Metabolism and Energy Production in Microbial Cells

Metabolism: Fueling Cell Growth

Dr. Romain - BIO 2215
A foundational topic for understanding numerous biological processes.

Overview of Microbial Metabolism

• Microbial metabolism products are frequently encountered in daily life.

• Essential functions:

  • Production of macromolecules

  • Breakdown of nutrients

  • Cell division requires metabolism.

Fundamentals of Metabolism

• Metabolism is the total of chemical reactions involving:

  • Biosynthesis: Synthesis of new components.

  • Energy Harvesting: Production of ATP.

• The sum of these reactions is termed metabolism.

Key Questions to Consider

• What is energy? Why do cells need it and how is it generated?

• What role do enzymes play in metabolism?

• How are metabolic pathways regulated?

• Understand the processes of:

  • Aerobic respiration

  • Anaerobic respiration

  • Fermentation

  • Photosynthesis (energy generation and usage).

Principles of Metabolism

• Components of Metabolism:

  • Divided into two sections:

  • Anabolism:

    • Involves the synthesis of cell components.

    • Requires energy.

  • Catabolism:

    • Involves degradative reactions that produce energy from larger molecule breakdown.

Macromolecules Involved

• Components Used in Anabolism:

  • Nucleic acids, proteins, polysaccharides, lipids, fats, storage, and membranes.

• Catabolic Pathways:

  • Breaking down molecules into nucleotides, amino acids, carbohydrates, fatty acids, etc.

Metabolic Pathways

• Each pathway is a sequence of chemical reactions.

  • Starting compound converted into intermediates and ultimately end products.

  • Intermediates serve as precursor metabolites for anabolism.

  • Metabolic pathways need key components:

  • ATP/Energy

  • Enzymes

  • Chemical energy sources

  • Electron carriers.

Types of Metabolic Pathways

• Linear Pathway:

  • Sequence follows a straight line of conversion.

• Branched Pathway:

  • Multiple intermediates and end products branching from a single point.

• Cyclic Pathway:

  • End product is recycled into the pathway.

Energy Concepts

• Definition of Energy:

  • The capacity to do work.

• Cells must maintain a constant energy supply for life processes.

• Organisms source energy from:

  • The sun (photosynthesizers)

  • Chemical bonds (chemoorganotrophs).

ATP: Energy Currency

• ATP (Adenosine Triphosphate):

  • The primary energy currency in cells.

  • Produced through three mechanisms:

  • Substrate phosphorylation

  • Oxidative phosphorylation

  • Photophosphorylation.

Mechanisms of ATP Formation

• Substrate Phosphorylation:

  • Phosphate added to ADP using chemical energy.

• Oxidative Phosphorylation:

  • Uses proton motive force to attach a phosphate to ADP.

• Photophosphorylation:

  • Uses light energy for phosphorylation of ADP.

• Chemoorganotrophs rely on substrate and oxidative phosphorylation; photosynthetic organisms use photophosphorylation.

Enzymes in Metabolism

• Enzymes act as catalysts in metabolic pathways.

  • Facilitate conversion of substrates to products by lowering activation energy (AE).

  • Activation Energy: Energy needed to initiate a chemical reaction.

  • Enzymes increase reaction rates without undergoing alteration or being consumed.

Enzyme Mechanism

• Enzyme-Substrate Complex Formation:

  • Enzyme (E) binds to substrate (S), forming ES.

  • Product (P) is released, and the enzyme remains unchanged (E + S → ES → E + P).

Factors Affecting Enzyme Activity

• Enzymes function optimally within specific environmental ranges:

  • Temperature

  • pH

  • Salt Concentration.

Regulation of Enzymes

• Competitive Inhibition:

  • Competing molecules hinder substrate binding to the active site.

• Noncompetitive Inhibition:

  • Binding at a regulatory site alters active site shape, preventing substrate binding.

• Feedback Inhibition:

  • End products inhibit earlier enzymes in pathways to regulate flow.

Cofactors and Coenzymes

• Enzymes may require non-protein components (cofactors) such as metal ions:

  • Examples: Magnesium, Zinc, Copper.

• Coenzymes: Organic cofactors that aid in molecule/electron transfer, such as NAD+, NADP+, and FAD.

Enzymes and Disease

• Pathogens often produce exoenzymes (e.g., diphtheria toxin, cholera toxin) that evade host defenses or promote tissue proliferation, enhancing disease-causing capability.

Summary of Metabolic Pathways

• Metabolic reactions can be broken down into:

  • Catabolic processes: Break down complex molecules (e.g., glucose to pyruvate) producing ATP and other components.

  • Anabolic processes: Build complex molecules from simpler ones, utilizing ATP and reducing power.

Energy Sources and Terminal Electron Acceptors

• Prokaryotes utilize diverse energy sources, including organic/inorganic compounds and various terminal electron acceptors.

• Oxidation-reduction (redox) reactions play a crucial role:

  • Oxidation: Loss of electrons/energy (dehydrogenation).

  • Reduction: Gain of electrons/energy (hydrogenation).

Role of Electron Carriers

• Electrons are carried through various carriers, providing reducing power required for ATP synthesis and biosynthesis.

Catabolic Pathways Yield

• Catabolic pathways provide:

  • Energy, reducing power, precursor molecules.

• Breakdown of glucose involves glycolysis, TCA cycle, and ultimately produces ATP through oxidative phosphorylation or fermentation.

Fermentation

• Occurs when respiration is not an option:

• Converts pyruvate into various products like lactate or ethanol due to limited conditions.

Photosynthesis Overview

• Light energy is captured to produce ATP and organic compounds from CO2.

  • Light Reactions: Produce ATP and NADPH.

  • Dark Reactions (Calvin Cycle): Use ATP/NADPH to fix carbon and produce organic compounds.

Summary Points

• All chemical reactions in cells comprise metabolism, requiring enzymes for activation.

• Energy (ATP) is essential for constructing macromolecules and is produced through various respiration processes and photosynthesis.