Energy Production: Mitochondria

• Mitochondria


  Energy production
• Main features of mitochondria

  • Large organelles
  • Easily visible using light microscopes
  • First identified in the 19th century
  • Remarkably plastic
  • Can change shape and move around the cell
  • Can fuse with one another
• The number of mitochondria per cell varies according to the energy requirements of the cell
• Mitochondria structure: main features

  • Two highly specialised membranes
  • Intermembrane space
  • Internal matrix
  • Highly convoluted inner membrane forming cristae
• Cardiolipin


  A lipid found in the inner mitochondrial membrane
• Matrix


  Contains enzymes that metabolise pyruvate and fatty acids
• Reduction


  The addition of an electron (e-)
• Oxidation


  The removal of an electron (e-)
• Hydrogen consists of an electron and a proton
• Energy production: Key Concept 1

  Electrons reduce; Protons (H+) neither reduce nor oxidise
• Energy production: Key Concept 2

  Glucose can be metabolised through oxidation to produce energy (glycolysis)
• 1 molecule of glucose yields a net production of 2 ATP molecules
• Under aerobic conditions, glucose metabolism can increase ATP production to 4 ATP molecules
• Energy production: Key Concept 3

  The citric acid cycle occurs in the mitochondrial matrix and produces reduced electron carriers (e.g. NADH) for the electron transport chain
• Electrons are transferred from NADH or FADH2


  To the electron transport chain
• Energy production: Key Concept 4

  The electron transport chain is in the cristae of the mitochondrion
• Most of the electron transport chain’s components are proteins
• Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O
• The cytochrome oxidase complex accounts for around 90% of the total oxygen uptake in most cells
• Cyanide is extremely toxic because it binds tightly to the cytochrome oxidase complex, stopping electron transport and greatly reducing ATP production
• Cytochrome C


  Plays a crucial role in the regulation of cell death
• Carriers of electrons


  • FeS (iron sulphur proteins)
  • Cytochromes
• Carriers of electrons + H+

  • FMN (flavin mononucleotide)
  • FAD (flavin adenine dinucleotide)
  • Q (ubiquinone)
  • Oxygen
• Energy production: Key Concept 5

  ATP synthesis is coupled to electron transport
• ATP synthase is a multi-subunit protein with a mass of more than 500,000 Da that is responsible for producing ATP
• How ATP synthase works

  1. ADP + Pi -> ATP

  2. Chemiosmosis: the energy coupling mechanism
• Uncoupling proteins (UCPs)


  • Mitochondrial transporters
  • Present in the inner membrane of mitochondria
  • Found in all mammals and in plants
  • Present in mitochondria of brown adipocytes (fat cells)
• Mitochondrial uncoupling


  Dissipates energy of substrate oxidation as heat
• Mitochondrial uncoupling also allows

  Continuous reoxidation of coenzymes that are essential to metabolic pathways
• Mitochondrial uncoupling priorities


  • Heat generation
  • Energy conservation
• Mitochondrial membrane types


  • Proton leaky
  • Proton non-leaky
• Respiration-ATP types


  • Uncoupled
  • Well-coupled
• Mitochondrial uncoupling is involved in hibernation