Respiration

• Aerobic respiration is a process that occurs in all living organisms and involves catabolic, enzyme-controlled reactions inside cells to provide energy.
• Energy rich respiratory substrates, such as glucose or fatty acids, are broken down to release energy.
• During aerobic respiration, high-energy bonds (C-C, C-H and C-OH) are broken and lower-energy bonds are formed.
• 2 reduced FAD from Kreb’s cycle release 4 ATP.
• 2 reduced NAD from the link reaction release 6 ATP.
• The net yield of ATP from substrate level phosphorylation is 2 from glycolysis, 2 from Kreb’s.
• 2 reduced NAD from glycolysis produce 6 ATP in ECT.
• 6 reduced NAD from Kreb’s cycle release 18 ATP.
• The excess energy released in aerobic respiration is used to phosphorylate ADP to form ATP or is released as heat energy.
• Glycolysis, a process that occurs in the cytoplasm, involves the phosphorylation of glucose using 2 ATP into hexose phosphate.
• The hexose phosphate produced in glycolysis splits into two triose phosphate molecules.
• The oxidation of these 2 triose phosphate molecules yield 2 ATP each by substrate level phosphorylation.
• Overall glycolysis has a net gain of 2 ATP.
• Dehydrogenation releases 2 Hydrogen that are picked up by NAD.
• The 2 pyruvate produced in glycolysis diffuse into the mitochondria.
• In the link reaction, which occurs in the mitochondrial matrix, oxidative decarboxylation of pyruvate catalysed by decarboxylase releases carbon dioxide.
• Respiratory substrates other than glucose include Lipids, Proteins, and Sugars.
• Each reduced NAD utilises all 3 proton pumps, releasing 3ATP.
• Glycerol is converted into triose phosphate for use in glycolysis.
• Reduced NAD and reduced FAD, from glycolysis and Kreb’s cycle, deliver pairs of hydrogen atoms to the ETC.
• Each reduced FAD utilises only 2 proton pumps, releasing 2 ATP.
• Amino acids are deaminated in the liver into ammonia and keto acids, one of which (pyruvate) is used in the link reaction while the others are fed into the Krebs cycle as intermediates.
• Oxygen is the final acceptor in the electron transfer chain and is reduced to water.
• Fatty acids are split into 2C acetate fragments which feed into the Krebs cycle as acetyl CoA.
• For each molecule of glucose, the link reaction and Kreb’s cycle happen twice because each molecule of glucose leads to the formation of two triose phosphate in glycolysis.
• Reduced NAD and reduced FAD are oxidised, delivering protons (H+) and high-energy electrons (e-) to proton pumps on the inner mitochondrial membrane.
• Dehydrogenation catalysed by dehydrogenase releases pairs of hydrogen atoms converting NAD to reduced NAD.
• The addition of coenzyme A forms acetyl CoA (2C) which enters the Krebs cycle.
• In the Krebs cycle, the acetate from acetyl CoA combines with a 4C compound to form a 6C compound.
• Decarboxylation forms a 5C compound and dehydrogenation occurs reducing NAD.
• Decarboxylation forms a 4C compound and dehydrogenation to reduce NAD.
• There is also substrate level phosphorylation giving 1 ATP.
• Dehydrogenation forming reduced NAD and FAD.
• The electron transport chain, which occurs on the inner mitochondrial membrane, is the final step in aerobic respiration.
• Anaerobic respiration occurs in the absence of oxygen.
• Without oxygen to act as the final electron acceptor, biochemical reactions inside the mitochondria grind to a halt as any reduced NAD and FAD cannot be reoxidised to pick up more hydrogen.
• A mechanism in glycolysis allows reduced NAD to transfer hydrogen to pyruvate, allowing NAD to accept hydrogen from glucose.
• Glycolysis can proceed giving a net yield of 2 ATP for each glucose entering the reaction.
• In the first step of glycolysis, triose phosphate is converted to pyruvate with the release of ATP and reduction of NAD.
• Reduced NAD reduces the pyruvate, forming lactate.