Respiration

• the outer mitochondrial membrane controls entry and exit of molecules into mitochondria
• the intermembrane space in the mitochondria allows the build up of protons
• the inner mitochondrial membrane has many embedded proteins for the ETC and oxidation phosphorylation
• cristae increase the Surface Area for the ETC and OP
• the matrix is where chemical reactions occur - the Link reaction, the Krebs cycle
• 38 molecules of ATP are formed per glucose in respiration
• respiration: C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy
• respiration is the 4 stage process whereby energy stored in complex organic/biological molecules is transferred to make ATP, which provided the immediate source of energy for metabolic processes
• photophosphorylation is phosphorylation of ADP using an electron transport chain (energy from light) to drive chemiosmosis
• substrate-level phosphorylation is phosphorylation of ADP by directly adding a phosphate group from another molecule
• oxidative phosphorylation (OP) is phosphorylation of ADP using an ETC (energy from high energy electrons in coenzymes rNAD and rFAD) to drive chemiosmosis
• stages of respiration:

  1. Glycolysis - net 2 ATP (SL-P)

  2) The Link reaction - no ATP made (SL-P)

  3) The Krebs cycle - 1 ATP per turn

  4) The electron transport chain - 34 ATP (OP)
• glycolysis occurs in the cytoplasm
• glycolysis is when one glucose is broken down into 2 pyruvates forming 2x ATP and 2x rNAD
• stages of glycolysis: phosphorylation, splitting, oxidation
• phosphorylation:

  • one molecule of glucose is turned into hexose monophosphate by ATP turning into ADP (giving it a phosphate)
  • then hexose monophosphate is turned into hexose bisphosphate by ATP turning into ADP (giving it a phosphate)
• in splitting hexose bisphosphate splits into 2 triose phosphate molecules, 2 phosphates are added from the cytoplasm
• in oxidation the 2 triose phosphate molecules are turned into 2 Pyruvate molecules. 1 NAD is reduced to rNAD and 2x ADP are converted to 2x ATP per pyruvate molecule formed.
• NAD is a coenzyme
• the link reaction occurs in the matrix
• stages in the link reaction: dehydrogenation, decarboxylation, combination with CoA
• in dehydrogenation two oxygens and a carbon are broken off from pyruvate via an enzyme, forming carbon dioxide
• in decarboxylation NAD is reduced to rNAD by a hydrogen from pyruvate by dehydrogenase
• in the final step in the link reaction, the acetyl group left from pyruvate joins to coenzyme A (CoA) forming Acetyl CoA
• link reaction: Pyruvate + NAD + CoA --> Acetyl CoA + CO2 + rNAD
• the link reaction occurs twice per glucose
• the krebs cycle occurs in the matrix
• the Krebs cycle occurs twice per glucose
• krebs cycle steps:

  1. Acetyl CoA is added to Oxaloacetate, forming citrate (a 6 carbon molecule)

  2) citrate is turned into a 5 carbon molecule, releasing a CO2 and reducing NAD to rNAD

  3) the 5 carbon molecule is turned into a 4 carbon molecule, releasing a CO2 and reducing NAD to rNAD

  4) the 4 carbon molecule is converted into Oxaloacetate, a 4 carbon molecule, using ADP + Pi to form ATP, NAD to form rNAD, and FAD to form rFAD

  5) the steps start again as Oxaloacetate joining with Acetyl CoA
• chemiosmosis steps:

  1. energy is released as electrons are passed down a chain of electron carriers

  2) this causes protons to be pumped through the membrane

  3) protons accumulate generating a gradient across the membrane

  4) this causes protons to flow down their concentration gradient through a protein channel

  5) this proton motive force causes a conformational shape change in ATP synthase

  6) this allows ADP and Pi to combine and form ATP
• 4 complexes are involved in the electron transport chain
• the ETC is also known as oxidative phosphorylation
• the ETC occurs in the inner membrane
• at the first complex rNAD is oxidised to NAD as electrons are lost and travel through the membrane to other complexes. H+ ions diffuse through the membrane from the matrix to the intermembrane space through the complex
• in the second complex rFAD is oxidised to FAD, and the electron released is added to the electrons from complex one moving through the membrane
• in the third complex H+ ions moves through the membrane from the matrix into the intermembrane space through the complex (proton pump)
• in the fourth complex O2 is reduced into H2O, using electrons provided by the other complexes. H+ ions move through the membrane from the matrix to the intermembrane space forming an H+ gradient
• the H+ gradient formed due to the complexes results in the H+ ions moving from the intermembrane space into the matrix through ATP Synthase which results in ATP being synthesised from ADP and Pi
• Cytochrome oxidase is complex 4
• reduction of oxygen: oxygen + electrons + protons --> water