Microbial Metabolism

Definition of Metabolism

Metabolism refers to the sum of all chemical reactions that occur within a living organism. These reactions are essential for maintaining life, providing energy, and synthesizing cellular components.

• Metabolism: The totality of an organism's chemical processes.

• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy.

• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy input.

• Example: Glucose catabolism provides energy for ATP synthesis; protein synthesis is an anabolic process.

Enzymes and Their Role in Chemical Reactions

Enzymes are biological catalysts that accelerate chemical reactions by lowering the activation energy required. They are highly specific for their substrates and are essential for metabolic pathways.

• Apoenzyme: The protein portion of an enzyme, inactive without its cofactor.

• Cofactor: Non-protein component (often a metal ion or coenzyme) required for enzyme activity.

• Holoenzyme: The complete, active enzyme consisting of the apoenzyme plus its cofactor.

• Enzyme Classes:

  • Hydrolase: Catalyzes hydrolysis reactions.

  • Lyase: Catalyzes removal of groups without hydrolysis.

  • Ligase: Catalyzes joining of two molecules.

  • Transferase: Transfers functional groups between molecules.

  • Isomerase: Catalyzes isomerization changes within a molecule.

  • Oxidoreductase: Catalyzes oxidation-reduction reactions.

• Example: DNA polymerase (a ligase) joins nucleotides during DNA replication.

Oxidation and Reduction

Oxidation and reduction (redox) reactions are fundamental to energy transfer in cells. Oxidation involves loss of electrons, while reduction involves gain of electrons.

• Oxidation: Loss of electrons or hydrogen; gain of oxygen.

• Reduction: Gain of electrons or hydrogen; loss of oxygen.

• Example: NAD+ is reduced to NADH during glycolysis.

Cellular Respiration and Fermentation

Comparison of Cellular Respiration and Fermentation

Both processes generate ATP, but differ in their mechanisms and efficiency.

• Cellular Respiration: Complete oxidation of glucose to CO2 and H2O, using oxygen as the final electron acceptor.

• Fermentation: Partial oxidation of glucose, does not require oxygen, produces organic end products (e.g., lactic acid, ethanol).

• Example: Yeast performs alcohol fermentation; muscle cells perform lactic acid fermentation.

Glycolysis

Glycolysis is the first step in glucose catabolism, occurring in the cytoplasm.

• Glucose is converted to two molecules of pyruvate.

• Net production of 2 ATP and 2 NADH per glucose.

• Equation:

Krebs Cycle (Citric Acid Cycle)

The Krebs cycle completes the oxidation of glucose derivatives, generating NADH, FADH2, and ATP.

• Occurs in the cytoplasm of prokaryotes and mitochondria of eukaryotes.

• Produces CO2, NADH, FADH2, and ATP.

• Equation:

Role of Oxygen in Cellular Respiration

Oxygen acts as the terminal electron acceptor in the electron transport chain, allowing for maximal ATP production.

• Without oxygen, cells switch to fermentation.

• Oxygen is reduced to water at the end of the electron transport chain.

Lactic Acid vs. Alcohol Fermentation

Fermentation pathways differ in their end products and organisms.

• Lactic Acid Fermentation: Pyruvate is reduced to lactic acid; occurs in bacteria and muscle cells.

• Alcohol Fermentation: Pyruvate is converted to ethanol and CO2; occurs in yeast.

• Example: Lactobacillus produces lactic acid; Saccharomyces cerevisiae produces ethanol.

Cellular Respiration Location

• Prokaryotes: Glycolysis and Krebs cycle in cytoplasm; electron transport chain in plasma membrane.

• Eukaryotes: Glycolysis in cytoplasm; Krebs cycle and electron transport chain in mitochondria.

Enzyme Regulation and Inhibition

Effects of Temperature and pH

Enzyme activity is sensitive to environmental conditions.

• Optimal temperature and pH maximize enzyme activity.

• Extreme conditions can denature enzymes, reducing activity.

• Example: Human enzymes function best at 37°C and pH 7.4.

Enzyme Inhibitors

• Competitive Inhibitors: Bind to the active site, blocking substrate access.

• Non-Competitive Inhibitors: Bind to an allosteric site, changing enzyme shape and reducing activity.

• Example: Sulfa drugs act as competitive inhibitors of folic acid synthesis in bacteria.

ATP Production and Electron Transport Chain

Oxidative Phosphorylation

Oxidative phosphorylation is the process by which ATP is generated using energy from electrons transferred through the electron transport chain.

• Occurs in the inner mitochondrial membrane (eukaryotes) or plasma membrane (prokaryotes).

• Involves ATP synthase enzyme.

• Equation:

Electron Transport Chain (ETC) and ATP Synthase

The ETC consists of a series of protein complexes that transfer electrons, creating a proton gradient used by ATP synthase to generate ATP.

• Electrons from NADH and FADH2 are passed through complexes.

• Protons are pumped across the membrane, creating a gradient.

• ATP synthase uses this gradient to synthesize ATP.

Metabolic Pathways and Biosynthesis

Deamination

Deamination is the removal of an amino group from amino acids, allowing their carbon skeletons to enter metabolic pathways.

• Produces ammonia as a waste product.

• Allows amino acids to be used for energy or biosynthesis.

Polysaccharide Biosynthesis

Polysaccharides are synthesized from monosaccharides via glycosidic bonds, important for cell wall and energy storage.

• Requires energy input (usually ATP).

• Example: Synthesis of peptidoglycan in bacterial cell walls.

Lipid Biosynthesis

Lipids are synthesized from acetyl-CoA and glycerol, essential for membrane structure and energy storage.

• Fatty acids are elongated and joined to glycerol.

• Example: Phospholipid synthesis for cell membranes.

Purine and Pyrimidine Biosynthesis

Purines and pyrimidines are synthesized via complex pathways, including the pentose-phosphate and Entner-Doudoroff pathways. Amino acids contribute to their formation.

• Pentose-phosphate pathway provides ribose sugars.

• Entner-Doudoroff pathway is an alternative to glycolysis in some bacteria.

• Amino acids (e.g., glutamine, aspartate) are precursors for nucleotide bases.

Photosynthesis

Differences Between Cellular Respiration and Photosynthesis

Photosynthesis and cellular respiration are complementary processes.

• Cellular Respiration: Converts glucose and oxygen to CO2 and water, releasing energy.

• Photosynthesis: Converts CO2 and water to glucose and oxygen, using light energy.

Light-Dependent Reactions and Calvin-Benson Cycle

Photosynthesis consists of light-dependent reactions and the Calvin-Benson cycle.

• Light-Dependent Reactions: Occur in thylakoid membranes; produce ATP and NADPH.

• Calvin-Benson Cycle: Occurs in stroma; uses ATP and NADPH to fix CO2 into glucose.

Microbial Nutrition and Classification

Definitions: Phototroph, Chemotroph, Autotroph, Heterotroph

• Phototroph: Uses light as energy source.

• Chemotroph: Uses chemicals as energy source.

• Autotroph: Uses CO2 as carbon source.

• Heterotroph: Uses organic compounds as carbon source.

• Example: Cyanobacteria are photoautotrophs; Escherichia coli is a chemoheterotroph.

Summary Table: Metabolic Pathways and Properties

Additional info: Academic context was added to expand brief points into full explanations, including examples, equations, and a summary table for clarity.