Link Reaction/Pyruvate Oxidation/Krebs/Respiratory Chain/Chemiosmosis

Where does this take place

• in the mitochondrial matrix

• pyruvate diffuses in from cytoplasm into mitochondrial matrix

Enzyme involved in catalyzing this reaction

pyruvate dehydrogenase enzyme complex

Brief outline of link reaction

pyruvate + coA + nad+ → Nadh +H+ Co2, and acetyl coA

more detailed explanation 

1. Pyruvate undergoes decarboxylation to produce acetyl + co2

2. acetyl reacts with coA to form Acetyl CoA

3. in the decarboxylation of pyruvate high energy electrons are released - these are taken up by NAD+ 

Krebs Cycle - where does it take place 

• in the mitochondrial matrix 

Detailed Krebs Cycle explanation

1. Acetyl CoA produced from Link reaction reacts with oxaloacetate to form citrate

2. Citrate then undergoes decarboxylation to form co2 and a 5C molecule

3. in the process nad+ → NADH+ +H+ is produced

4. more dehydrogenation reactions occur producing another co2 molecule, ATP, 2 more nadh+ +h+ molecules and 1 molecule of FADH2

5. oxaloacetate is then regenerated

how is the atp molecule generate in krebs

• due to decarboxylation and oxidation of intermediates energy is released

• this can be used to synthesize 1atp for each turn of the cycle

• atp is formed by substrate level phosphorylation

how are these fadh2 and nadh + H+ produced

• this is because in the krebs cycle intermediates are oxidized and these hydrogens then go to the FAD and Nad+

at the end of krebs….

1. all hydrogens of glucose are on Nad+ and FAD

2. all carbons originally in glucose have also been lost as Co2

2CO2, 1 ATP, 3NADH+ +H+ and 1 FADH2 are generated.

Describe the respiratory chain/electron transport chain

• the electron carriers move to the inner membrane of the mitochondrion on the cristae

• donate their electrons to the cytochromes in the electron transport chain

• electrons flow from one cytochrome to the next and a series of redox reactions take place

• enter via protein complex 1 (nadh +h+)

• fadh2 electrons enter via complex 2

• both are transferred to coenzyme q, then to complex 3, cytochrome c then to complex 4 then to oxygen

• oxygen is the final electron acceptor

  • O2 + 4h+ 4e → 2h20 + energy

  • clears out electrons from etc,

• the energy released as electrons move down the electron transport chain is used to synthesize atp

• released in small bundles to avoid damaging the cell

cytochromes

• protein complexes in the cell membrane

• have a brownish color due to the ion

• have a prosthetic group similar to haem in haemoglobin but binds to e- instead of o2

define chemiosmosis 

• movement of ions across a membrane down an electrochemical gradient

Chemiosmotic Synthesis of ATP

• flow of electrons through etc generates energy

• this energy allows cytochromes to pump h+ from the matrix to the intermembrane compartment against conc gradient

• H+ concentration is now steep.

• h+ cant cross through hydrophobic layer so it must pass through a proton channel called atp synthase - this couples proton movement to atp generation from adp + pi

• this provides 32/34 molecules of atp

• atp synthesized diffuses out of matrix to cells, and adp diffuses in from cytoplasm

• nadh +h + = 3 atp molecules

• fadh2 = 2 atp molecules made

Why is oxygen so important in the electron transport chain

• beacuse without oxygen to accept electrons, the electrons would pile up in the chain

• the cytochromes would be full of electrons and cant accept anymore

• no more movement of electrons = no more energy

• no more h+ pumped

• no more atp synthesized