BIOL1115 - Sp2024 - Chapter 9.docx

Chapter 9: Cellular Respiration and Fermentation ================================================ ### By the end of today's lesson, you should be able to: - **Explain the biological function of cellular respiration.** - **Distinguish between the following pairs of terms:** - **Oxidativ...

Chapter 9: Cellular Respiration and Fermentation ================================================ ### By the end of today's lesson, you should be able to: - **Explain the biological function of cellular respiration.** - **Distinguish between the following pairs of terms:** - **Oxidative vs. substrate-level phosphorylation** - Acetyl-CoA vs. coenzyme A (optional) - **Aerobic vs. anaerobic respiration** - Anaerobic respiration and fermentation (optional) - **Lactic acid vs. alcohol fermentation** - **Name the two electron carriers and explain that they accept electrons from glucose.** - **Name the four stages of cellular respiration, and answer the following questions for each stage, where applicable:** - **What are the reactants and products?** - **What happens to the carbon?** - **What happens to the energy that is released?** - **Where does this step occur?** - **Recognize examples of redox reactions and substrate-level phosphorylation that occur in this metabolic pathway.** - **Explain the role of the electron transport chain in cellular respiration.** - **Explain where and how the respiratory electron transport chain creates a proton gradient.** - **Explain how the proton gradient is used to generate ATP.** - **Describe how cellular respiration can be regulated.** - **Discuss how fermentation works and under what circumstances a cell will undergo fermentation.** - **Compare the efficiency of ATP synthesis by cellular respiration to that of fermentation.** Cellular Respiration: --------------------- - Living cells require *\_\_\_\_\_\_\_\_\_\_\_\_\_\_* from outside sources. *What is the source of energy that fuels your metabolism?* - Energy flows into an ecosystem as *\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_* and leaves as *\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_*. 1. 2. 3. 4. ***Review:** Is cellular respiration a catabolic or an anabolic pathway?* ***Review:** Is cellular respiration endergonic or exergonic?* - Although carbohydrates, fats, and proteins are all consumed as fuel, sugars are usually the primary consumed fuel. - The main sugar used in cellular respiration is glucose. - It is helpful to trace cellular respiration with the sugar \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. *Write the summary equation of cellular respiration.* ***Review:** What type of reaction is this? Explain.* ***Review:** Name the two electron carriers that are used in cellular respiration. Distinguish between the reduced and oxidized forms for each.* - *Chemical energy is stored in reduced molecules* like carbohydrates and lipids. - *The energy in these molecules is released [\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_] in a series of reactions.* - *The energy released is used to add a [\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_] group to ADP to make ATP.* ***Review:** What is the addition of a phosphate group to a molecule called?* - ATP phosphorylation can occur through \_\_\_\_\_\_\_\_\_\_\_\_ mechanisms during cellular respiration. - \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ phosphorylation - \_\_\_\_\_\_\_\_\_\_\_ ATP molecules are produced during the glycolysis and the citric acid cycle. - A phosphate group is removed from the reactant, and the free energy of the reaction is used to add the third phosphate to ADP, forming ATP. - \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_phosphorylation - Powered by redox reactions - It is responsible for almost \_\_\_\_\_\_\_\_\_ of the ATP generated by cellular respiration. Cellular Respiration: ------------------------------------------- - Cellular respiration has four stages: - **Glycolysis** (breaks down glucose into two molecules of pyruvate). - Processing pyruvate to acetyl-CoA - The **citric acid cycle** (completes the breakdown of glucose). - **Oxidative phosphorylation** (accounts for most of the ATP synthesis). *To summarize the process of cellular respiration, you should be able to answer the following four questions for each of the stages of cellular respiration:* 1. *Where does this stage occur?* 2. *What happens to the carbon atoms?* 3. *What happens to the electrons?* 4. *What is the energy yield?* ### Glycolysis: - Glycolysis ("splitting of sugar") breaks down glucose into two molecules of *\_\_\_\_\_\_\_\_\_\_\_\_\_*. - Glycolysis occurs in the cytoplasm and has three major phases: - *Energy-investment phase*. - Cleavage phase. - *Energy-payoff phase*. *In your own words, describe what is happening in each of these phases.* - Things to note: - Two ATP's are used at the beginning of glycolysis to *\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_* the glucose. - Glycolysis is regulated by feedback inhibition. - High levels of ATP [\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_] the third enzyme: phosphofructokinase. - Phosphofructokinase has two binding sites for ATP: - When ATP binds to the active site, the enzyme catalyzes the third step in glycolysis. - When ATP levels are [\_\_\_\_\_\_\_\_\_\_\_\_], it binds to a regulatory site and inhibits the enzyme. *Why is it necessary for ATP to bind to the active site for the third step to proceed?* *Why is it useful for the cell to inhibit this enzyme when ATP levels are high?* - The fourth step of glycolysis is the **\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ step**. - The molecule (formerly known as glucose) is broken into two pieces at this step. - Note that after the glycolytic step, everything is *multiplied by \_\_\_*. *Why do we multiply everything by two after the fourth step of glycolysis?* - Glycolysis produces *no CO~2~* and only *a little ATP*. - Therefore, pyruvate still contains a *substantial amount of \_\_\_\_\_\_\_\_\_\_\_\_\_\_*. - Glycolysis is technically \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. *Explain why glycolysis is anaerobic.