Metabolism
Metabolism is the chemical reactions which keep us alive. It happens in the cells of living organisms.
The chemical reactions are catalyzed by enzymes. Metabolism allows organisms to grow, reproduce, maintain their structures, and respond to their environments. The word ‘metabolism’ can also refer to digestion and the transport of substances into and between different cells.
Metabolism is usually divided into two categories:
- Catabolism breaks down organic matter and harvests energy by way of cellular respiration.
- Anabolism uses energy to build molecules such as proteins and nucleic acids.
The chemical reactions of metabolism are organized into metabolic pathways, or cycles, like the Krebs cycle. One chemical is transformed through a series of steps into another chemical by a series of enzymes.
The metabolic system of an organism decides which substances it finds nutritious and which poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals.[1] The speed of metabolism, called the metabolic rate, influences how much food an organism will need, and how it is able to get that food.
A striking feature of metabolism is the similarity of the basic metabolic pathways and components between even vastly different species.[2] For example, the set of carboxylic acids that are best known as the intermediates in the citric acid cycle are present in all known organisms, being found in species as diverse as the unicellular bacterium Escherichia coli and huge multicellular organisms like elephants.[3] These striking similarities in metabolic pathways are likely due to their early appearance in the evolution of life, and kept because of their efficiency.[4][5]
Metabolism Media
Simplified view of cellular metabolism
Structure of a triacylglycerol lipid
Glucose can exist in both a straight-chain and ring form.
Structure of adenosine triphosphate (ATP), a central intermediate in energy metabolism
The structure of iron-containing hemoglobin. The protein subunits are in red and blue, and the iron-containing heme groups in green. From PDB 1GZX.
A simplified outline of the catabolism of proteins, carbohydrates and fats
Carbon Catabolism pathway map for free energy including carbohydrate and lipid sources of energy
Mechanism of ATP synthase. ATP is shown in red, ADP and phosphate in pink and the rotating stalk subunit in black.
Plant cells (bounded by purple walls) filled with chloroplasts (green), which are the site of photosynthesis
Simplified version of the steroid synthesis pathway with the intermediates isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and squalene shown. Some intermediates are omitted for clarity.
Related pages
References
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Pace N.R. (2001). "The universal nature of biochemistry". Proc. Natl. Acad. Sci. U.S.A. 98 (3): 805–8. Bibcode:2001PNAS...98..805P. doi:10.1073/pnas.98.3.805. PMC 33372. PMID 11158550.
- ↑ Smith E. & Morowitz H. (2004). "Universality in intermediary metabolism". Proc Natl Acad Sci USA. 101 (36): 13168–73. Bibcode:2004PNAS..10113168S. doi:10.1073/pnas.0404922101. PMC 516543. PMID 15340153.
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).
- ↑ Lua error in Module:Citation/CS1/Identifiers at line 630: attempt to index field 'known_free_doi_registrants_t' (a nil value).