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;

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

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

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)

Outer Membrane

• Phospholids with proteins forming channels allowing pyruvate through

• Proteins that are enzymes are also contained here

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

ATP Synthase

• Large and protrude from inner membrane into matrix

• Known as stalked particles• Allow protons through (H+)

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

Questions

1. Suggest how the structure of a mitochondrion from a skin cell would differ from that of a mitochondrion from the heart muscle tissue

2. Explain the following terms: proton motive force, oxidoreductase enzyme

3. It has been suggested that mitochondria are derived from prokaryotes. What features of their structure support this suggestion?

Questions1. 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

2. 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

3. 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