B12 respiration

• glycolysis is the process by which glucose is split into pyruvate
• glycolysis is the initial stage of aerobic respiration and anaerobic respiration
• glycolysis has the following stages:

  • phosphorylation of glucose
  • splitting of glucose phosphate
  • oxidation of triose phosphate
  • production of ATP
• the first stage of glycolysis is the phosphorylation of glucose to glucose phosphate, making it more reactive, using phosphate molecules from ATP hydrolysis
• the second stage of glycolysis is the splitting of 1 glucose phosphate into 2 triose phosphate molecules
• glucose is a 6 carbon molecule
• glucose phosphate is a 6 carbon molecule
• triose phosphate is a 3 carbon molecule
• the third stage of glycolysis is oxidation of triose phosphate, hydrogen is removed from each and transferred to NAD which reduces it to NADH
• the fourth stage of glycolysis is the production of ATP, enzyme-controlled reactions convert triose phosphate into pyruvate, producing 2 molecules of ATP from condensation
• glycolysis produces ATP, NADH and pyruvate
• the overall yield of glycolysis is:

  • 2 molecules of ATP
  • 2 molecules of NADH
  • 2 molecules of pyruvate
• the link reaction converts pyruvate to acetyl coenzyme A
• the link reaction contains a series of steps:

  • 2 molecules of pyruvate are actively transported into the mitochondria
  • pyruvate is oxidised to acetate, by losing 1 carbon dioxide and 2 hydrogens
  • hydrogen reduces NAD to form NADH
  • acetate combines with coenzyme A to produce acetyl coenzyme A
• the overall equation for the link reaction is:

  pyruvate + NAD + CoA -> acetyl CoA + NADH + carbon dioxide
• the Krebs cycle is a series of redox reactions that takes place in the mitochondria
• the Krebs cycle has the following steps:

  • acetyl coenzyme A combines acetate with a 4 carbon molecule to make a 6 carbon molecule
  • the 6 carbon molecule loses 2 carbon dioxide and 2 hydrogens through a series of reactions, releasing 1 ATP, becoming a 4 carbon molecule
  • the H reduces NAD and FAD to NADH and FADH
  • the 4 carbon molecule can repeat the cycle
• the overall yield of the link reaction and Krebs cycle, from one molecule of pyruvate, is:

  • reduced NAD and FAD
  • 1 molecule of ATP
  • 3 molecules of carbon dioxide
• FADH and NADH are important products because they have the potential to provide energy to produce ATP molecules by oxidative phosphorylation
• oxidative phosphorylation is the movement of electrons down the electron transfer chain
• the first stage of oxidative phosphorylation is: NADH and FADH donate the electrons of the H to the first electron acceptor, and release the H+ as protons
• the second stage of oxidative phosphorylation is: electrons pass down the chain through a series of redox reactions
• the third stage of oxidative phosphorylation is: as electrons flow, they release energy, used to pump protons across the inner-mitochondrial membrane into inter-membranal space
• the fourth stage of oxidative phosphorylation is: protons build up, creating a concentration gradient, so diffuse back into the matrix through ATP synthase channels in the membrane
• the fifth stage of oxidative phosphorylation is: at the end of the chain, electrons combine with protons and oxygen to form water, so oxygen is the final electron acceptor
• in the absence of oxygen, the Krebs cycle and electron transfer chain cannot continue because all of the NAD and FAD is reduced, so unable to take up the hydrogen ions produced, which changes the pH and denatures the enzymes
• in the absence of oxygen, the only way left to produce ATP is glycolysis, but it produces pyruvate and hydrogen which need to be constantly removed
• in the absence of oxygen, in plants and microorganisms, the pyruvate molecule loses a carbon dioxide and accepts hydrogen from NADH to produce a molecule of ethanol
• the overall equation for anaerobic respiration in plants and microorganisms is:

  pyruvate + NADH -> ethanol + carbon dioxide + oxidised NAD
• in the absence of oxygen, in animals, the pyruvate molecule takes up two hydrogens from NADH to form lactate
• the overall equation for anaerobic respiration in animals is:

  pyruvate + NADH -> lactate + oxidised NAD