Respiration

• Respiration


  Fundamental to life
• Respiration is fundamental to life
• Respiration happens inside the body, inside cells, in the cytoplasm (glycolysis) and in mitochondria (link reaction, TCA cycle, oxidative phosphorylation)
• Metabolism

  Catabolism - Breaking down of molecules, Anabolism - Building of molecules
• Metabolic substrates

  • Carbohydrate
  • Protein
  • Fat
• Metabolic products

  • Glucose
  • Amino acid
  • Glycerol/Fatty acids
• Catabolic reactions

  1. Acetyl CoA

  2. TCA cycle

  3. NADH/FADH2

  4. Oxidative phosphorylation

  5. O2

  6. H2O

  7. ATP
• ATP


  Energy carrying molecule, required for anabolic reactions, cellular work, active transport, cell movement
• An average heart weighs 300g and requires a large amount of ATP every day
• Respiration happens in all eukaryotes, not just in plants
• ATP

  Adenosine 5'-Triphosphate, most important and versatile of the activated carriers in cells, a ribonucleotide, terminal group is frequently split off by hydrolysis
• NADH, FADH2

  Important energy carrying molecules in respiration, can be regarded as electron donors/acceptors
• Glycolysis

  Splitting glucose apart, yields a small amount of ATP, occurs in the cytoplasm, does not require oxygen, generates pyruvate and lactate
• Glycolysis

  • Costs ATP, generates ATP, each phase consists of multiple enzymatic steps
• Glycolysis steps

  1. Phosphorylation of hexose (glucose) to hexose bisphosphate (fructose bisphosphate)

  2. Splitting of hexose (fructose) bisphosphate into two triose phosphate (glyceraldehyde phosphate) molecules

  3. Oxidation to pyruvate, producing a small yield of ATP and reduced NAD
• For a single molecule of glucose, glycolysis produces 2 ATP, 2 NADH, and 2 pyruvate
• Pyruvate is actively transported into the mitochondria (aerobic respiration)
• Glucose phosphate

  Glucose 'trapped' inside the cell - cannot be transported back out
• Fructose phosphate

  Isomerised from glucose phosphate, raises the energy level (i.e. makes it more reactive)
• Step 1 - phosphorylation

  1. Glucose -> Glucose phosphate -> Fructose phosphate

  2. ATP -> ADP
• Step 1 - phosphorylation

  1. Fructose phosphate -> Fructose bisphosphate

  2. ATP -> ADP
• Fructose bisphosphate

  Hexose split into 2 glyceraldehyde phosphate (triose) molecules
• Step 2 - splitting hexose

  1. Fructose bisphosphate -> Glyceraldehyde phosphate

  2. Glyceraldehyde phosphate
• Step 3 - oxidation to pyruvate

  1. Glyceraldehyde phosphate oxidised anaerobically, NAD+ reduced, bisphosphoglycerate formed, further 4 enzyme steps to pyruvate

  2. 2 ATP produced by substrate level phosphorylation
• For a single molecule of glucose (hexose), 2 ATP, 2 NADH, 2 pyruvate (triose) are produced
• Pyruvate transport

  Actively transported into the mitochondria (aerobic), remains in the cytoplasm under anaerobic conditions
• Link reaction

  1. Pyruvate cannot directly enter the TCA cycle, conversion to acetate, linked to coenzyme A, allows acetyl CoA to enter the TCA cycle

  2. Catalysed by pyruvate decarboxylase (removal of carboxyl group) and pyruvate dehydrogenase (removal of protons, accepted by NAD+)
• For each glucose molecule entering glycolysis, 2 pyruvate molecules are generated (i.e. 2 link reactions occur)
• TCA / citric acid / krebs cycle

  First sequenced by Hans Krebs in 1937, acetyl CoA from link reaction combines with oxaloacetate to form citrate, series of decarboxylation and dehydrogenation reactions to reform oxaloacetate
• For a single molecule of pyruvate (3C), 1 ATP, 4 NADH, 1 FADH2, 3 CO2 are produced in the link reaction and TCA cycle
• For a single molecule of glucose (6C), 2 ATP, 8 NADH, 2 FADH2, 6 CO2 are produced in the link reaction and TCA cycle
• Electron transport chain (ETC)

  Electrons are passed from one member of the transport chain to another in a series of redox reactions, produces a proton gradient, used for chemiosmosis and oxidative phosphorylation
• Electron transport chain - step 1

  Supply of electrons from NADH and FADH2, electrons passed down the chain of proteins, releasing energy to pump protons from the matrix into the intermembrane space
• Electron transport chain - step 2

  Electrons transferred to molecular oxygen at the end of the chain, oxygen splits and reacts with H+ to form water
• Electron transport chain - step 3

  Protons flow back down the gradient into the matrix through ATP synthase, driving the enzyme to synthesize ATP (chemiosmosis)
• Each NADH can in theory provide 2.6 molecules of ATP by oxidative phosphorylation
• 2 FADH2 can each produce 2 molecules of ATP
• Total ATP yield per glucose molecule is the sum of 4 ATP from substrate level phosphorylation and the ATP from oxidative phosphorylation
• Oxidative phosphorylation not possible in anaerobic conditions, significantly less energy produced
• ATP yield is reduced by energy required for active transport into/out of mitochondria, and dissipation of the proton gradient