen in photosynthesis:
6CO2 + 6H2O → C6H12O6 + 6O2
- Weightlifting and other anaerobic exercises are anabolic processes. This type of exercise promotes muscle repair and growth.
Catabolism breaks down complex molecules into simpler ones that are more useful to the cell. Sometimes, it breaks down molecules so they are easier to dispose of as waste in the form of carbon dioxide, ammonia, acetic acid, lactic acid, and urea. Catabolism generates heat and may produce chemical energy, often in the form of ATP. The energy may drive anabolism or help regular body temperature. Here are some examples of catabolic processes and their reactions:
- During cellular respiration, glucose and oxygen react to yield carbon dioxide and water
C6H12O6 + 6O2 → 6CO2 + 6H2O
- In cells, hydroxide peroxide decomposes into water and oxygen:
2H2O2 → 2H2O + O2
- Aerobic exercise, such as a cardio workout is a catabolic process. Fat (or muscle) releases heat and carbon dioxide as it is broken down.
- Proteins break into amino acids
- Lipids break into fatty acids
- Nucleic acids break into nucleotides
- Polysaccharides break into disaccharides and monosaccharides
Anabolism and Catabolism Hormones
Hormones play an important role in metabolism. Some hormones are associated with anabolism or catabolism:
Anabolic hormones include insulin and the anabolic steroids:
- Human growth hormone
Catabolic hormones include:
- Orexin (Hypocretin)
An amphibolic pathway is a metabolic pathway that can be either anabolic or catabolic, depending on the availability of energy. These pathways either produce energy or consume it to make products, depending on the needs of the cell. Examples of amphibolic pathways are the citric acid cycle and glyoxylate cycle.
- Alberts, B.; Johnson, A.; Julian, L.; Raff, M.; Roberts, K.; Walter, P. (2002). Molecular Biology of the Cell (5th ed.). CRC Press.
- Berg, J. M.; Tymoczko, J. L.; Stryer, L.; Gatto, G. J. (2012). Biochemistry (7th ed.). New York: W.H. Freeman. ISBN 9781429229364.
- de Bolster, M. W. G. (1997). “Glossary of Terms Used in Bioinorganic Chemistry”. International Union of Pure and Applied Chemistry.
- Nicholls D. G. and Ferguson S. J. (2002) Bioenergetics (3rd Ed.). Academic Press. ISBN 0-12-518121-3.
- Ramsey K. M., Marcheva B., Kohsaka A., Bass J. (2007). “The clockwork of metabolism”. Annu. Rev. Nutr. 27: 219–40. doi:10.1146/annurev.nutr.27.061406.093546