Biology Homework Chapter 6:
Cellular Respiration and Glycolysis
Textbook assignment: Chapter 6: How Cells Harvest Energy, sections 1-10.
- 6.1 The two key energy reactions of organic matter are photosynthesis, which captures light energy and stores it as chemical energy, and cellular respiration, which releases chemical energy to do work and generate heat.
- 6.2 Distinguish between breathing (drawing air into the lungs to exchange oxygen and carbon dioxide), and cellular respiration, the combustion of oxygen (supplied by breathing respiration) within the mitochondria of the cell to produce ATP.
- 6.3 Review ATP molecules from 5.4 if necessary. Cells use some ATP to support the respiration process, but produce more than they use. Although some heat is lost in the process (as it must be, according to the second law of thermodynamics), the process is more efficient that most mechanical ones engineered by humans.
- 6.4 All human activity depends on ATP its a source of energy; different activities "burn" this energy at different rates.
- 6.5 Cellular respiration is a chemical reaction where the atoms in sugar and oxygen molecules are rearranged through a series of enzyme controlled steps. At each step, electrons wind up in a state of lowered stored potential energy. The released energy is stored by phosphorylation in ATP's bonds.
Since electrons change their allegiance from one nucleus to another, these reactions are oxidation-reduction reactions. The loss of electrons is called oxidation, because this phenomenon was originally recognized in reactions where oxygen combined with some atoms or molecules. The gain of electrons is called reduction, because the atoms gaining the electrons now have reduced reactivity. (Since their electron orbitals are now full, they have further no tendency to combine with other atoms.) The electrons are carried from one atom to another by NAD+, a molecule that acts as a catalyst (something that enables a reaction but does not itself change with the reaction).
The last part of the reaction involves NADH releasing electrons to the membrane of the mitochondria, where the electron is passed from one receptor molecule to another and finally inside the cell to an oxygen molecule. Each receptor molecule takes some energy from the electron.
In the process of chemiosmosis, energy harvested by the receptor molecules is used in phosphorylation to make ATP out of AMP and ADP. In substrate phosphorylation, a phosphate is broken from some source molecule and directly combined with ADP. The two processes produce different amounts of energy.
- 6.6 The main phases of the cellular respiration cycle are glycolysis (breaking up glucose), the Krebs cycle (rearranging molecules), and chemiosmosis (transport of the electron through the chain of receptor molecules in the membrane).
- 6.7 Glycolysis is an oxidization-reduction reaction. The glucose molecules gain electrons (oxidization) which allows them to break apart. Substrate-level phosphorylation attaches a phophate group to a molecule, in this case, to ADP, making it ATP.
- 6.8 Focus on understanding how the different steps in the reaction diagram require energy (taking in ATP and breaking it down to ADP, or creating ATP with excess energy). Learn to recognize from the diagram when ATP is required or released, when phosphorylation occurs, and when other products are created.
- 6.9 Glycolysis produces pyruvate, but the pyruvate cannot procede to the next set of reactions without some processing. In this intermediate step, each pyruvate molecule loses a carbon dioxide molecule. The remaining 2-carbon chain attaches itself to a complex called Coenzyme A, which can transport it to a site where the next sequence of reactions begins: the Krebs cycle.
- 6.10 In the Krebs or citric acid cycle, the 2-carbon molecule attached to AcetylCoA is taken on by a group of molecules which rearrange it, hooking it to a 4-carbon molecule called oxaloacetate. The 6-carbon result, citrate, loses one carbon and some oxygen as carbon dioxide and becomes a 5-carbon chain, alpha-ketoglutarate. This molecule loses a carbon as part of carbon dioxide, and the remaining succinate molecule is rearranged back to oxaloacetate -- read to take on another 2-carbon acetyl Coenzym A complex. But at each step of this reaction path, energy is stored in NADH and ATP as the higher-energy electrons in the original 2-carbon chain are siphoned of their energy. At the end, we have oxaloacetate again, two carbon dioxide molecules, some ATP, and some high-energy electrons stored in NADH and FADH2 that can now be harvested in the final process: oxidative phosphorylation.
Read the following weblecture before chat: Cellular Respiration I
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
- Use the animations at the Sumanasinc site to investigate
- The Big Picture
- The Citric Acid Cycle
- Use the short animations at HHMI to get a better sense of how these two operations occur in the cell:
- Optional Website: Here's another overview of cellular respiration that may help you recognize where each phase takes place. Click on the labels for explanations of the terms.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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