Microbial Metabolism: Catabolism and Anabolism

Chapter 8: Microbial Metabolism

• Microbial Metabolism covers Metabolism, Energy, Pathways, and Biosynthesis.

Metabolism

• Catabolism, anabolism, and the role of enzymes are key components in microbial metabolism.
• Metabolism involves controlled biochemical reactions within a microbe, leading to the reproduction of the organism.

Catabolism and Anabolism

• Catabolism and anabolism are the two major classes of metabolic reactions.
• Catabolic pathways involve the breakdown of larger molecules into smaller products and are exergonic
• Anabolic pathways synthesize large molecules from the products of catabolism and are endergonic.
• Catabolism uses enzymes to break down complex organic molecules to extract energy and form simpler end-products.
• Anabolism uses enzymes to use energy from catabolism to synthesize macromolecules and cell structures from simpler products.

Enzymes

• Enzymes have functions, structures, enzyme-substrate interaction, utilize cofactors, perform actions and undergo regulation
• Enzymes serve as catalysts for chemical reactions and function by lowering the energy of activation.

Enzyme Structure

• Simple enzymes consist of protein alone
• Conjugated enzymes consist of both protein and nonprotein components.
• 3-D features enable specificity through the active site, also named the catalytic site.
• Conjugated enzymes necessitates a metallic cofactor, coenzyme, or both in order for it to act as a catalyst.
• Amino acids comprise specific active sites that arise due to the folding of the protein (enzyme).

Enzyme-Substrate Interactions

• Substrates specifically bind to the active sites on the enzyme, in a "lock-and-key" or induced fit manner.
• Completion of the reaction sees the release of the resultant product, allowing for the reuse of the enzyme

Cofactors in Enzymes

• Cofactors bind to and activate the enzyme.
• Metallic cofactors example include iron, copper, and magnesium.
• Coenzymes are transient carriers that alter a substrate by moving a chemical group, vitamins are an example

Enzyme Actions

• Exoenzymes, active upon release, initially are not active while inside the cell,
• Endoenzymes remain active inside the cell.
• Constitutive enzymes exist in consistent amounts.
• Regulated enzymes, on the other hand, can either be induced or repressed.

Transfer Reactions

• Condensation is forming a glycosidic bond between two glucose molecules to generate maltose requires the removal of a water molecule and energy from ATP and are associated with anabolic reactions.
• Hydrolysis is breaking a peptide bond between two amino acids requires a water molecule that adds an H and OH to the amino acids and are associated with catabolic reactions.
• Transfer reactions involve the transfer of electrons between substrates through oxidation and reduction, done by oxidoreductase.
• Transfer of functional groups from one molecule to another occurs by transferases such as aminotransferases.

Enzyme Regulation

• Regulation occurs through metabolic pathways, direct control and genetic control
• Metabolic pathways are regulated by the enzymes that catalyze the reactions
• The multienzyme systems follow linear, cyclic, branched, divergent, and convergent patterns.
• Direct control includes competitive and oncompetitive inhibition

Genetic Enzyme Control

• Genetic control is achieved by repression and induction
• Repression happens when end products can stop the expression of genes that encode for proteins (enzymes) responsible for metabolic reactions.
• Enzyme characteristics include being composed of protein, acting as organic catalysts, and lowering activation energy.
• Enzymes have unique characteristics (shape, specificity, function), allow for metabolic reactions at a life-compatible speed.
• Enzymes provide an active site for target molecules and closely associate with substrates, can be recycled and are affected by temperature, pH, and regulated by feedback and genetic mechanisms

Energy

• Cell energetics, redox reactions, electron carriers, and adenosine triphosphate (ATP) are crucial.

Cell Energetics

• Cell energetics involve exergonic and endergonic processes.

Redox Reaction

• Redox reactions are reduction and oxidation reactions
• Electron carriers transport electrons and hydrogens, including electron donors and acceptors.
• Energy in the form of ATP is transferred and captured by the phosphate.

Electron Carriers

• Electron carriers include coenzymes like nicotinamide adenine dinucleotide (NAD)
• Respiratory chain carriers such as Cytochromes (protein) are examples of electron carriers.
• Electron carriers, like NAD, receive electrons and hydrogens from the substrate (organic molecule).

