Respiration

• Glycolysis

  First process of both aerobic and anaerobic respiration occurring in the cytoplasm. Glucose is phosphorylated to produce 2 molecules of pyruvate, 2 molecules of NADH, and a net production of 2 molecules of ATP
• Link reaction

  Each pyruvate is converted to acetyl which binds to coenzyme A. NAD is reduced to NADH and CO2 is produced as pyruvate is decarboxylated
• Respiration

  Aerobic respiration releases carbon dioxide as a waste product and reunites hydrogen with oxygen to release energy. Anaerobic respiration occurs without oxygen. It is a multi-step process with each step controlled by a specific intracellular enzyme
• The respiratory quotient (RQ) can be measured to determine which respiratory substrate is being used and to determine if the organism is undergoing anaerobic respiration. Different respiratory substrates have different RQ values e.g. carbohydrates have a value of 1.0, lipids – 0.8 and proteins 0.9
• Anaerobic Respiration occurs when the concentration of oxygen is low. ATP production still needs to happen but this can’t be done by oxidative phosphorylation due to the lack of oxygen to act as the final electron acceptor. In mammals, pyruvate is converted to lactate. Pyruvate acts as the hydrogen acceptor to enable NADH to be reoxidised to NAD which can then be used to continue the reactions in glycolysis. Lactate can then be converted back to pyruvate in the liver cells when the oxygen levels rise again. Yeast and plants use alcoholic fermentation to enable glycolysis to continue. In this process Pyruvate is decarboxylated to EthanAl which in turn is reduced to ethanOl reoxidising NAD in the process. So ethanAl is the hydrogen acceptor. The first step in this process produces CO2 and therefore this is an irreversible reaction
• Conversion of pyruvate to acetyl

  Each pyruvate is converted to acetyl which binds to coenzyme A. In the process NAD is reduced to NADH and CO2 is produced as pyruvate is decarboxylated
• Respiratory substrates include carbohydrates, lipids, and proteins which release varying amounts of energy, depending on the number of hydrogens in the structure which are oxidised to water. The number of hydrogens is greater in fatty acids than carbohydrates
• Oxidative phosphorylation

  ATP is synthesised in the electron transport chain in mitochondria. This process generates the majority of ATP in aerobic respiration. It occurs as follows: Reduced coenzymes (NADH and FADH) carry hydrogen ions and electrons to the electron transport chain which occurs on the inner mitochondrial membrane. Electrons are carried from one electron carrier to another in a series of redox reactions. The energy provided by the electrons to the electron carriers is used to move hydrogen ions across the inner membrane into the intermembrane space. ATP is produced on stalked particle using ATP synthase. Hydrogen atoms are produced from hydrogen ions and electrons, then combined with oxygen to produce water. Oxygen acts as the final electron acceptor. There is a theoretical yield of 38 ATP molecules per glucose molecule but in real life, this is rarely achieved due to the inner mitochondrial membrane being ‘leaky’ to H+ therefore not all H+ move through the ATPase. The pyruvate made during glycolysis in cytoplasm needs moving into the matrix by active transport and so this uses ATP
• Delivery of Acetyl to the Krebs cycle


  Co-enzyme A delivers Acetyl to the Krebs cycle where glucose is oxidised and carbon dioxide, ATP, reduced NAD, and reduced FAD are produced. Each glucose molecule causes the cycle to turn twice so per glucose, we produce 4CO2, 4NADH, 2FADH, and 2ATP molecules in the Krebs cycle. The ATP molecules produced by the Kreb’s cycle are done so by substrate level phosphorylation