Electron Transport Chain Lecture 9 BIOL2020 PDF

Electron transport chain Lecture 9 BIOL2020 Amino acids, sugars, and lipids feed into the TCA cycle Glucose Fatty acids Everything from this image is important Glycolysis Glucose→ 2 Pyruvate + 2 NADH +2 ATP Oxidation of Glucose liberates energy Cytoplasm Pyruvate Dehydrogenase (PDH) Pyruvate →...

Electron transport chain Lecture 9 BIOL2020 Amino acids, sugars, and lipids feed into the TCA cycle Glucose Fatty acids Everything from this image is important Glycolysis Glucose→ 2 Pyruvate + 2 NADH +2 ATP Oxidation of Glucose liberates energy Cytoplasm Pyruvate Dehydrogenase (PDH) Pyruvate → Acetyl-CoA +NADH TCA cycle Acetyl-CoA → CO2 + 3 NADH + FADH2 + ATP Also makes AAs Regenerates (cataplerotic and anaplerotic) beta oxidation makes Acetyl-CoA from fatty acids The TCA products are ● CO2 ● NADH ● FADH2 ● ATP The Electron Transport Chain The goal of the electron transport chain is to use NADH and FADH2 to concentrate H+ protons in the intermembrane space The energy is provided by the oxidation of NADH into NAD+ Remember ATPases? Instead of ATP, the ETC uses electrons from NADH or FADH2 The hydride ion is removed from NADH (to regenerate NAD+) and is converted into a proton and two electrons (H-→ H+ + 2e -) The ETC converts NADH reduction into a gradient of protons ● ● The electrons start with very high energy and gradually lose it as they pass along the chain. electrons pass sequentially from one complex to another until they are finally transferred to oxygen The ETC requires the close association of the electron carriers with protein molecules.The electron carriers are prosthetic groups Iron-sulfur clusters ● ● Flavin mononucleotide (comes from Vitamin B2) Prosthetic groups are large non-protein molecules embedded in the protein Complicated chemical structures not possible with amino acids Example: heme is the prosthetic group in hemoglobin and is is necessary for oxygen binding Complex I receives 2 electrons from NADH and passed them to CoQ. The energy is used to pump 4 H+ Coenzyme Q (CoQ) is a lipid-like carrier (aka ubiquinone) CoQ CoQH2 Complex II receives 2 electrons from succinate passing them directly to FADH2 and then into to CoQ. Does not pump H+ Is also called Succinate dehydrogenase and is a TCA cycle Complex III receives 2 electrons from CoQ and passed them to Cytochrome C. The energy is used to pump 4 H+ Cytochrome c is a small protein that serves as carrier of electrons Heme ● ● ● CytC moves Electrons from complex 3 to 4 CytC is a small protein with a Heme cofactor Heme is the electron carrier Complex IV receives 2 electrons from Cytochrome C and passed them to Oxygen, which is reduced to water. The energy is used to pump 2 H+ Electrons move in a single direction because Redox centers (electron carriers) are organized from low to high affinity NADH gives 2 electrons Redox centers Coenzyme Q Nice summary and animation here: https://www.youtube.com/watch?v=LQmTKxI4Wn4 ● ● ● NADH → 1 → 3 → 4 → O2 FADH2 → 2 → 3 → 4 → O2 The redox centers and the H+ pumps are separated in complex Electron Transport Complex I Matrix Tandem Proton Pumping Intermembrane space Structural changes in Complex I direct H+ to move through translocation half-channels Intermembrane space ● half-channels are formed by conserved polar residues and polar cavities containing water molecules Matrix Structural changes in Complex I direct H+ to move through translocation half-channels The ETC forms supramolecular assemblies or supercomplexes ● Meaning that the complexes are clustered together Finally, the H+ flow back powering the synthesis of ATP The power source for the ATP synthase is a difference in the concentration of H+ on opposite sides of the inner mitochondrial membrane. Protons move through here → H + ADP + Pi + squeezing force = ATP ATP synthesis happens here → https://www.youtube.com/watch?v=nmoLoiFakxY Summary TCA cycle Makes NADH and FADH2 Oxaloacetate is the start/end Other metabolites reach the cycle ETC Prosthetic groups do the complicated chemistry Organized redox centers direct electrons The electron force is used to pump H+ into the intermembrane space ATP synthase Converts H+ gradient into ATP