Question

1. The number of Calories in a substance can be estimated by burning it to completion in a bomb calorimeter. These can be called “chemistry Calories”. The number of Calories that are listed on a nutrition label are related to these, but differ from them. These “nutrition Calories” are an estimate of the energy available for making ATP. Here are some numbers for the amount of energy in a gram of various substances.

	Chemistry Calories/gram	Nutrition Calories/gram
Fat	11	9
Carbohydrate	5	4
Cholesterol	11	0

First explain why you think Cholesterol is “calorie-free” in a diet. Second explain why you think there are twice as many calories in a gram of fat than there are in a gram of sugar.

Answer 1

Cholesterol is a steroid, it is not used as a respiratory substrate like carbohydrate, fats and proteins (used as respiratory substrates at the time of starvation). Thus it does not give any energy and hence it is ''calorie free'' in diet.

Calories per gram of fat are twice the calories per gram of sugars, can be explained as:

The molecular weight of glucose is 180.

Therefore 180 gram of glucose will contain one mole (6.022 * 1023) of glucose molecules.

One glucose molecule produces about 38 ATP molecules on complete oxidation.

Thus 180 grams of glucose will produce:

38 * 6.022 * 1023 = 2.29 * 1025  molecules of ATP upon complete oxidation.

One gram will produce, 1.27 * 1023  molecules of ATP.

Now, molecular mass of palmitate, a fatty acid molecule present in fats is 256.

Thus 256 grams of palmitate Will contain one mole (6.022 * 1023) molecules of palmitate.

One molecule of palmitate on complete oxidation produces about 129 ATP moldcules.

Thus 256 grams will produce

129 * 6.022 * 1023  = 7.77 * 1025

One gram will produce about 6.02 * 1023 molecules of ATP.

Thus fats produce more number of ATP per gram than sugars