ATP and hydrogen carriers

when a hydrogen is released its added to a molecule called a hydrogen carrier for example NAD + H+ → reduced NAD

glycolysis

substrate-level phosphorylation:

  • molecule A is converted to molecule B and the energy released during this reaction is used to make a molecule of ATP

  • a hydrogen ion can be removed from a molecule = dehydrogenation/ oxidation , the hydrogen is transferred to a carrier

glycolysis takes place in the cytoplasm and does not require oxygen

  1. in the first stage glucose reacts with two molecules of ATP    

  2. each ATP molecules transfers one phosphate onto the glucose molecule = phosphorylation

  3. this activates the glucose and makes it more reactive = hexose bisphosphate

  4. hexose bisphosphate splits into two molecules of triose phosphate - a lysis reaction (splitting)

  5. inorganic phosphate ions from the cytoplasm reacts with each molecule of triose phosphate → triose bisphosphate

  6. each triose bisphosphate is converted into a molecule of pyruvate, reducing NAD and forming ATP

yield of glycolysis:

  • 2x ATP

  • 2x reduced NAD

  • 2x pyruvate

the link reaction

in the case of aerobic respiration this takes place in the mitochondria

pyruvate is transported into the mitochondrial matrix

pyruvate + coenzyme A → acetyl coenzyme A + carbon dioxide

NAD is reduced during this reaction to NADH - oxidation reaction

yield:

  • acetyl coenzyme A

  • carbon dioxide

  • NADH

the link reaction takes place twice for each molecule of glucose entering respiration

when carbon dioxide is removed from a molecule its called decarboxylation reaction

since there is a decarboxylation reaction and an oxidation reaction this is called oxidative decarboxylation

the krebs cycle

in the first stage:

  1. acetyl coenzyme a reacts with a 4 carbon molecule called oxaloacetate

  2. 2 carbons from acetyl coenzyme a move onto oxaloacetate forming a 6 carbon molecule called citrate

  3. at the same time coenzyme A is released and goes back to take part in the link reaction

second part:

  1. decarboxylation reaction releases one molecule of carbon dioxide from citrate and a dehydrogenation reaction produces one molecule of NADH forming a 5 carbon molecule

  2. the same happens again + one molecule of ATP is produced + two more dehydrogenation reactions producing one NADH and one FADH

yield of the krebs cycle:

  • ATP

  • 3X NADH

  • FADH

  • 2x carbon dioxide

oxidative phosphorylation

mitochondrial membrane

the first stage involves the electron transport chain:

  1. reduced NAD transfers two high-energy electrons to the first protein in the ETC

  2. the two electrons pass to the second protein

  3. as the electrons move down the ETC they lose energy - this energy is used to pump protons from the matrix into the intermembrane space

  4. 2 electrons combine with oxygen and two hydrogens in the matric to form water

  5. oxygen is the final electron acceptor

  6. the electrons from FADH enter the ETC in the middle rather than the start

  7. the concentration of protons is much greater in the intermembrane space than the matrix

  8. ATP synthase contains an ion channel in the centre - protons diffuse down the gradient through the ion channel into the matrix

  9. this movement of ions is used by ATP synthase to generate ATP from ADP and Pi = chemiosmosis

anaerobic respiration

in animals:

there is not enough NAD for glycolysis to take place, so the cell uses the reduced NAD produced by glycolysis to reduce the pyruvate to lactate/lactic acid:

by reducing pyruvate to lactate the cell can keep glycolysis functioning

  • the reaction is catalysed the enzyme lactate dehydrogenase

  • takes place entirely in the cytoplasm

  • occurs in muscles during intense exercise and transported to the liver where its converted to glucose

in plants: