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Respiration

Respiration

 

  • ATP is formed due to the phosphorylation of ADP 

  • Uses the process of dehydrogenation, decarboxylation, phosphorylation (oxidative for the ETC and substrate level for glycolysis and krebs)

  • Coenzymes function as carrying molecules and carry 

  • Oxidise glucose by dehydrogenation 

  • Eliminate the carbon and the oxygen which leads to decarboxylase 

  • Hydrogenation leads to reduced coenzymes benign formed 

  • These coenzymes must be oxidised as otherwise respiration would stop 

  • So in final stage hydrogen is release 

  • Energy released leads to the pumping of H+ ions which form s a protein gradient this enables chemiosmosis 

  • Oxygen is vital to enable the co-enzymes to be reoxidised and for respiration to continue 

  • Can calculate a respiratory quotient or RQ which enables us to understand how much oxygen is needed for that respiratory substrate 

  • For glucose = 1

  • Glycolysis:

    • 2 molecules of ATP that are used to split the glucose molecules to form hexose bisphosphate (phosphorylation  

    • This is split into triose phosphate 

    • through addition of inorganic phosphate triose bisphosphate is formed 

    • Phosphates are removed and the reduced NAD is formed to give 2 pyrubate (dehydrogenation) 

  • If there is no oxygen the pyruvate will be anaerobically repaired either through lactate pathway or through fermentation 

  • Link Reaction:

    •  

  • Kreb Cycle:

    • Pyruvic Acid is converted to acetyl coenzyme A 

    • This is converted to citric acid 

    • This is then acted on to remove the CO2 and a NAD+ is reduced as hydrogen is removed 

    • A further NAD is reduced and CO2 removed 

    • ADP and an inorganic phosphate mol

    • Produced:

    • 4 co2 

    • 6 reduced NAD 

    • 2 reduced FAD 

  • Oxidative Phosphorylation:

    • Reduced NAD is oxidised to produced H+ and 2 e- 

    • These e- can then be passed into complex I and move through an electron transport chain releasing energy with each movement and this energy is used to pump H+ ions out and build up a proton gradient

    • This proton gradient that form causes the protons to diffuse through he ATP synthase complex from high to low electrochemical potential creating ATP 

    • This is chemiosmosis 

    • THe electrons react with the water molecule and 2 H+ to form H2O and so oxygen is the final electron acceptor 

If an RQ value is very high then it would be anaerobic respiration but generally for anything other than oxygen will be less than1  

 

Evidence for chemiosmosis would be very low pH 

Focus:

Different types of phosphorylation 

Role of coenzymes 

COmparison of Krebs and Calvin 

 

Comparison of carbon and nitrogen cycle

LOOK THROUGH WHAT IS GOOD FOR COMPARISON 


 

Make sure to learn the importance of coenzymes in respiration

 

Glycolysis - Occurs in cytoplasm 

  1. Phosphorylation - 2 steps converts glucose to hexose bisphosphate (6C & 2P) [requires 2 ATP]

  2. Splitting of Hexose Bisphosphate into 2 triose phosphate molecules 

  3. Oxidation of TP to Pyruvate (involves 2 x NAD converted to reduced NAD and 4 ADP converted to ATP)

  • Products: 2 x ATP (net as 4 produced but 2 used earlier), produces 2 x reduced NAD, 2 x pyruvate

  • In anaerobic conditions only this pathway will occur and pyruvate will be converted to either lactate or ethanol oxidising the reduced NAD to NAD so that glycolysis can occur again

 

Link Reaction: - Occurs in the Mitochondrial matrix

  • Pyruvate transported by a symport pyruvate-H+ pump into the matrix 

  • Catalysed by pyruvate dehydrogenase 

  • Pyruvate is dehydrogenated and decarboxylated 

  • Carboxyl group is removed and some hydrogens which produces an acetyl group 

  • This combines with coenzyme A to form Acetyl coenzyme A

  • This required NAD which become reduced NAD

 

Krebs Cycle: Occurs in the mitochondrial matrix 

  • Acetyl group of Acetyl CoA is released and combines with a four carbon compound, oxaloacetate, to form citrate which is a 6 carbon compound 

  • Citrate is decarboxylated and dehydrogenated to produce a 5 carbon compound as well as a molecule of CO2 and a molecule of reduced NAD

  • This 5 carbon compound is further decarboxylated and dehydrogenated forming a four carbon compound as well as the same by-products 

  • Substrate level phosphorylation occurs producing an ATP molecule as the 4 carbon compound combines temporarily with coenzyme A 

  • 4 carbon compound if further dehydrogenated produced reduced FAD and a further 4 carbon compound 

  • Isomerase rearranges the atoms in the 4 carbon compound which leads to a further dehydrogenation and regeneration of oxaloacetate  so the cycle confines 

  • Essentially Acetyl Co A → Citrate → 5C → 4C → 4C –4C → Oxaloacetate 

  • Essentially produces: 2 molecules of ATP, 4 molecules of CO2, 2 molecules of rFAD and 6 molecules of rNAD 

 

Oxidative Phosphorylation: Mitochondrial membrane (inner)

  • Produces 28 ATP per cycle 

  • Involves electron transport chains (ETCs) in the inner membranes or cristae which generate ATP ina process called chemiosmosis

  • Reduced NAD/FAD is/are reoxidised when they deliver the Hydrogen to the ETC

  • These hydrogen ions are split into protons and electrons and the protons go into solution in the matrix 

  • The electrons are passed along an electron transport chain of electron transport proteins. These have an iron ion at their core which can be reduced in gaining an electron to Fe2+ 

  • This ion can theme donate the electron to the next Fe3+ ion in the ETC becoming reoxidised itself and ready to accept another electron 

  • The energy used in the passing of the electrons is used to pump protons across the inner mitochondrial membrane to the intermembrane space 

  • As protons accumulate in the intermembrane space a proton gradient forms across the membrane 

  • The proton gradient creates a chemiosmotic pressure known as the proton motive force which is used to make energy 

  • The protons cannot easily diffuse through the membrane as the outer membrane has low permeability, as a result the protons must diffuse through a proton channel. This protein channel is associated with ATP synthase. 

  • As the hydrogen ions flow down the concentration and electrochemical gradient they cause a conformational change in the ATP synthase that allows ADP and inorganic phosphate to combine to form ATP 

  • Oxygen acts as the final electron acceptor and combines with the electrons from the electron transport chain and with protons which have diffused through the membrane and generated ATP to form water (4H+ 4e- + O2 → 2H2O)

 

Anaerobic:

  • Either ethanol fermentation of lactate fermentation pathway for Eukaryotic 

  • Ethanol: 

    • Pyruvate is decarboxylated to ethanal by pyruvate decarboxylase 

    • Ethanal dehydrogenase is converted to ethanol with the use of H from reduced NAD thus regenerating NAD and so glycolysis continues

  • Lactate:

    • Pyruvate is converted to lactate using lactate dehydrogenase and the hydrogen from reduced NAD which is oxidised to NAD

    • Glycolysis continues 

    • Lactate is then taken to the Liver and when more oxygen is available may be converted to pyruvate to enter the Link reaction and the rest of respiration or may be converted to glucose and glycogen (stored) 

    • If lactate were not removed the pH of the tissue lowers and the action of enzymes will be inhibited. 

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