Most of the dry weight of microorganisms is organic matter containing the elements carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. In addition, inorganic ions such as potassium, sodium, iron, magnesium, calcium, and chloride are required to facilitate enzymatic catalysis and to maintain chemical gradients across the cell membrane.

For the most part, the organic matter is in macromolecules formed by the introduction of anhydride bonds between building blocks. Synthesis of the anhydride bonds requires chemical energy, which is provided by the two phosphodiester bonds in adenosine triphosphate (ATP; see Chapter 6). Additional energy required to maintain a relatively constant cytoplasmic composition during growth in a range of extra cellular chemical environments is derived from the proton motive force. The proton motive force is the potential energy that can be derived by passage of a proton across a membrane. In eukaryotes, the membrane may be part of the mitochondrion or the chloroplast. In prokaryotes, the membrane is the cytoplasmic membrane of the cell.

The proton motive force is an electrochemical gradient with two components: a difference in pH (hydrogen ion con centration) and a difference in ionic charge. The charge on the outside of the bacterial membrane is more positive than the charge on the inside, and the difference in charge contributes to the free energy released when a proton enters the cytoplasm from outside the membrane. Metabolic processes that generate the proton motive force are discussed in Chapter 6. The free energy may be used to move the cell, to maintain ionic or molecular gradients across the membrane, to synthesize anhydride bonds in ATP, or for a combination of these purposes. Alternatively, cells given a source of ATP may use its anhydride bond energy to create the proton motive force that in turn may be used to move the cell and to maintain chemical gradients.

To grow, a bacterium requires all the elements in its organic matter as well as the full complement of ions required for energetics and catalysis. In addition, there must be a source of energy to establish the proton motive force and to allow macromolecular synthesis. Microorganisms vary widely in their nutritional demands and their sources of metabolic energy.

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مواضيع ذات صلة

Cultivation of Microorganisms : Sources of Metabolic Energy

Renewal of Epithelial Cells

Transport Across Epithelia

Covering or Lining Epithelia

Anticoagulants for Clinical use

The Rationale and Methodology for Hepcidin-Lowering Agents

Therapy of Iron Deficiency

Intestinal Iron Absorption

Liver Regulation of Systemic Iron Homeostasis and Iron Storage

Recycling of Erythrocyte Iron by Macrophages

Use of Iron For Erythropoiesis

Essential Features OF Red Blood Cell Homeostasis