The Cori cycle is viewed as 33% efficient, in that 33% of the energy mobilized i

Question

The Cori cycle is viewed as 33% efficient, in that 33% of the energy mobilized in the liver is delivered for use in the destination tissue (quite often muscle), and the rest utilized as the 'cost of this transport. (This low efficiency is one reason we have evolved to perceive a characteristic metabolite of its operation, lactic acid, as sometimes mildly uncomfortable, in cramping or 'the burn' after intense exercise turns muscle anaerobic.) The other pathway we have studied so far that transports things between tissues is the ketone bodies pathway. Here too, we may characterize its efficiency in terms of how much of the total energy is actually delivered. Consider a given amount of fat mobilized by the ketone bodies pathway, and answer the following questions. For purposes of this, consider all energy converted to all the way to ATP by other appropriate pathways of a mammal. a. What percentage of the fat's energy is delivered to the destination tissue? To do this you need to figure out i. How much ATP a given fat could potentially produce under 'normal conditions (use 1 g or 1 mole or whatever you want of whichever fat you want...) How much ATP is produced in the destination tissue. i.. i What the energy value is of this ATP in each case. Use physiological values of AG for ATP based on the table to the right. Then calculate the percentage delivered. iv.

Explanation / Answer

When your body runs out of glucose, it turns to fat for energy, which has 9 calories in every gram. This is a little more than double the amount in carbohydrates. Converting fat into energy takes longer than it does to convert glucose into energy, because fat must be first be broken down into its two component parts: fatty acid and glycerol. Each part follows a separate pathway to ultimately become available as energy. One common saturated fat, palmitic acid, makes 130 molecules of ATP for each molecule of fat.

I g of palmitic acid produces 0.41 molecules of ATP

the glycolysis part of the cycle produces 2 ATP molecules at a cost of 6 ATP molecules consumed in the gluconeogenesis part. Each iteration of the cycle must be maintained by a net consumption of 4 ATP

So 33% efficiency is equal to 33*4/100=1.32

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