Metabolism

• Metabolism

  Sum of all chemical reactions and energy transformations in an organism
• Metabolism


  • Emergent property of life
  • Arises from orderly interaction between molecules
• Types of metabolic processes


  • Anabolic (synthetic)
  • Catabolic (degradative)
• Anabolic reactions


  Synthetic, convert simple to complex, require energy
• Catabolic reactions


  Degradative, convert complex to simple, release energy
• Metabolism is regulated, with anabolic processes greater than catabolic processes for homeostasis
• Energy


  Capacity to do work
• Forms of energy

  • Potential (stored)
  • Kinetic (motion)
• Laws of thermodynamics


  • Energy cannot be created or destroyed, only converted from one form to another
  • Energy transformations are not 100% efficient, some is lost as heat
• Every energy transformation increases entropy (disorder)
• Radiant energy from the sun


  Ultimate source of energy for most organisms
• Food

  Source of energy for heterotrophs
• Types of cellular work


  • Mechanical (e.g. cilia)
  • Transport (e.g. across membranes)
  • Chemical (e.g. synthesis)
• Free energy (G)


  Energy that is available to do work
• Change in free energy (ΔG)


  Determines whether a chemical reaction will release or require energy
• Types of chemical reactions

  • Exergonic (energy outward)
  • Endergonic (energy inward)
• Exergonic reactions


  Reactants have more potential energy than products, so energy is released
• Endergonic reactions


  Reactants have less potential energy than products, so energy input is required
• ATP (adenosine triphosphate)


  High-energy compound with three phosphate groups that can be hydrolyzed to release energy
• Activation energy (EA)


  Energy needed to start a chemical reaction, even for exergonic reactions
• Enzymes

  • Biological catalysts that lower the activation energy barrier
  • Speed up the rate of reactions in cells without being consumed
• Enzyme specificity

  Enzymes only work on one type of molecule (substrate)
• Irreversible enzyme inhibition


  Enzyme is destroyed or inactivated by the inhibitor
• Anabolic pathways


  Require energy to synthesize complex molecules from simpler ones
• Catabolic pathways


  Release energy when complex molecules break down
• Chemical bonds' breakdown can release energy, implying those bonds have potential energy
• There is potential energy stored within the bonds of all the food molecules we eat, which we eventually harness for use
• Chemical energy

  The potential energy type that exists within chemical bonds that releases when those bonds break
• Chemical energy is responsible for providing living cells with energy from food
• Breaking the molecular bonds within fuel molecules brings about the energy's release
• Gibbs free energy (G)


  A measurement of free energy used to quantitate energy transfers
• According to the second law of thermodynamics, all energy transfers involve losing some energy in an unusable form such as heat, resulting in entropy
• Gibbs free energy


  The energy that takes place with a chemical reaction that is available after we account for entropy, or usable energy
• Delta G (∆G)


  The change in free energy for a chemical reaction
• Exergonic reactions


  Reactions that have a ∆G < 0 and consequently release free energy
• Endergonic reactions


  Reactions that have a ∆G > 0 and require an energy input rather than releasing energy
• Activation energy (EA)


  The small amount of energy input necessary for all chemical reactions to occur
• During chemical reactions, certain chemical bonds break and new ones form
• Transition state


  A high-energy, unstable state that reactant molecules must reach to allow the bonds to break
• Free energy diagrams illustrate the energy profiles for a given reaction