TIU Faculty of Science Medical Analysis Department Microbial
TIU - Faculty of Science Medical Analysis Department Microbial physiology Heshu J. Ahmed/Assist. Lecturer _______________________ Microbial metabolic pathways – Stage /1 st Semester Heshu. jalal@tiu. edu. iq https: //tiu. edu. iq/ 2020 - 2021
The Entner–Doudoroff Pathway • The Entner–Doudoroff pathway is an alternate series of reactions that catabolize glucose to pyruvate. • The Entner–Doudoroff pathway describes an alternate series of reactions that catabolize glucose to pyruvate using a set of enzymes different from those used in either glycolysis or the pentose phosphate pathway.
• Glycolysis =glucose C 6 H 12 O 6 into pyruvate. • The free energy released in this process is used to form the high-energy compounds ATP and NADH. • Most bacteria use glycolysis and the pentose phosphate pathway.
• Distinct features of the Entner–Doudoroff pathway are that it occurs only in prokaryotes. • and it uses 6 -phosphogluconate dehydratase and KDPG to create pyruvate from glucose. • The Entner–Doudoroff pathway also has a net yield of 1 ATP for every glucose molecule processed, as well as 1 NADH and 1 NADPH.
• There a few bacteria that substitute classic glycolysis with the Entner-Doudoroff pathway. They may lack enzymes essential for glycolysis. • Most organisms that use the pathway are aerobes due to the low ATP yield per glucose such as Pseudomonas, a genus of Gram-negative bacteria, and Azotobacter, a genus of Gramnegative bacteria.
Aerobic Hydrocarbon Oxidation • hydrocarbon: A compound consisting only of carbon and hydrogen atoms. • biosurfactant: Surface-active substances synthesized by living cells. • bioremediation: The use of biological organisms, usually microorganisms, to remove contaminants, especially from polluted water.
• Microbes can use many different carbon sources for energy. The best known and perhaps most common example is glucose. • Microbes can utilize hydrocarbons via a stepwise oxidation of a hydrocarbon produces : water and, successively, an alcohol, an aldehyde and then a peroxide.
• This is of special interest as many of the environment pollutants released by human industry are often hydrocarbon based. • Understanding how microbes digest hydrocarbons has started the field of microbial biodegradation, a type of bioremediation. • The goal of this is to find ways of using microbes to degrade hydrocarbon spills or waste into less dangerous byproducts such as alcohol.
• Several microorganisms are known to synthesize surface-active agents; most of them are bacteria and yeasts. • When grown on hydrocarbon substrate as the carbon source, these microorganisms synthesize a wide range of chemicals with surface activity, such as glycolipid, phospholipid, and others. • These chemicals are synthesized to emulsify the hydrocarbon substrate and facilitate its transport into the cells.
• biosurfactant-producing microorganisms may play an important role in the accelerated bioremediation of hydrocarboncontaminated sites. • these compounds can also be used in enhanced oil recovery and may be considered for other potential applications in environmental protection.
The Pentose Phosphate Pathway • The pentose phosphate pathway (PPP) converts glucose-6 -phosphate into NADPH and pentoses (5 -carbon sugars). • glycolysis: The cellular degradation of the simple sugar glucose to yield pyruvic acid and ATP as an energy source. • NADPH: Nicotinamide adenine dinucleotide phosphate (NADP) carrying electrons and bonded with a hydrogen (H) ion; the reduced form of NADP+.
• There are two distinct phases in the pathway: the oxidative phase and the non-oxidative phase. • In the oxidative phase, two molecules of NADP+ are reduced to NADPH, utilizing the energy from the conversion of glucose-6 phosphate into ribulose-5 -phosphate. These NADPH molecules can then be used as an energy source in elsewhere in the cell. • The non-oxidative phase generates 5 -carbon sugars, which can be used in the synthesis of nucleotides, nucleic acids, and amino acids. • The pentose phosphate pathway is an alternative to glycolysis.
Glucose 6 -phosphate + 2 NADP+ + H 2 O → ribulose-5 -phosphate + 2 NADPH + 2 H
• The PPP is one of the three main ways the body creates molecules with reducing power, accounting for approximately 60% of NADPH production in humans.
Organic Acid Metabolism acetyl Co. A: Acetyl coenzyme A or acetyl-Co. A is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production.
• Some microbes are capable of utilizing organic acids such as fatty acids, amino acids, or straight-chain unsaturated acids (e. g. , lactate) as a sole source of energy. • Many bacteria are capable of utilizing fatty acids as sole energy and carbon sources through the cyclic β-oxidation pathway, which ultimately yields acetyl-Co. A.
The most commonly metabolized organic acids are the carboxylic acids, which are organic acids containing at least one carboxyl (-COOH) group. Many types of carboxylic acids can be metabolized by microbes, including: • Fatty acids (carboxylic acids with long acyl tails) • Amino acids (the building blocks of proteins) • Straight-chained, saturated acids (e. g. , formate, acetate, and palmitate)
FATTY ACID METABOLISM Many bacteria are capable of utilizing fatty acids of various tail lengths as sole energy and carbon sources. This process requires the β-oxidation pathway, a cyclic process that catalyzes the sequential shortening of fatty acid acyl chains to the final product, acetyl. Co. A. The step-by-step process occurs as follows: 1. Fatty acid chains are converted to enoyl-Co. A (catalyzed by acyl-Co. A dehydrogenase). 2. Enoyl-Co. A is converted to 3 -hydroxyacyl-Co. A (catalyzed by enoyl-Co. A hydratase). 3. 3 -hydroxyacyl-Co. A is converted to 3 -ketoacyl-Co. A. 4. 3 -ketoacyl-Co. A is thiolated to yield one molecule of acetyl-Co. A and a derivative of the original input fatty acid that is now shorter by two carbons.
β-oxidation of fatty acids: Free fatty acids are broken down to acetyl-Co. A by dedicated enzymes in the β -oxidation pathway.
Connecting Proteins to Glucose Metabolism • Amino acids must be deaminated before entering any of the pathways of glucose catabolism: • the amino group is converted to ammonia, which is used by the liver in the synthesis of urea.
• Deaminated amino acids can be converted into pyruvate, acetyl Co. A, or some components of the citric acid cycle to enter the pathways of glucose catabolism. • Several amino acids can enter the glucose catabolism pathways at multiple locations.
• Proteins are hydrolyzed by a variety of enzymes in cells. • Most of the time, the amino acids are recycled into the synthesis of new proteins or are used as precursors in the synthesis of other important biological molecules, such as hormones, nucleotides, or neurotransmitters. • However, if there are excess amino acids, or if the body is in a state of starvation, some amino acids will be shunted into the pathways of glucose catabolism.
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