Question

The first was the phosphoglycerol shuttle, the second was the malate-aspartate shuttle Briefly, describe why these shuttles are necessary and outline the advantages and disadvantages between these two shuttles with respect to ATP production.

Answer 1

cytosol Mitochondrial matrix Malate - Aspartate Shuttle Malate Malate - NAD+ NAD+ NADH NADH Advantage-To maximize ATP production, Cytosolic NADH should be transferred to mitochondrial matrix for ETC and cytosolic NAD should be regenerated for maintaining glycolytic flux and lactate conversion to Pyruvate. In heart MA shuttle (dominant than phosphoglycerol shuttle )maximize rate of transport of NADH into mitochondria upto 10 fold or more. They also act as a regulator for calcium homeostasis in cytosol and mitochondria Disadvantage- MA shuttle is incomplete in conditions like aerobic and ischemia Oxaloacetate Oxaloacetate Aspartate Aspartate

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  Cytosol Mitochondrial matrix Glycerolphosphate Shuttle Inner mitochondrial membrane glycerol 3 QH2 NADK phosphate -FADR Found primarily in muscles and brain. Advantage-Helps in rapid production of energy. Disadvantage- least efficient shuttle, less production of ATP compared to transport of electron to NAD+ as FAD acts as electron acceptor. That is 1.5 ATP instead of 2.5 ATP mGPD FADH2 NADH dihydroxyacetone phosphate