Respiration

• Respiration can be done anaerobically and aerobically meaning using oxygen
• Phosphorylation is the addition of a phosphate group from ATP hydrolysis to a molecule
• Oxidative phosphorylation occurs in the electron transport chain where ATP is formed as NADH and FADH are oxidised
• Substrate level phosphorylation occurs when the phosphate is directly added to an ADP molecule to form ATP
• NAD, FAD and coenzyme A are the coenzymes involved in transferring hydrogen ions between molecules in respiration
• Dehydrogenation is the removal of a hydrogen ion
• Decarboxylation is the removal of a carbon molecule forming CO2
• Glycolysis is anaerobic and occurs in the cytoplasm so needs a cell to form pyruvate
• In glycolysis, glucose is phosphorylated twice using 2 ATP to form glucose phosphate and then hexose bisphosphate, hexose bisphosphate then splits into 2 triose phosphates which are oxidised to 2 pyruvate molecules producing 4 ATP and 2 NADH
• The net ATP and NADH gain of glycolysis from 1 glucose molecule is 2 ATP and 2 NADH
• Pyruvate is actively transported across the mitochondrion membrane for the link reaction
• The link reaction occurs in the matrix of the mitochondrion
• In the link reaction, 1 pyruvate is decarboxylated releasing 1 CO2 and 1 NAD is reduced to form acetate (2C), coenzyme A is added, forming acetyl CoA
• Pyruvate produces 1 CO2 and 1 NADH in the link reaction
• Acetyl CoA is used in the krebs cycle where it combines with oxaloacetate, forming citrate and releasing the coenzyme A back to the link reaction
• Once citrate is formed in the krebs cycle, 1 carbon is removed as CO2, 1 NAD is reduced, 1 carbon is removed as CO2, 1 NAD is reduced, 1 ATP is synthesised, 1 FAD is reduced, 1 NAD is reduced, oxaloacetate is formed as a result
• De (decarboxylation) Na (NADH formed) De (decarboxylation) Na (NADH formed) A (ATP synthesised) Fa (FADH formed) Na (NADH formed)
• Coenzyme A is recycled into the link reaction
• The krebs cycle is a cycle because oxaloacetate is produced and then combined with acetyl CoA to restart the cycle
• Oxaloacetate is 4C, acetyl CoA is 2C, citrate is 6C
• NADH produces 2.5 ATP in the electron transport chain, FADH produces 1.5 ATP
• NADH can use all three proton pumps whereas FADH can only use two
• The krebs cycle produces many intermediate compounds used by cells to produce fatty acids and amino acids
• The krebs cycle occurs in the matrix
• Oxidative phosphorylation occurs in the inner membrane of the mitochondrion
• NADH and FADH release hydrogen ions and electrons which are pumped using energy lost by electrons into the intermembrane space through electron carriers
• Electrons from the hydrogen atoms release energy down the electron transport chain between electron carriers
• The concentration of H+ ions in the intermembrane space is high forming an electrochemical gradient
• Protons diffuse down the electrochemical gradient through ATP synthase back into the matrix, this releases energy for ATP synthesis from ADP + Pi (chemiosmosis)
• In the matrix, H+ ions, electrons and oxygen combine to form water, oxygen is the final electron acceptor
• Without oxygen, FAD and NAD cant be reoxidised so will no longer be able to transport hydrogen, krebs cycle will stop, preventing oxidative phosphorylation
• Triglycerides can be used in respiration, glycerol (3C) is converted to triose phosphate to form pyruvate and fatty acid chains are split into 2C components for acetyl CoA formation
• Amino acids can be deaminated by the liver, remaining carbon atoms can be used in respiration at various stages depending on the size of the fragments
• Fatty acids and glycerol are used first when glucose stores deplete, then amino acids in cases of starvation
• Anaerobic respiration will stop at glycolysis, so a net gain of 2 ATP is made
• In alcoholic fermentation, pyruvate from glucose is decarboxylated, releasing 1 CO2, into ethanal then reduced into ethanol, releasing 1 NAD which is reused to produce pyruvate from triose phosphate
• In lactate fermentation, pyruvate is reduced to lactic acid, releasing 1 NAD to continue synthesis of pyruvate
• Buildup of lactic acid leads to cramping and pain, it is hydrolysed in the liver when oxygen becomes available
• Oxygen debt is how much oxygen is needed to completely break down lactic acid
• Respiration of 1 glucose produces 2 ATP and 2 NADH in glycolysis, 1 CO2 and 1 NADH in the link reaction, 2 CO2, 3 NADH, 1 ATP and 1 FADH in the krebs cycle and ATP and water in the electron transport chain