Unit 05: Cell Respiration

 

Helpful web sites:

Good diagrams
John Kyrk animations
More animations

Now that you have had an introduction to the basic structure of the eukaryotic cell, we will begin a series of chapters that go into the complex functions of those cells. This material will depend heavily on the previous unit on macromolecules as well. In this unit we will largely concentrate on the inner workings of the mitochondria and their role in cell respiration. It is important that you be familiar with the structure of these organelles, the chemical structure of ATP its function as an "energy carrier."

Learning Objectives: the successful student will be able to ...

• write the overall balanced equation for cell respiration.
• list and describe the major events that occur in the three stages of cell respiration.
• explain the difference between aerobic and anaerobic respiration and relate these terms to the events of cell respiration.
• describe the modification of cell respiration that occurs in alcoholic and lactic acid fermentation. 
• Relate the double membrane structure of the mitochondria to the the events that take place in the electron transport chain.
• Explain the role of membrane proteins in the electron transport chain, especially the proton pumps, electron carriers, and ATP synthase.
• Describe the role of oxygen as the final electron acceptor in aerobic respiration.

Lesson One: Review and Background Information.

Go to the Online Biology book and review the structure and vocabulary of the mitochondrium. The distinction between the inner and outer membranes and the intermembrane space and matrix become very important in this unit. In Kimball, review the structure of the ATP molecule. Recall the special nature of the covalent bonds between the phosphate groups and ATP's function as the "energy molecule." 

We will study photosynthesis in our next unit, but recall that it takes place some bacteria and in the chloroplasts of autotrophic organisms (plants and protista). You need to be able to write the balance overall equation for photosynthesis.

Energy (e.g. Sunlight) +  6 H₂O   +   6 CO₂  →   C₆H₁₂O₆   +   6 O₂ 

and the same for cell respiration that takes place in the cells of all organisms, autotrophs and heterotrophs.

C₆H₁₂O₆   +   6 O₂   →    6 H₂O   +   6 CO₂   +   ATP

Notice the relationship between these two processes; one producing the reactants for the other. This relationship is called the Carbon-Oxygen cycle.

Homework, Due  15 November. Go to the Visonlearning page on the Carbon cycle. Read this material and pay particular attention to the "natural" processes that cycle carbon (and oxygen) and the role of human activity in the carbon cycle. Write a brief paragraph explaining how wide spread burning of forest to clear land for cattle grazing and extracting coal and oil to burn as fuel disrupt the balance of the carbon-oxygen cycle. Email your work using your FBA account.

 

Lesson Two: An Overview of Cell Respiration.

In this lesson we look at the general process of cell respiration to understand the different stages of the process, where they take place, the structures involved, and to get an idea of the amount of ATP produced. Go to the Online Biology text and read the material there. Don't worry about fermentation for now; we deal with that later. Focus on the sections: Glycolysis, Aerobic Respiration, Transition Reactions, Krebs Cycle, and Electron Transport Phosphorylation. Note that the classification of these steps of cell respiration is somewhat arbitrary. Different writers combine some of these steps (e.g. the Krebs cycle and electron transport). What matters is understanding the events of each step and their relationship to one another. Here is another web site that may be helpful. Scroll down to unit 14 and follow the links to the various steps of cell respiration.

Homework, Due 17 November. For each of the steps of cell respiration listed above write the following information. Email your answers using your FBA account.

1. the location in the cell where the steps take place.
2. the starting reactant.
3. the end product.
4. the presence of oxygen/or not.
5. the amount of ATP used up.
6. the amount of ATP produced.

 

Lesson Three: The Electron Carriers, NAD+ and FAD+.

As the process of glycolysis moves from the initial reactant of glucose to the final product of pyruvate you should have learned that a total of 4 ATP molecules were produced. Since two ATP were consumed in the beginning steps, this yields a net gain of 2 ATP for glycolysis. However, the production of ATP from glycolysis is not finished, only delayed. Recall that the 3-carbon molecules produced react with a molecule called NAD+. This is an electron carrier which strips away electrons from organic molecules, carries those electrons to the electron transport system (ETS), which then in turn uses that energy to make more ATP. Go to this link and read a general description of the function of NAD+ and FAD+. Go here to see the structure of NAD+ and NADH and here to see the structure of FAD+ and FADH₂.

Homework, Due 22 November. Email answers to the following questions using your FBA account.

1. Look carefully at the structures of NAD+ and FAD+ in the links above. What components do these two molecules share in common with ATP?
2. For both carriers, how many electrons do they accept when they are reduced?
3. For both carriers, how many hydrogen atoms are actually bonded to the carrier molecule?
4. Once reduced to NADH and FADH₂, where do these molecules go? 

 

Lesson Four: The Aerobic Pathways.

We finish our discussion of aerobic cell respiration with the pathways that follow glycolysis; the transition between glycolysis and the Krebs Cycle, the Krebs Cycle, and the Electron Transport System (ETS). Go to Online Biology for a general summary. The key points to focus on here are the loss of Carbon in the form of CO2, the role of the electron carriers (where they appear and where they go), and the fate of the high energy electrons and H+ ions in the ETS. These animations that we have used in class is a good place to view these processes step by step (scroll down to animations 8.2a to 8.2d).

Homework, Due 28 November.  Email your answers to the following questions using your FBA account.

• Explain why the Krebs Cycle and the electron transport system could not work if mitochondria were not double membrane structures. Be specific.
• Explain the role of passive and active transport in the production of ATP in the mitochondria.
• Explain how the events that take place in the ETS are an excellent example of the first and second laws of thermodynamics.