Mitochondria & ATP

1. Mitochondria & ATP • explain why the theoretical maximum yield of ATP per molecule of glucose is rarely, if ever, achieved in aerobic respiration; • explain, with the aid of diagrams and electron micrographs, how the structure of mitochondria enables them to carry out their functions;

2. Yield of ATP • We have seen that during the electron transport chain, most ATP is made (by substrate level phosphorylation) • Together with the ATP made during glycolysis and the Krebs cycle, the total yield of ATP molecules, per molecule of glucose respired, should be 30 • However, this is only a theoretical yield, in real situations the maximum yield (amount made) of ATP is not always possible • Look at the diagram showing the Electron Transport chain- try to think of reasons why the maximum yield of ATP is rarely achieved

4. Mitochondria: Structure and Function • First identified in animals in 1840, then in plants in 1900 • Have an inner and outer phospholipid membrane making up the envelope • Outer membrane smooth, inner membrane folded into cristae for a large surface area • Space between the inner and outer membrane known as the intermembrane space • The matrix is the middle bit (inside the inner membrane) it is gel like and made of proteins and lipids, looped mitochondrial DNA ribosomes and enzymes

6. Structure and Function • The matrix is where the link reaction and Krebs cycle take place- it contains: • Enzymes that catalyse these stages • NAD molecules • Oxaloacetate • Mitochondrial DNA that codes for mitochondrial proteins • Mitochondrial ribosomes (like bacterial ribosomes)

7. Outer Membrane • Phospholids with proteins forming channels allowing pyruvate through • Proteins that are enzymes are also contained here

8. Inner Membrane • Different lipid composition from outer membrane • Impermeable to most small ions including Hydrogen ions (protons) • Folded into cristae to give large surface area • Electron carriers and ATP synthase embedded into it

9. ATP Synthase • Large and protrude from inner membrane into matrix • Known as stalked particles • Allow protons through (H+)

10. Electron Carriers • Enzymes with non protein haem cofactors (containing iron) • The iron atoms become reduced Fe3+ to Fe2+ by accepting an electron (e-) then re-oxidised to Fe3+ by passing the electron onto the next carrier • Oxidoreductase enzymes are involved in the oxidation and reduction reactions • Electron carriers also have a coenzyme that pumps hydrogen ions from the matrix into the intermembrane space

11. Questions • Suggest how the structure of a mitochondrion from a skin cell would differ from that of a mitochondrion from the heart muscle tissue • Explain the following terms: proton motive force, oxidoreductase enzyme • It has been suggested that mitochondria are derived from prokaryotes. What features of their structure support this suggestion?

12. Questions • Suggest how the structure of a mitochondrion from a skin cell would differ from that of a mitochondrion from the heart muscle tissue mitochondria in a skin cell would be smaller and have fewer and shorter cristae as they are not as metabolically active as heart muscle cells • Explain the following terms: proton motive force, oxidoreductase enzyme The force generated by the flow of protons through ATP synthase channels down their concentration gradient. Enzyme that catalyses a reduction reaction that is coupled with an oxidation reaction • It has been suggested that mitochondria are derived from prokaryotes. What features of their structure support this suggestion? Their size, which is similar to bacteria, and they have circular DNA