Metabolism Part 2 I teach a simplified version of Glycolysis and Tricarboxylic Acid Cycle (Kreb Cycle). I don’t want to you spend any time memorizing chemical structures, I simply want you to understand the concepts behind the 2 cycles. Once you understand the concepts behind the cycles then you will better understand them in more detail. (Which you will get in other classes, not this one.)

Glycolysis Here are a couple of important definitions for you to know before we begin. Oxidation: this means that a molecule has lost electrons Reduction: this means that a molecule has gained electrons Glycolysis is the is the process of breaking glucose down into 2 molecules of pyruvate (also referred to as pyruvic acid). Glucose is a sugar that is composed of 6 carbons (6 Cs) and multiple oxygen (O) and hydrogen (H). Pyruvate is a molecule that is composed of 3 Cs, O, and H. Simply put, Glycolysis is the formation of 2 molecules of pyruvate through the oxidation of glucose. (A 6C molecule is split into 2, 3 carbon molecules.

Glucose Pyruvate Pyruvate O OH OH OH OH H H C C C C C C H OH Lose 1 H2O Lose 1 H2O C C C C C C Pyruvate Pyruvate

In the process of forming pyruvate some H and O molecules are lost as water. 2 molecules of ATP are used in the process of splitting glucose. By the time the process is finished, 4 ATP are made. The Net Energy that is produced by this process is 2 ATP.

Before pyruvate can then enter the Tricarboxylic Acid Cycle (TCA Cycle) it has to be changed slightly. It changes from a 3 C molecule to a 2 C molecule. The first CO2 is released and Coenzyme A is added on. If the acetyl CoA is not added, the molecule can’t fit into the TCA cycle because it is not the right shape. O H O H OH C C C H C C H O H S-CoA H CO2 is lost Acetyl CoA Pyruvate

TCA Cycle Now the Acetyl CoA can fit into the TCA cycle and continue it’s journey. Remember that each glucose gives us 2 molecules of pyruvate. Each pyruvate is converted to Acetyl CoA. During the conversion process 1CO2 is lost from each pyruvate. So, from the original 6 Cs of glucose we now have 4 remaining. We have also lost some H and O as water during Glycolysis, as well as some additional O as CO2.

The TCA results in the complete oxidation of acetyl CoA to CO2 The TCA results in the complete oxidation of acetyl CoA to CO2. In other words, all 4 Cs and the O from the acetyl CoA are lost as CO2 by the time it is finished with the TCA cycle. 1 ATP is made per Acetyl CoA molecule that enters the TCA Cycle. So a total of 2 ATP are made during the TCA Cycle per molecule of glucose. Once the C and O are gone, there are still a few H left. Normally a H molecule is a composed of 1 proton and 1 neutron and 0 electrons. During the TCA Cycle, the H molecules are left with 1 electron each. These H molecules with their corresponding electrons are the most important part of aerobic metabolism!

Special taxis called, NAD+ and FAD, come and pick up the molecules of H with their corresponding electrons and take them to the Electron Transport Chain. NAD+ can carry 1 H with its corresponding electron and FAD can carry 2 Hs with their corresponding electrons.

Electron Transport Chain The carrier molecules NAD+ and FAD bring the H’s to cell membrane (in prokaryotes) or the mitochondrial membrane (in eukaryotes). The H’s and their corresponding electrons are released into the cell membrane at the sight of a proton that specializes in pumping the H’s outside of the cell membrane. The electrons are passed through a series of proteins (via oxidation and reduction reactions) inside of the cell membrane, called the Electron Transport Chain.

Outside the Cell Cell Wall Cell Memrane + Inside the Cell e- e- e- e- ATP Synthase H+ e- Cell Memrane e- e- e- e- H oxygen NAD-H H+ NAD+ e- + oxygen H+ + = H2O Inside the Cell

Once the electrons have moved through the electron transport chain they are transported to a molecule called, the Terminal Electron Acceptor. In the case of Aerobic Respiration, the Terminal Electron Acceptor is oxygen. Excess H’s (now called protons because they are no longer carrying an electron) outside the cell membrane create potential energy because there is a high positive charge on one side of membrane. These protons are then pumped back inside the cell through the enzyme ATP Synthase. The movement of the protons through ATP Synthase powers the enzyme to make ATP. Then the protons, electrons and terminal electron acceptor combine to form water. Net result = 34 ATP + 4 ATP from glycolysis and kreb cycle = 38 ATP in prokaryotes. In addition, H2O and CO2 are given off as the by products of respiration/metabolism.

Electron Transport Chain Summary of Glycolysis Start with End With Net ATP Generated Glycolysis 1, 6C glucose 2 ATP 2, 3C pyruvate 4 ATP TCA Cycle 2, 3C Pyruvate Co2, ATP, H with e-s Electron Transport Chain H with e-s H2O, ATP 34 ATP Total=38 ATP

Anaerobic Respiration Anaerobic Respiration is essentially the same as aerobic respiration. The main difference is that the terminal electron acceptor is a compound other than O2. It is usually some compound that contains nitrogen, sulfur, or carbon. Ie. Nitrate, nitrite, sulfate, or carbonate It does not generate as many ATP as aerobic respiration.

Fermentation Anaerobic Respiration and Fermentation are not the same thing. Anaerobic Respiration still utilizes the TCA cycle but fermentation only utilizes glycolysis. After pyruvate is generated through glycolysis, it is then converted to some acid or alcohol by product. Fermentation does not require oxygen to occur. Fermentation does not require the TCA cycle. It uses organic compounds as the terminal electron acceptor. It produces only small amounts of ATP. Examples of end products are lactic acid or ethanol

This completes the lecture material for Unit 1. I will be happy to stay after lab and answer any questions regarding the material for Test 1 or to conduct a review. I will post a review sheet Monday morning, Sept. 25.