Microbes rely on metabolism to survive and thrive. They break down complex molecules for energy and build new ones for growth. Some make their own food, while others need organic compounds. Redox reactions power these processes, moving electrons around.

Energy carriers like ATP fuel cellular activities. Enzymes speed up reactions, with their structure determining function. Inhibitors can slow enzymes down. Understanding how microbes generate and use energy is key to grasping their incredible diversity and adaptability.

Metabolism and Energy Acquisition

Role of metabolism in microbes

• Sum of all chemical reactions within a living organism
  • Catabolism breaks down complex molecules releasing energy (glucose breakdown)
  • Anabolism uses energy to synthesize complex molecules from simpler ones (protein synthesis)
• Microbial cells rely on metabolism to generate ATP energy, synthesize essential biomolecules (proteins, nucleic acids, lipids, carbohydrates), and maintain cellular homeostasis

Autotrophs vs heterotrophs

• Autotrophs produce their own organic compounds using inorganic sources
  • Photoautotrophs use light energy to synthesize organic compounds (cyanobacteria, purple sulfur bacteria)
  • Chemoautotrophs use chemical energy from inorganic compounds to synthesize organic compounds (sulfur-oxidizing bacteria, nitrifying bacteria)
• Heterotrophs rely on organic compounds as their energy and carbon source
  • Chemoheterotrophs obtain energy from chemical reactions involving organic compounds (most bacteria, fungi)

Oxidation-reduction in microbial metabolism

• Oxidation-reduction (redox) reactions transfer electrons between molecules
  • Oxidation loses electrons
  • Reduction gains electrons
• Redox reactions crucial in microbial metabolism for generating energy through electron transport chains, driving metabolic pathways (glycolysis, Krebs cycle), and maintaining cellular redox balance

Cellular Energy Processes and Enzymes

Energy carriers in cellular processes

• ATP (Adenosine triphosphate) universal energy currency in living cells stores and transfers energy for cellular processes (biosynthesis, transport, motility)
• FAD (Flavin adenine dinucleotide) coenzyme involved in redox reactions accepts electrons during oxidation reactions (reduced to FADH2) donates electrons to electron transport chain for ATP synthesis
• NAD+ (Nicotinamide adenine dinucleotide) coenzyme involved in redox reactions accepts electrons during oxidation reactions (reduced to NADH) donates electrons to electron transport chain for ATP synthesis
• NADP+ (Nicotinamide adenine dinucleotide phosphate) coenzyme involved in anabolic reactions accepts electrons during oxidation reactions (reduced to NADPH) provides reducing power for biosynthetic reactions

Enzyme structure in microbes

• Enzymes are proteins that catalyze chemical reactions in living cells
• Structure composed of one or more polypeptide chains with specific three-dimensional shape determined by amino acid sequence
• Key components include:
  • Active site region where substrate binds and catalysis occurs
  • Cofactors non-protein molecules required for enzyme function (metal ions, vitamins)
  • Coenzymes organic molecules that assist in enzyme catalysis (FAD, NAD+, NADP+)

Types of enzyme inhibitors

• Enzyme inhibitors are molecules that decrease or stop enzyme activity
• Competitive inhibitors structurally similar to substrate bind to active site preventing substrate binding causing reversible inhibition that can be overcome by increasing substrate concentration affecting $K_m$ (Michaelis constant) but not $V_{max}$ (maximum velocity)
• Noncompetitive inhibitors bind to allosteric site other than active site causing conformational changes that decrease enzyme activity with reversible or irreversible inhibition that cannot be overcome by increasing substrate concentration affecting $V_{max}$ but not $K_m$
• Enzyme inhibition in microbial metabolism can disrupt essential metabolic pathways, impair energy production and cellular growth, and be exploited for development of antimicrobial agents (antibiotics, antifungals)

Thermodynamics and Bioenergetics in Microbial Metabolism

• Thermodynamics governs energy transformations in microbial cells
  • Enthalpy refers to the total heat content of a system, important in understanding energy changes during chemical reactions
  • Entropy measures the degree of disorder in a system, increasing in spontaneous processes
• Bioenergetics applies thermodynamic principles to biological systems
  • Activation energy is the minimum energy required for a reaction to occur, which enzymes lower through catalysis
• Enzyme kinetics studies the rate of enzyme-catalyzed reactions, crucial for understanding metabolic regulation