1. The capture of energy: Autotrophs vs. Heterotrophs
   1. “Foodstuff” and ATP. Among the wide diversity of organisms there are numerous metabolic pathways that are involved in the breakdown (catabolism) of organic molecules for the production of ATP. As you should remember, ATP is the form of chemical energy that cells use to run their metabolic processes (e.g. active transport, muscle movement, etc.). We will examine one of these reactions that involves the catabolism of glucose in an aerobic eukaryotic cell. Cells can harvest energy from many other carbon molecules, and we will briefly introduce these pathways at the end of the discussion. You should be aware that most cells can enzymatically modify most “foodstuffs” into glucose.
   2. Oxidative and Substrate-Level Phosphorylation: In our previous discussion we examined the process of photophosphorylation. In this chapter we will look at two processes:
      1. Oxidative Phosphorylation: In the presence of oxygen, most organisms are capable of generating large quantities of reduced ATP for cellular use. Oxidative phosphorylation refers to the synthesis of ATP by a process called chemiosmosis. We will examine this in detail later.
      2. Substrate-Level Phosphorylation: In the reactions we are about to examine, we will see that a donor molecule (e.g. a sugar) can be oxidized and react to form ATP from ADP. These reactions are exergonic and enzyme-mediated. Relative to oxidative phosphorylation, this type of phosphorylation is inefficient and crude. Most cells could not gain enough energy from substrate-level phosphorylation to maintain their bodies. Be aware that as well as the production of ATP, the catabolic reactions discussed today can also lead to the reduction of energy carriers. This is obviously (??!!?) coupled to the oxidation of the “food” molecule being catabolized.
         note: you must always be aware of energy transfer in the reactions we study. Know if a reaction(s) that produces ATP is oxidative or substrate level.
   3. Anaerobic Conditions (Without O₂)
      1. Fermentation: We will examine the two fermentative pathways in your text. As we go over these reactions be aware of two things:
         1. NADH from glycolysis is oxidized...why so important?
         2. End products are relatively high energy
      2. Anaerobic Electron Transfer w/ Alternate Final Electron acceptors. You will see the importance of oxygen in aerobic energy harvest. With oxygen acting as a final electron acceptor, cells can generate many times the ATP from a single glucose than fermenters. Certain bacteria are capable of anaerobic catabolism of glucose that is similar to aerobic harvest, in that an electron transport system develops ATP by chemiosmosis. However, these organisms utilize alternate final electron acceptors such as carbonate ions. We will not cover these reactions in any detail.

   4. Redox Reactions (review):
      1. Coupled Oxidation and Reduction
      2. NAD and FAD

   5. The Reactions that Comprise the Catabolism of Glucose
      1. Glycolysis: The stage of “glucose splitting” occurs in the cytoplasm of the cell. Millions of glucose molecules are catabolized in the cell every second. The more energy demanding the cell, the faster the rate of catabolism must be. Some other molecules can also enter the series of reactions that we call glycolysis, e.g. fatty acids, amino acids, etc.. Glycolysis is a series of enzyme- mediated chemical reaction that results in two pyruvate (pyruvic acids) molecules, the phosphorylation of 2ADP’s (by substrate-level phosphorylation), and the reduction of 2NADH’s. Therefore, the reaction is overall an exergonic reaction. You must realize that the two pyruvic acids have less stored potential chemical energy than one glucose...ask if you do not understand. Know products and reactants. One last thing; you will not have to learn the intermediates in the glycolysis reaction. You should be aware that although the reaction results in the net production of 2ATP molecules, there are actually two ATP’s used and four produced.
      2. Pyruvate Oxidation (intermediate step): The two pyruvate are further oxidized to acetyl Co-A. Carbon Dioxide is liberated and NADH (x2...why?) is formed. I will go over this reaction in class. Write down the reactants and products for this reaction.
      3. Kreb’s Cycle (Citric Acid Cycle): From the same Figure as above, we will go over this cycle. The products of those millions of glycolysis are continuously channeled into the reactions of pyruvate oxidation and Kreb’s. These reactions occur in the mitochondrial matrix after pyruvic acid is transported into the cell. Acetyl Co-A enters the Kreb’s cycle, enzymatically combining with a four carbon oxaloacetate molecule to form citric acid (hence the name). Through a series of oxidation/reduction reactions and carboxylation (loss of carbon), the cycle begins again. You can think of the two carbon entering the cycle and leaving as two carbon dioxide molecules. The cycle is extremely exergonic, resulting in the production of one ATP (substrate-level), reduction of one FAD, and the reduction of 3 NAD. Important: since the cycle occurs twice (2 x pyruvic acids), we must double the products of the cycle. You are only responsible for the detail in this handout.
      4. Electron Transport: The Respiratory Chain and Chemiosmosis; the reactions of the ETS are elaborate and sophisticated method for harvesting the energy in the form of energized (reduced) electron carriers. These reactions occur continuously along the inner membranes of the mitochondria (outer plasma membrane in bacteria). The source of energy that run the ETS are the reduced electron carriers of glycolysis, pyruvate oxidation, and Kreb’s. It is vital that you recognize that if the ETS cannot operate (no oxygen for instance), most cells will die from a lack of ATP; the energy remains “locked” in the energy carriers that cannot be oxidized. In cells that are very energy demanding (muscle and nerve) cells, there are many mitochondria that continuously oxidize reduced energy carriers in the harvest of much ATP. You should be aware that the ETS is completely dependent on the reactions of glycolysis, pyruvate oxidation, and Kreb’s as a source of electrons. Make sure you take notes on the process of chemiosmosis and oxidative phosphorylation.

   6. ATP calculations: Take notes.

   7. Catabolism of other carbon molecules: We will examine the figures in your text or from handouts.