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1) How much energy is released when food burns in the body? 2) How is the caloric content of food determined?

1) How much energy is released when food burns in the body? 2) How is the caloric content of food determined?

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
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1) How much energy is released when food burns in the body? 2) How is the caloric content of food determined?
Transcribed Image Text:1) How much energy is released when food burns in the body? 2) How is the caloric content of food determined?
ntroduction Calorimetry and Combustion "Burning Food. Where are my carbs?" Burning food-what does that mean? As we digest and metabolize, the food we ate undergoes chemical reactions, and energy is released that our bodies use to fuel other processes. The ultimate products of our metabolism are carbon dioxide and water. These are the same products as they are for a combustion reaction, which occurs when organic molecules (e.g. fuels, carbohydrates, proteins, and fats) are burned in the presence of oxygen. Remember all combustion reactions are exothermic. Let's take a look at an example, the combustion of glucose (C6H1206): C6H1206(s) + 60₂(g) → 6C0₂(g) + 6H₂O(g) + heat (1) In our bodies, the chemical energy released by the combustion of food molecules is converted to different forms of energy: (1) heat to maintain our constant body temperature, (2) mechanical energy (to move our muscles), and (3) electrical energy (for nerve transmission). The total amount of energy released during our digestion is referred to as its calorie content and is expressed in units of nutritional Calories (Cal, uppercase C), not to be confused with the calorie (cal, lowercase c) you encounter in thermochemistry. One calorie (1 cal) is defined as the amount of heat required to raise the temperature of 1 gram of water by 1 °C. One nutritional Calorie (1 Cal) is defined as the amount of heat required to raise the temperature of 1 kilogram of water by 1 °C. Therefore, 1 Cal is equal to 1000 cal or 1 kcal. The calorie content of most prepared foods is listed on their nutritional information labels (Figure 18.1). Bomb calorimeters (Figure 18.2) allow us to determine the actual heat released by the combustion of food. They work in the same way as the coffee-cup calorimeter you used in the lab BUT with one big difference. In a coffee-cup calorimeter, the reaction takes place in water. In a bomb calorimeter, the reaction takes place in a sealed metal container (the bomb) surrounded by water inside an insulated container. Heat flow from the reaction crosses the walls of the bomb to the water. The temperature difference of the water is measured, just as it was for our coffee-cup calorimeter. Analysis of the heat flow is a bit more complex than it was for the coffee-cup calorimeter because the heat flow into the metal parts of the calorimeter must be taken into account. Nevertheless, the calculations are simple. All the heat released by the combustion is absorbed by the calorimeter. Thus, acombustion = -9calorimeter (2) Experiment 18
Transcribed Image Text:ntroduction Calorimetry and Combustion "Burning Food. Where are my carbs?" Burning food-what does that mean? As we digest and metabolize, the food we ate undergoes chemical reactions, and energy is released that our bodies use to fuel other processes. The ultimate products of our metabolism are carbon dioxide and water. These are the same products as they are for a combustion reaction, which occurs when organic molecules (e.g. fuels, carbohydrates, proteins, and fats) are burned in the presence of oxygen. Remember all combustion reactions are exothermic. Let's take a look at an example, the combustion of glucose (C6H1206): C6H1206(s) + 60₂(g) → 6C0₂(g) + 6H₂O(g) + heat (1) In our bodies, the chemical energy released by the combustion of food molecules is converted to different forms of energy: (1) heat to maintain our constant body temperature, (2) mechanical energy (to move our muscles), and (3) electrical energy (for nerve transmission). The total amount of energy released during our digestion is referred to as its calorie content and is expressed in units of nutritional Calories (Cal, uppercase C), not to be confused with the calorie (cal, lowercase c) you encounter in thermochemistry. One calorie (1 cal) is defined as the amount of heat required to raise the temperature of 1 gram of water by 1 °C. One nutritional Calorie (1 Cal) is defined as the amount of heat required to raise the temperature of 1 kilogram of water by 1 °C. Therefore, 1 Cal is equal to 1000 cal or 1 kcal. The calorie content of most prepared foods is listed on their nutritional information labels (Figure 18.1). Bomb calorimeters (Figure 18.2) allow us to determine the actual heat released by the combustion of food. They work in the same way as the coffee-cup calorimeter you used in the lab BUT with one big difference. In a coffee-cup calorimeter, the reaction takes place in water. In a bomb calorimeter, the reaction takes place in a sealed metal container (the bomb) surrounded by water inside an insulated container. Heat flow from the reaction crosses the walls of the bomb to the water. The temperature difference of the water is measured, just as it was for our coffee-cup calorimeter. Analysis of the heat flow is a bit more complex than it was for the coffee-cup calorimeter because the heat flow into the metal parts of the calorimeter must be taken into account. Nevertheless, the calculations are simple. All the heat released by the combustion is absorbed by the calorimeter. Thus, acombustion = -9calorimeter (2) Experiment 18
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