Metabolism

• Metabolism is the totality of an organism's chemical reactions and is an emergent property of life
• A metabolic pathway begins with a specific molecule which is altered in a series of defined steps, resulting in a certain product. Each step is catalysed by a specific enzyme. Catabolic pathways release energy while anabolic pathways consume energy
• Work is the ability to move matter against opposing forces and in biology, this depends on the ability of cells to transform energy
• Energy is the capacity to do work and in biological terms this is the ability to rearrange a collection of matter.

  • Kinetic energy is energy of motion
  • Heat energy is kinetic energy associated with random movement of atoms
  • Light energy powers photosynthesis
  • Potential energy is non-kinetic energy and is possessed due to location or structure
  • Chemical energy is potential energy for release in a reaction
• Thermodynamics is the study of energy transformations that occur in a collection of matter
• 1st Law of Thermodynamics: 'Energy can neither be created nor destroyed but can be converted from one form to another'
• 2nd Law of Thermodynamics: "Every energy transfer or transformation increases the disorder of the universe"
• Entropy - Disorder, quantity if energy is constant but quality is not
• Free energy (G) is the portion of a systems energy that can perform work when temperature is uniform throughout the system
• G = H - TS

  where G is free energy, H is the total energy in the system, T is the temp in Kelvin, and S is entropy
• In an exergonic reaction, energy is released
• In an endergonic reaction, free energy is absorbed
• Exergonic and endergonic reactions are coupled in cells
• ATP is the intermediate source of energy and mediates most energy coupling in cells
• A cell does 3 kinds of work: chemical eg. polymer synthesis, transport eg. active transport, and mechanical eg. beating of cilia
• ATP is made up of a nitrogenous base, ribose, and 3 phosphates
• Energy from hydrolysis of ATP fuels reactions
• Cells use ATP by using enzymes to transfer phosphate groups from ATP to other molecules. Phosphorylation primes the molecule to perform work.
• Enzymes speed up metabolic reactions by lowering energy barriers and acting as catalysts.
• Reactants must absorb energy to start a reaction which is often supplied in the form of heat.
• Enzymes have substrate specificity due to structural complementarity and bind substrate only at the active site which enfolds the substrate due to the induced fit model.
• The rest of the protein provides a framework that determines the configuration of the active site.
• Each enzyme has an optimal temperature and pH to avoid disruptions to bonds.
• Many require inorganic or organic cofactors such as metal atoms, coenzymes.
• Most vitamins are coenzyme precursors.
• Inhibitors bind to enzymes to inactivate them while allosterical regulators bind to stabilise forms.
• Feedback inhibition occurs when a metabolic pathway is switched off by its end product
• Protein kinases catalyse phosphorylation (the transfer of phosphate groups from ATP to proteins)
• Delta G = G - G0