Substance and energy change

This article deals generally with metabolic forms of living things. For the production of energy in living beings, see energy metabolism . For the special case of muscle cells, see energy supply .

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Living beings can be assigned to different metabolic forms based on their own metabolism of substances and energy . On the one hand , all organisms need energy in order to maintain their life processes. In principle, there are various ways of generating energy. On the other hand, they need a source of carbon from which to build their biomass . There are also a number of different options for carbon extraction. In the case of microorganisms, there are many forms of such material and energy changes. The division into various pure and mixed forms is therefore of great importance and diversity, especially in microbiology . In contrast to this, most multicellular cells behave in a uniform metabolic physiological manner .

Overview

The different metabolic forms are classified according to three criteria: energy source, electron donation and carbon source. In order to denote them conceptually as peculiarities of the metabolism, the word ending “-trophie” is added to their names (from ancient Greek τροφή trophe , German “nutrition” ).

Overview

Energy source	light	Photo-			-trophy
	Redox reaction	Chemo-
Electron donation (at) or	inorganic substance		Litho-
	organic matter		Organo-
Carbon source	inorganic substance			Automobile-
	organic matter			Hetero-

Two or three characteristics can be combined in one name. Green plants are phototrophic and lithotrophic and autotrophic. Accordingly, they are referred to as "photolithoautotrophic". Animals and fungi are chemotrophic and organotrophic and heterotrophic. They are therefore considered to be "chemoorganoheterotroph".

The presented overview of metabolism and energy changes does not take into account whether an organism uses oxygen ( aerobics / anaerobics ). It still does not pay attention to how its thermogenesis happens ( endothermia / ectothermia ). In addition, biology knows other meanings for the word trophy .

Type of energy source: phototrophy, chemotrophy

An energy source is required to synthesize the energy carrier and short-term energy store adenosine triphosphate (ATP) by phosphorylation from adenosine diphosphate (ADP) and phosphate . The splitting of the ATP into ADP and phosphate then provides the energy for energy-consuming processes, especially for building biomass.

• Phototrophy : The source of energy is light . Typical phototrophic organisms are green plants.
  • Radiotrophic fungi can also gain energy from ionizing radiation . This form of energy generation has only been described for a few mushrooms with the pigment melanin . The mechanism of the reaction is unclear.
• Chemotrophy : The energy source is exergonic metabolism, usually redox reactions . All non- phototrophic organisms are chemotrophic. The chemotrophic forms of metabolism include respiration and fermentation .

Type of electron donation: lithotrophy, organotrophy

An electron source ( electron donor , reducing agent ) is required to carry out reductions in the course of the building metabolism. Nicotinamide adenine dinucleotide (NAD) ⁺ and nicotinamide adenine dinucleotide phosphate (NADP ⁺ ) function as electron carriers between the electron source and the substances involved in building metabolism . For this purpose, both molecules are reduced to NADH or NADPH. The subsequent oxidation of the NAD (P) H (back to NAD (P) ⁺ ) later supplies the electrons for building biomass.

• Lithotrophy : The electrons come from the oxidation of inorganic substances . Typical lithotrophic organisms are nitrifying bacteria .
  • Hydrotrophy : The electrons come from the oxidation of the inorganic substance water . So the hydrophy is just a certain form of the lithotrophy. However, because of its importance, it is highlighted separately. Typical hydrotrophic organisms are green plants.
• Organotropy : The electrons come from the oxidation of organic substances . Typical organotrophic organisms are animals.

Type of carbon source: autotrophy, heterotrophy

A source of carbon is needed to build biomass.

• Autotrophy : The carbon comes exclusively from carbon dioxide (CO ₂ ) or from hydrogen carbonate ions (HCO ₃ ^- ) . Typical autotrophic organisms are green plants.
• Heterotrophy : The carbon comes at least partially from organic compounds. Typical heterotrophic organisms are animals.

Organisms that are capable of both autotrophy and heterotrophy practice mixotrophy .

literature

• MT Madigan, JM Martinko: Brock Microbiology . Munich 2006, ISBN 3-8273-7187-2 .
• U. Sonnewald: Physiology. In: Strasburger textbook of botany. Heidelberg 2008, ISBN 978-3-8274-1455-7 .

Individual evidence

1. ↑ MT Madigan, JM Martinko: Brock microbiology . Munich 2006, ISBN 3-8273-7187-2 , pp. 604, 621.
2. ↑ E. Dadachova, RA Bryan, X. Huang, T. Moadel, AD Schweitzer, P. Aisen, JD Nosanchuk, A. Casadevall: Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized fungi. In: PLoS ONE. 2 (2007), p. E457. doi: 10.1371 / journal.pone.0000457 (full text)
3. ^ U. Sonnewald: Physiology. In: Strasburger textbook of botany. Heidelberg 2008, ISBN 978-3-8274-1455-7 , pp. 224-225.