Metabolism and Enzymatic Reactions

Metabolism: Overview and Definitions

  • Metabolism: The sum of all chemical reactions that occur within a cell, necessary for cellular functioning and physiology.

    • Focuses on vocabulary related to metabolism.

    • Types of chemical reactions in cells discussed: catabolic and anabolic pathways.

    • Importance of enzymes in facilitating these reactions.

    • Detailed discussion on ATP production is anticipated.

Definitions of Key Terms in Metabolism

  • Catabolic Pathways:

    • Definition: Pathways that break down larger molecules into smaller ones (monomers), releasing energy in the process.

    • Role: Generate energy and building blocks necessary for cellular functions.

    • Examples of substrates: polysaccharides, monosaccharides, proteins.

  • Anabolic Pathways:

    • Definition: Pathways that build larger molecules from smaller ones, requiring energy input.

    • Role: Synthesize macromolecules needed for cellular functions (e.g., proteins, nucleic acids, carbohydrates).

  • Comparison of Catabolic and Anabolic Pathways:

    • Catabolism is associated with breaking down molecules; it is energy releasing.

    • Anabolism is associated with building up molecules; it is energy consuming.

    • Both pathways are tightly regulated as cells aim to conserve energy and materials.

    • Both are essential for cell survival and require enzymatic actions.

Role of Enzymes in Metabolism

  • Enzymes:

    • Definition: Proteins that catalyze specific chemical reactions.

    • Catalysis: The acceleration of a reaction to make it energetically favorable.

    • Example: Lighter fluid acts as a catalyst by facilitating combustion.

  • Activation Energy:

    • Definition: The minimum energy required for a chemical reaction to occur.

    • Enzymes lower the activation energy, allowing reactions to occur more easily and quickly.

  • Mechanism of Enzyme Action:

    • Enzymes bind to substrates at the active site, leading to an induced fit.

    • The induced fit alters the enzyme's structure to enhance catalytic action.

    • Enzymatic reactions result in the transformation of substrates into products without permanently altering the enzyme.

Cofactors and Substrates

  • Cofactors:

    • Definition: Inorganic molecules (e.g., metal ions) that assist in enzyme functions by activating or enhancing enzymatic activity.

  • Substrates:

    • Definition: The specific target molecules upon which enzymes act to produce products.

Enzyme Structure and Function

  • Protein Structure and DNA:

    • Enzymes, being proteins, are sourced from the DNA's coded information.

    • Any mutation in DNA that leads to faulty proteins can impede enzyme functions, potentially causing diseases.

  • Active Site:

    • The region of the enzyme where substrate binding occurs and catalysis takes place.

    • The structure of the active site is crucial for substrate specificity, ensuring only particular substrates can bind efficiently.

Specificity of Enzymes

  • Enzyme Specificity:

    • Enzymes exhibit selectiveness for specific substrates; not all substrates can bind to all enzymes.

    • This specificity is crucial for accurate metabolic regulation.

Factors Influencing Enzyme Activity

  • Enzyme Concentration:

    • Increased enzyme concentration results in a higher reaction rate, assuming substrate concentration is sufficient.

  • Substrate Concentration:

    • Excess substrate can overwhelm enzyme binding sites, affecting reaction rates.

  • Temperature:

    • Higher temperatures may lead to denaturation of enzymes, disrupting their structure and function.

    • Cooling enzymes can slow down metabolic processes due to reduced kinetic activity.

  • pH Levels:

    • Each enzyme has an optimal pH range; deviations can affect enzyme activity and structural integrity.

Naming of Enzymes

  • Enzymes typically end with the suffix -ase, indicating enzymatic action.

    • Examples of enzyme classes:

    • Proteases: Break down proteins.

    • Lipases: Break down lipids.

    • Amylases: Break down starches.

    • Catalase: Breaks down hydrogen peroxide into water and oxygen.

    • Lysozyme: Cleaves polysaccharide chains in bacterial cell walls, acting as an antimicrobial substance.

Classes of Enzymes

  • Hydrolases:

    • Catalyze hydrolysis, breaking chemical bonds through the addition of water.

  • Isomerases:

    • Catalyze rearrangements of bonds within a molecule, producing isomers.

  • Ligases:

    • Form covalent bonds between two molecules, often using ATP.

  • Lysases:

    • Cleave bonds without using water, differing from hydrolases.

  • Oxido-reductases:

    • Transfer electrons between electron donors (oxidants) and acceptors (reductants).

    • Important for energy movement in metabolic processes, often referred to as redox reactions.

  • Transferases:

    • Transfer functional groups (e.g., phosphate, methyl) from one molecule to another.

    • Example: Kinases transfer phosphate groups to substrates, essential for many metabolic processes.

Oxidation-Reduction Reactions

  • Oxidation-Reduction (Redox) Reactions:

    • Involve the transfer of electrons; crucial for metabolism and energy generation.

    • Definitions:

    • Electron Acceptor: Gains electrons, reducing its overall charge (becomes more negative).

    • Electron Donor: Loses electrons (oxidized).

    • Mnemonic: OIL RIG - Oxidation Involves Loss; Reduction Involves Gain.

  • Role of NAD/NADH:

    • Major energy carriers in metabolic pathways.

    • NAD (oxidized form) can accept electrons and become NADH (reduced form), carrying energy-rich electrons.

    • NADH cycles between reduced and oxidized states, facilitating electron transfer in metabolic processes, particularly cellular respiration.