Energy and Nutrition, Blog from Class on January 30, 2015
Points from the Lecture on Energy. I presented some aspects of energy in nutrition but stopped because we will discuss this again in material for exam 2. However, I wish to give you the outline of the rest of the story now.
- Calories — This is a unit of measure for the energy form called heat. The nutrition calorie is, in fact, the kilocalorie (Kcal). The average intake in women is about about 2200 Kcal per day, and the average intake in men is about 2800 Kcal per day. Throughout the course the abbreviation Kcal is used. However, when I do use the full name calorie, I am referring to the Kcal. For those who study chemistry, the chemistry calorie is the one that can raise the temperature of 1 cubic centimeter of water one degree centigrade. Consuming 2000 chemistry calories would be equivalent to consuming 2 Kcal – this would not get you very far!
- A Kcal is a Kcal is a Kcal. The energy that is present within the major energy macronutrients is not changed when the macronutrients enter a human’s mouth. Anyone who states that, after food is consumed, the energy of one type of macronutrient is not utilized compared to the energy in another type of macronutrient is ignoring 100 years of the research that was performed on energy utilization in animals. Furthermore, they would have to violate several major Laws of Physics.
- But where is the energy?To find out where energy comes from in food, it is best to investigate some of the properties of fat.Fat is structurally similar to gasoline, and we know that gasoline is a source of energy as it can be used to propel very heavy automobiles around town. Both fat and gasoline are long chains of carbons with hydrogens attached (also known as hydrocarbons). Fatty acids have a characteristic carboxyl group at one end of the molecule, that gives it soap-like qualities. Gasoline lacks this carboxyl group. Gasoline actually contains many different unique chains of hydrocarbons. When each is burned in a bomb calorimeter, the energy content of fat and gasoline are fairly similar. Fat contains about 9 Kcal per gram. Gasoline contains about 11 Kcal per gram.
- Energy is in the bonds that hold the atoms together, with the carbon to carbon bonds having a relatively high amount of molecular energy. When the carbon–carbon bonds are broken, energy is given off. Let’s compare the energy evolved when these bonds are broken in fat and in gasoline.
- In class I went over the combustion of fuel in a fire. To start a fire, we need a fuel, oxygen, and ignition in order to start the chain reaction that is needed to sustain a fire. How is metabolism in animals similar to combustion in a fire?
a. Substrates can be the same (Say fat in cells & biodiesel in a fire)
b. Both require oxygen
c. Both produce H2O and CO2
d. Both have energy evolved from the bonds in the substrates and the energy is converted to a different physical form.
6. Let’s first go over the basics of the evolution of energy in cells. The cell needs fuel, oxygen, and metabolic enzymes to generate a usable chemical/mechanical molecule. The diagram below, which is very simple compared to what really happens in a cell, shows how cells utilize the energy in the macronutrients. (1) Cells break the bonds and dismantle the macronutrients using a series of enzymatic reactions. The carbons are converted to CO2 and the electrons and hydrogen atoms are transferred to the mitochondrion using a series of transport molecules and proteins (depicted by the power lines)(2). In the mitochondrion, the energy in the electrons are used to synthesize ATP, a molecule the cell can use for chemical and mechanical purposes. Finally the electrons and hydrogens unite with oxygen to form water (3).
After exam 1 we will discuss metabolism and the formation of ATP.