Adenosine Triphosphate (ATP)

• ATP has a temporary energy repository, breaking of phosphates bonds will release free energy
• ATP is a three-part molecule with a nitrogenous base, 5-carbon sugar (ribose), and a chain of phosphates.
• The phosphates captures the energy being released and becomes part of the ATP molecule.
• ATP is used to phosphorylate an organic molecule such as glucose during catabolism.
• ATP is synthesized via substrate-level phosphorylation.

Carbohydrate Catabolism

• Numerous organisms catabolize carbohydrates, like glucose, as an energy source
• Carbohydrates undergo oxidation, used in anabolic reactions,.
• Cellular respiration and fermentation are the two processes for glucose catabolism.

Pathways

• Key catabolic pathways: Embden-Meyerhof-Parnas (EMP) pathway or Glycolysis, Tricarboxylic acid cycle (TCA), Respiratory chain (aerobic and anaerobic), Alternate pathways, Fermentation
• Metabolic strategies for heterotrophic microorganisms growing on glucose involves aerobic respiration, anaerobic metabolism, fermentation and respiration

Glycolysis

• Glucose oxidation with intermediates undergoing phosphorylation (using two ATPs)
• Six carbon split into two 3-carbon sugars
• The net production is two ATP and two pyruvic acid molecules, NAD is reduced to NADH, and water is generated.

TCA Cycle

• Every pyruvic acid gets processed to enter the TCA cycle (two complete cycles).
• Critical intermediates are synthesized, coenzymes NAD and FAD get reduced to NADH and FADH2, also CO2 is generated and two ATPs.

Electron Transport

• NADH and FADH2 donates electrons to the electron carriers, membrane bound carriers then transfer the elections using redox reaction
• The final electron acceptor, like oxygen, completes the terminal step
• Electron transport chain uses Mitochondria on eucaryotes, and cytoplasmic membrane of procaryotes
• The process leads to Chemiosmosis and proton motive force (PMF).

Aerobic and Anaerobic Reactions

• Fermentation yields small amounts of partial ATPs
• Aerobic yields 42 - 2 ATP, with aerobic respiration comprising glycolysis, the tricarboxylic acid (TCA) cycle, and electron transport.
• Glycolysis begins the cycle (two ATP’s generated), followed by the TCA cycle and ultimately ending with electron transport.
• Anaerobic respiration similar to aerobic respiration, however using nitrite or nitrate as the final electron acceptor.

Fermentation

• Occurs when cells cannot entirely oxidize the glucose by cellular respiration.
• Fermentation pathways provide constant cells that uses NAD+
• Requires ongoing supplies of NAM+ for partial oxidation of sugar or metabolites.
• NAD+ supplies are dependent on metabolizing large quantities of glucose during fermentation
• Processes rely on final electron acceptor

Types of Fermentation

• Key processes involving glycolysis only
• Occurs when there is final electron acceptor for electron transport needed, which has the final step of using electron transport that completes the terminal step (ex. Oxygen)
• NADH from glycolysis then gets utilized to reduce resultant organic products.
• Organic compounds act as the concluding electron receivers.
• Includes alcoholic, acidic, and mixed acid fermentation with some facultative anaerobic bacteria
• Some are strict fermentation like yeast

Biosynthesis

• Biosynthesis is anabolism, involves amphibolic reactions, gluconeogenesis, beta oxidation, amination, transamination, deamination and requires marcomolecules

Amphibolicism

• Integrates catabolic and anabolic pathways, intermediates serve multiple purposes,

Biosynthesis Reactions

• Amino acids use amination, where pyruvic acids is converted to B-alanine
• During transamination Aspartic acid get conversted to Glutamic acid
• Deamination converts Glutamic acid to a-ketoglutaric acid
• Intermediates serve to synthesize amino acids, carbohydrates and lipids from the reactions of glycolysis, the TCA cycle using simple products like NH3, CO2, H2O
• Gluconeogenesis converts pyruvate into glucose when the glucose supply is limited.
• Beta oxidation is the Metabolism of fats into acetyl can then enter the TCA cycle as acetyl CoA.

Macromolecules

• Cellular building blocks include monosaccharides, amino acids, fatty acids, nitrogen bases, and vitamins.

Explore microbial metabolism, covering catabolism, anabolism, and the role of enzymes in energy production and biosynthesis. Learn how microbes control biochemical reactions for reproduction. Understand the differences between catabolic (exergonic) and anabolic (endergonic) pathways.