* ### Pyruvate Processing: - In the presence of *\_\_\_\_\_*, pyruvate enters the mitochondrion. - Before the *citric acid cycle* can begin, pyruvate must be converted to **acetyl CoA**, which links the cycle to glycolysis. *For a single molecule of glucose undergoing cellular respiration, how many CO~2~ are released during the processing of pyruvate to acetyl CoA? What else is produced at this step (how many of each of these products are produced?)?* ### Citric Acid Cycle: - The citric acid cycle, also called the *Krebs cycle or the tricarboxylic acid (TCA) cycle*, takes place within the mitochondrial matrix. - The cycle oxidizes organic fuel derived from pyruvate, generating \_\_ ATP, \_\_ NADH, and \_\_ FADH~2~ per turn. *What is the total energy yield per glucose molecule?*  - The citric acid cycle has eight steps, each catalyzed by a specific enzyme. - The *acetyl group* of acetyl CoA joins the cycle by combining with *oxaloacetate*, forming *\_\_\_\_\_\_\_\_\_\_\_\_\_\_*. - The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle. - The NADH and FADH~2~ produced by the cycle relay *\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_* extracted from food to the electron transport chain. - Things to note: - It is the regeneration of oxaloacetate that makes this process a *\_\_\_\_\_\_\_\_\_\_\_\_\_*. - Although the citric acid cycle does not directly use oxygen, it *cannot function* under \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ conditions. - While there exists a mechanism to re-oxidize NADH in the absence of O~2~, FADH~2~ can only be re-oxidized when oxygen is available. - Glycolysis is the only stage of cellular respiration which can function *anaerobically*. - Note that CoA is actually used at *two steps* of the citric acid cycle. - Both times CoA acts as an *agent* to drive an \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ step forward. *In the reactions so far, what is the net production of ATP per glucose molecule?* *Where is most of the energy stored at this point?* ### Oxidative Phosphorylation: Electron Transport Chain and Chemiosmosis: ***Review:** Draw a mitochondrion. Label the following structures: cristate, inner mitochondrial membrane, intermembrane space, mitochondrial matrix, and outer mitochondrial membrane.* - Electrons are transferred from \_\_\_\_\_\_\_\_\_ or \_\_\_\_\_\_\_\_\_ to the *electron transport chain*. - The electron transport chain is located in the *\_\_\_\_\_\_\_\_\_\_\_* of the mitochondrion. - Electrons are passed through a number of proteins to O~2~. - Most of the chain's proteins exist in multi-protein complexes. - The carriers alternate *\_\_\_\_\_\_\_\_\_\_\_\_\_* and *\_\_\_\_\_\_\_\_\_\_\_\_\_\_* states as they accept and donate electrons. - Electrons drop in free energy as they go down the chain. - At the end of the electron transport chain, electrons are finally passed to O~2~, forming H~2~O. - The electron transport chain generates no \_\_\_\_\_\_\_\_\_. - The chain's function is to break the large *free-energy drop* from food to O~2~ into smaller steps that release energy in manageable amounts. - Electron transfer in the electron transport chain causes proteins to \_\_\_\_\_\_\_\_ *H^+^* from the mitochondrial matrix to the intermembrane space. - The H^+^ gradient is referred to as a proton-motive force, emphasizing its capacity to do \_\_\_\_\_\_\_\_\_\_\_\_. - The energy stored in a H^+^ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis. ***Review:** In an active mitochondrion, is the pH higher in the mitochondrial matrix or in the intermembrane space? Explain.* - H^+^ then moves back across the membrane, passing through channels in **ATP synthase**. - ATP synthase uses the exergonic flow of H^+^ to drive *\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ of ATP*. - This is an example of **chemiosmosis.** - **Chemiosmosis is** the use of energy in a *H^+^ \_\_\_\_\_\_\_\_\_\_\_\_\_* to drive cellular work. ***Review:*** *In your own words, summarize the process of oxidative phosphorylation.* - During cellular respiration, most energy flows in this sequence: ***Review:** In your own words, explain this statement.* ***Review:** Describe the flow of electrons during cellular respiration.* Fermentation and Anaerobic Respiration: --------------------------------------- *What is the net ATP yield of glycolysis?* *What is required to keep glycolysis running? How is this normally achieved?* - Most cellular respiration *requires \_\_\_\_\_* to produce ATP. - Glycolysis can produce ATP *with or without O~2~* (in aerobic or anaerobic conditions). - In the absence of O~2~, glycolysis couples with fermentation or anaerobic respiration to produce ATP. - Anaerobic respiration uses an *electron transport chain* with an *\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ acceptor* other than O~2~, for example sulfate. ***Review:** List another example of a terminal electron acceptor.* - Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP. - Fermentation consists of glycolysis plus reactions that *regenerate\_\_\_\_\_\_\_\_\_,* which can be reused by glycolysis. - Two common types are *alcohol fermentation* and *lactic acid fermentation*. - In **lactic acid fermentation**, pyruvate is reduced to *\_\_\_\_\_\_\_\_\_\_\_\_* to oxidize NAD^+^. No release of CO~2~. *List two examples of lactic acid fermentation.* - In **alcohol fermentation**, pyruvate is converted to *\_\_\_\_\_\_\_\_\_\_\_\_\_\_* in two steps, while releasing *\_\_\_\_\_\_*. *List two examples of alcohol fermentation.* *Fill in the table below with information on two major differences between fermentation and cellular respiration.* **Fermentation** **Cellular Respiration** -------------------------------- ------------------ -------------------------- **Terminal Electron Acceptor** **Number of ATP Produced** ***At home activity:** Fill in the table for each stage based on the oxidation of one glucose molecule (i.e., how many ATP, CO~2~, etc. are produced in each stage?).* **Stage of Cellular Respiration** **Where does this stage occur?** **What is happening to the carbons?** **What is happening to the electrons?** **What is the net energy yield? (Consider [all] high energy products)** ----------------------------------- ---------------------------------- --------------------------------------- ----------------------------------------- ------------------------------------------------------------------------------------- Glycolysis Pyruvate processing Citric Acid Cycle Oxidative Phosphorylation