Unit-5

Glycolysis - is a metabolic pathway in which glucose in converted to pyruvate, energy released in this process is conserved in the form of ATP and NADH.

ED pathway - An alternative pathway to utilize glucose by which it is converted to pyruvic acid with the help of unique enzymes 6-phosphogluconate dehydratase and 2-keto-3-deoxyphosphogluconate aldolase.

ATP - Adenosine triphosphate is the energy currency of the cell system, used for various biosynthetic reaction of the cell.

Electron carriers - refers to different organic molecules that are capable of accepting one or more electrons from a donating molecule to the next carrier in the electron transport chain, during this process the energy level decreased. E.g. cytochromes and quinones

Fermentation - Defined as anaerobic type of metabolism in which organic compounds are oxidized in the absence or without the help of external electron acceptors. Thus the electron donor is an organic compound (glyceraldehyde) NADH2 is the electron carrier and the electron acceptor is also an organic compound (e.g.pyruvate or its derivatives).

Aerobic respiration - Form of respiration commonly operating in the living cells, in the process, O2 serves as terminal electron acceptor.

Anaerobic respiration - A kind of respiration that takes place only in members of bacteria, in this process oxidized form of inorganic compounds like NO3, SO4 acts as terminal electron acceptor

Electron transport system – it comprises of series of organic and protein complexes that freely diffuse or embedded in membrane that are involved in transfer of electron from electron donors to electron acceptors via redox (reduction-oxidation) reactions. This electron transfer is coupled with the extrusion of protons across the membrane leading to proton motive force formation outside the membrane that in turn helps in ATP synthesis.  

Substrate level phosphorylation - a process by which phosphorylated organic compounds (e.g. 1,3 diphospho glycerate and phosphoenol pyruvate) generated as an intermediate during substrate degradation (e.g. by glycolysis) is used for the synthesis of ATP at the substrate level instead of forming after operation of the electron transport chain.

Lactic acid fermentation - It is present in bacteria (lactic acid bacteria), protists (Chlorella and some water molds), and even in animal skeletal muscle. Lactic acid fermenters can be separated into two groups.  Homolactic fermenters - use the Embden-Meyerhof pathway and directly reduce almost all their pyruvate to lactate with the enzyme lactate dehydrogenase. Heterolactic fermenters form substantial amounts of products other than lactate; many also produce ethanol and CO2. Lactic acid bacteria are important to the food industry, where they are used to make a variety of fermented foods

Mixed Acid Fermentation: Many bacteria belonging to the member of Enterobacteriaceae can metabolize pyruvate to numerous products using several pathways simultaneously. One such complex fermentation is the mixed acid fermentation,  which results in the  excretion  of  ethanol  and  a  mixture  of  acids,  particularly acetic, lactic, succinic, and formic acids. Members of genera Escherichia, Salmonella and Proteus carry out mixed acid fermentation. If formic hydrogenolyase is present, formic acid will be degraded to H2 and CO2

Butanediol Fermentation: It is a complex fermentation characteristic of Enterobacter, Klebsiella, Serratia, Erwinia  and  some species of  Bacillus. The predominant pathway used during this fermentation process yields butanediol, a neutral pH product.  The use of either mixed acid fermentation or butanediol fermentation is important in differentiating members of the Enterobacteriaceae in the methyl red and Voges Proskauer reaction

Stickland fermentation - Some members of proteolytic Clostridia (C. sporogenes and C. botulinum) are capable of fermenting a mixture of amino acids. They carry out a reaction called Stickland Reaction, in which one amino acid is oxidized (alanine) and a second amino acid acts as the electron acceptor (glycine). Some ATP is formed by substrate-level phosphorylation, and the fermentation is quite useful for growing in anoxic, protein-rich environments.