4.1 Metabolic Pathways

Bioenergetics and Metabolism

  • Bioenergetics: Study of energy flow through living systems.

  • Metabolism: Sum of all chemical reactions in a cell; includes energy consumption and generation.

    • Anabolic pathways: Synthesis of molecules; requires energy.

    • Catabolic pathways: Breakdown of molecules; releases energy.

Metabolic Pathways

  • Metabolic pathway: Sequence of chemical reactions where a starting molecule is modified step-by-step to yield a final product.

  • Enzymes catalyze each step of metabolic pathways.

  • Photosynthesis:

    • 6CO<em>2+6H</em>2O→C<em>6H</em>12O<em>6+6O</em>26CO<em>2 + 6H</em>2O \rightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2

  • Respiration:

    • C<em>6H</em>12O<em>6+6O</em>2→6H<em>2O+6CO</em>2C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6H<em>2O + 6CO</em>2

Thermodynamics

  • Thermodynamics: Study of energy and energy transfer.

  • System: Matter relevant to energy transfer.

  • Surroundings: Everything outside the system.

  • Open system: Exchanges energy with surroundings (e.g., biological organisms).

  • Closed system: Does not exchange energy with surroundings.

    • First law of thermodynamics: Energy is conserved; it can be transferred or transformed, but not created or destroyed.

    • Second law of thermodynamics: Energy transfer is inefficient; some energy is lost as heat, increasing entropy (disorder).

Kinetic and Potential Energy

  • Kinetic energy: Energy of objects in motion.

  • Potential energy: Stored energy (e.g., based on position or structure).

  • Chemical energy: Potential energy stored in chemical bonds.

Free and Activation Energy

  • Free energy (ΔG\Delta G): Usable energy available in a chemical reaction after accounting for losses.

  • Exergonic reactions: Release energy; ΔG\Delta G is negative; spontaneous.

  • Endergonic reactions: Absorb energy; ΔG\Delta G is positive; non-spontaneous.

  • Activation energy: Small amount of energy input required for all chemical reactions to occur.

Enzymes

  • Enzymes: Biological catalysts (usually proteins) that lower activation energy and speed up reactions.

  • Enzymes are unchanged by a reaction and can catalyze other reactions.

  • Substrates: Reactants to which an enzyme binds.

  • Active site: Location on the enzyme where the substrate binds.

  • Induced fit: Enzyme and substrate interaction causes a mild shift in enzyme structure for ideal binding.

  • Enzyme-substrate complex: Formed when an enzyme binds its substrate.

  • Competitive inhibition: Inhibitor binds to the active site, blocking substrate binding.

  • Noncompetitive inhibition: Inhibitor binds to an allosteric site, preventing substrate binding.

  • Allosteric inhibition: Inhibitor binding induces a conformational change that reduces enzyme activity.

  • Allosteric activators: Increase enzyme affinity for its substrate.

  • Cofactors: Inorganic ions that promote optimal enzyme shape and function.

  • Coenzymes: Organic helper molecules that are recycled and reused.

  • Feedback inhibition: Reaction product regulates its own further production.