Slide 1 In this tutorial we are going to begin talking about cellular respiration. Cellular respiration refers to the ability of cells to use the energy in a glucose molecule and convert that energy to energy in the form of ATP. Molecules besides glucose can be respired but we are going to look solely at the respiration of glucose.
Slide 2 To understand cellular respiration, we must understand the basics of chemical reactions known as redox reactions. Redox refers to oxidation and reduction which are reactions that involve the transfer of electrons from one compound to another. Oxidation is the loss of an electron or electrons and reduction is the gain of an electron or electrons.
Slide 3 Oxygen is highly electronegative which means it has a strong attraction for electrons. As we will see - it is this high electronegativity that allows us to get so much energy from a glucose molecule. We need oxygen because of its ability to pull electrons toward itself. When electrons move - energy is lost and gained. The oxidized compound loses energy when it loses electrons and the reduced compound gains energy when it gains electrons.
Slide 4 During cellular respiration, electrons move from a high energy state when they are part of the glucose molecule to a low energy state when they are grabbed by oxygen. It is the release of energy associated with the movement of electrons that cells use to generate ATP.
Slide 5 We can get an idea of the amount of energy that is available to cells by observing a combustion reaction. Methane is a high energy compound - in the presence of oxygen electrons are released from methane and travel to oxygen. This results in a large release of energy - in this case an explosive release of energy.
Slide 6 The explosive heat that is released from the combustion of a high energy compound like glucose is not useful for biological organisms. While organisms need a certain amount of heat to stay alive - heat itself is not a form of energy that can drive a cellular reaction. So rather than releasing energy in one explosive step - cellular respiration occurs in a series of small manageable steps.
Slide 7 The overall process of cellular respiration is an oxidation-reduction reaction in which glucose is oxidized to carbon dioxide and oxygen is reduced to water. The movement of electrons from glucose to oxygen releases energy and the cell can use that energy to produce ATP.
Slide 8 During cellular respiration, the movement of electrons must take place in small manageable steps. This means the cell needs an electron carrier molecule. This molecule is a molecule known as NAD+. Its job is to carry electrons from one stage of cellular respiration to the next. We can think of NAD+ as being like a dump truck and its job is to deliver loads of electrons to various stages of cellular respiration. The oxidized form of the molecule is NAD+ and we can think of it as being an empty dump truck. The reduced form is NADH and we can think of it as being a full dumptruck - it carries a load of electrons. This molecule is hugely important in the energy needs of a cell and it is an expensive molecule for cells to make. Just as you would not throw out a dumptruck after it delivers a load of supplies - a cell also does not throw out an NAD+ molecule after it has delivered a load of electrons. Conserving this molecule is important and this is an important idea to keep in mind as we continue to discuss cellular respiration.