Metabolism Part 2

1. MetabolismPart 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.)

2. 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.

3. Glucose 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

4. 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.

5. 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

6. 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.

7. 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!

8. 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.

9. 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.

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

11. 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.

12. Summary of Glycolysis

13. 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.

14. 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

15. 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.