Microbial Metabolism Quiz

Microbial Metabolism

• Microbial metabolism encompasses the biochemical reactions for energy generation (catabolism) and biosynthesis (anabolism).
• Catabolism releases energy, often stored as ATP (adenosine triphosphate).
• Anabolism consumes energy, utilizing ATP.
• Metabolic pathways are series of enzyme-catalyzed reactions.
• Enzymes accelerate reactions without being consumed, lowering activation energy.

Nutritional Requirements

• Essential elements for bacterial growth include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S).
• Minerals like potassium, calcium, magnesium, iron, copper, cobalt, manganese, molybdenum, and zinc are needed in trace amounts.

Enzyme Activity Control

• Enzyme activity is controlled by:
  • Enzyme and substrate concentration.
  • Temperature, pH, and salt concentration.
  • Cofactor availability.
  • Inhibitors (competitive, binding to the active site; allosteric, binding elsewhere).
• Enzyme denaturation occurs when changes in temperature, pH, or salt concentration disrupt the protein's structure.
• Mutations can also lead to misfolded, non-functional enzymes.

Redox Cofactors

• Redox reactions often require cofactors like NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) to shuttle electrons.
• NAD and FAD are regenerated to maintain metabolism.
• Cofactors can be metal ions, vitamins, or other non-protein molecules. If organic, they're called coenzymes (often vitamins).

ATP and Glycolysis

• ATP is the preferred energy source for all cells; breaking the bond of its third phosphate releases energy.
• Glycolysis catabolizes sugars (like glucose) into two 3-carbon pyruvate molecules, yielding 2 ATP and 2 NADH per glucose.

Glycolytic Pathways

• Four major glycolytic pathways exist in bacteria:
  • Embden-Meyerhof-Parnas (EMP) pathway: Glucose → 2 pyruvate + 2 ATP + 2 NADH. Common in many organisms.
  • Pentose phosphate pathway (also called hexose monophosphate pathway): Generates NADPH and pentose phosphates for nucleotide synthesis. Glucose 6-phosphate + 2 NADP+ + H2O → ribulose 5-phosphate + 2 NADPH + 2H+ + CO2
  • Entner-Doudoroff pathway: Glucose → 2 ethanol + 2 CO2 + 1 ATP; used by bacteria lacking some glycolysis enzymes.
  • Phosphoketolase pathway: Glucose → 1 lactate + 1 ethanol + 1 CO2 + 1 ATP; used in dairy fermentation.

Fermentation

• Organisms recycle NAD+ through various fermentation pathways, producing diverse end products:
  • Lactic acid fermentation (e.g., Streptococcus, Lactobacillus)
  • Mixed acid fermentation (e.g., Escherichia coli)
  • 2,3-Butanediol fermentation (e.g., Enterobacter aerogenes)

Respiration and Chemiosmosis

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ATP Production Summary

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Photosynthesis

• Autotrophs produce organic molecules from inorganic carbon (CO2); heterotrophs require organic carbon sources.
• Energy sources for autotrophs include:
  • Light (photoautotrophs, performing photosynthesis)
  • Chemicals (chemoautotrophs)

Light-Dependent Reactions: Photophosphorylation

• Light energy is harvested by pigments, transferred to chlorophyll reaction centers (photosystems).
• Light energy strips electrons from a donor, shuttling them through electron carriers to generate ATP.
• Cyclic pathways return electrons to the transport chain; non-cyclic pathways use them to reduce NAD(P) to NAD(P)H.

Dark Reactions (CO2 Fixation)

• ATP and NADPH from the light reactions drive CO2 fixation via the Calvin cycle to form carbohydrates.
• These reactions produce key monomers for anabolic reactions.

Oxygenic vs. Anoxygenic Photosynthesis

• Oxygenic photosynthesis (cyanobacteria, chloroplasts): Uses H2O as an electron donor, producing O2; involves two photosystems (PSII and PSI).
• Anoxygenic photosynthesis (various bacteria): Electron donors vary (H2S, SO, H2, or organic compounds); typically involves a single photosystem, mainly for ATP production via cyclic photophosphorylation.