Table of Contents. Section 1 Glycolysis and Fermentation. Section 2 Aerobic Respiration

Table of Contents Section 1 Glycolysis and Fermentation Section 2 Aerobic Respiration

Objectives Identify the two major steps of cellular respiration. Describe the major events in glycolysis. Compare lactic acid fermentation with alcoholic fermentation. Calculate the efficiency of glycolysis.

Harvesting Chemical Energy Cellular respiration is the process by which cells break down organic compounds to produce ATP. Both autotrophs and heterotrophs use cellular respiration to make CO 2 and water from organic compounds and O 2.

Harvesting Chemical Energy The products of cellular respiration are the reactants in photosynthesis; conversely, the products of photosynthesis are reactants in cellular respiration.

Harvesting Chemical Energy Cellular respiration can be divided into three stages: glycolysis, Krebs cycle (citric acid cycle) and electron transport chain.

Glycolysis Cellular respiration begins with glycolysis, which takes place in the cytosol of cells.

Glycolysis During glycolysis, one six-carbon glucose molecule is oxidized to form two three-carbon pyruvic acid molecules. A net yield of two ATP molecules is produced for every molecule of glucose that undergoes glycolysis.

Fermentation If oxygen is not present, some cells can convert pyruvic acid into other compounds through additional biochemical pathways that occur in the cytosol. The combination of glycolysis and these additional pathways is fermentation.

Fermentation Fermentation does not produce ATP, but it does regenerate NAD +, which allows for the continued production of ATP through glycolysis.

Fermentation Lactic Acid Fermentation In lactic acid fermentation, an enzyme converts pyruvic acid into another three-carbon compound, called lactic acid.

Lactic Acid Fermentation Pathway

Fermentation Alcoholic Fermentation Some plants and unicellular organisms, such as yeast, use a process called alcoholic fermentation to convert pyruvic acid into ethyl alcohol and CO 2.

Alcoholic Fermentation Pathway

Efficiency of Glycolysis Through glycolysis, only about 2 percent of the energy available from the oxidation of glucose is captured as ATP. Much of the energy originally contained in glucose is still held in pyruvic acid. Glycolysis alone or as part of fermentation is not very efficient at transferring energy from glucose to ATP.

Section 2 Aerobic Respiration Objectives Relate aerobic respiration to the structure of a mitochondrion. Summarize the events of the Krebs cycle. Summarize the events of the electron transport chain and chemiosmosis. Calculate the efficiency of aerobic respiration. Contrast the roles of glycolysis and aerobic respiration in cellular respiration.

Overview of Aerobic Respiration In eukaryotic cells, the processes of aerobic respiration occur in the mitochondria. Aerobic respiration only occurs if oxygen is present in the cell.

Overview of Aerobic Respiration The Krebs cycle occurs in the mitochondrial matrix. The electron transport chain (which is associated with chemiosmosis) is located in the inner membrane.

Pre-Krebs Cycle In the mitochondrial matrix, pyruvic acid produced in glycolysis reacts with coenzyme A to form acetyl CoA. Then, acetyl CoA enters the Krebs cycle. One carbon is removed from pyruvate. Coenzyme A is attached to the resulting 2-carbon sugar. This makes acetyl-coa. Acetyl-CoA enters the Krebs Cycle (Citric Acid Cycle).

The Krebs Cycle One glucose molecule is completely broken down in two turns of the Krebs cycle. These two turns produce four CO 2 molecules, two ATP molecules, and hydrogen atoms that are used to make six NADH and two FADH 2 molecules.

The Krebs Cycle The bulk of the energy released by the oxidation of glucose still has not been transferred to ATP.

Bottom Line o Reactants o Acetyl-CoA o Citrate (Citric Acid) o 6 NAD o 2 FAD o Products o Oxaloacetate o 6 NADH o 2 FADH 2 o CO 2

Running Tally! o Glycolysis o Krebs Cycle o 2 ATP o 2 ATP o 2 NADH o 6 NADH o 2 FADH 2 **So far aerobic respiration has only made 2 more ATP than an anaerobic organism can make.

Electron Transport Chain and Chemiosmosis Step #1 - High-energy electrons in hydrogen atoms from NADH and FADH 2 are passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane.

Electron Transport Chain and Chemiosmosis Step #1 - Protons (hydrogen ions, H + ) are also given up by NADH and FADH 2.

Electron Transport Chain and Chemiosmosis Step #2 - As the electrons move through the electron transport chain, they lose energy. Step # 3 - This energy is used to pump protons from the matrix into the space between the inner and outer mitochondrial membranes.

Electron Transport Chain and Chemiosmosis The resulting high concentration of protons creates a concentration gradient of protons and a charge gradient across the inner membrane.

Electron Transport Chain and Chemiosmosis Step #4 - As protons move through ATP synthase and down their concentration and electrical gradients, ATP is produced.

Electron Transport Chain and Chemiosmosis Step #5 - Oxygen combines with the electrons and protons to form water.

The Importance of Oxygen ATP can be synthesized by chemiosmosis only if electrons continue to move along the electron transport chain. By accepting electrons from the last molecule in the electron transport chain, oxygen allows additional electrons to pass along the chain. As a result, ATP can continue to be made through chemiosmosis.

Efficiency of Cellular Respiration Cellular respiration can produce up to 38 ATP molecules from the oxidation of a single molecule of glucose. Most eukaryotic cells produce about 36 ATP molecules per molecule of glucose. Thus, cellular respiration is nearly 20 times more efficient than glycolysis alone.

How many ATP are made? o Each NAD = 3 ATP o Each FAD = 2 ATP o It delivers at a lower step in the transport chain and so it produces fewer ATP. o Grand Total for ETC (alone) = 32 ATP o Glycolysis + Krebs + ETC = 36 ATP

A Summary of Cellular Respiration Another Role of Cellular Respiration Providing cells with ATP is not the only important function of cellular respiration. Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.

The Fate of Glucose o Recall how glucose passes through the cell membrane? (Facilitated Diffusion) Cells absorb glucose only because insulin triggers the cell membrane (via carrier protein) to begin allowing it into the cell.

The Fate of Glucose o If you have extra glucose it is turned into glycogen and stored in liver and muscles o To little glucose? Pancreas (via glucagon) signals release of stored glycogen o People with diabetes have difficulty with this process

Question: o You, however, can only last on stored glycogen for 12 Hours Then what? o How can a person live for 2 weeks without food if they can only last for 12 hours on stored glycogen?

ANSWER: o Because the body also stores protein and fat. o78% of total energy reserves is body fat (lipid) o21% of total energy reserves is in proteins.

Energy from Fats When blood glucose levels decline and glycogen stores are low, triglycerides are tapped as an alternative energy source. Enzymes in fat cells cleave the bonds between the glycerol and fatty acids, which enter the blood. Enzymes in the liver convert glycerol into PGAL (an intermediate of glycolysis)

Energy from Fats Enzymes cleave the backbone of the fatty acids. The fragments are converted to Aceytl CoA.

Fats have many more bonds than glucose. Glucose Glycerol FAT Palmitic acid, saturated fatty acid

Energy from proteins. Enzymes split amino groups from amino acids and ammonia is produced. Then it is excreted from the body in the form of urea. The carbon backbones can be converted to pyruvate, acetyl CoA, or they enter the Krebs cycle.

Multiple Choice Standardized Test Prep 1. Which of the following must pyruvic acid be converted into before the Krebs cycle can proceed? A. NADH B. glucose C. citric acid D. acetyl CoA

Chapter 7 Standardized Test Prep Multiple Choice, continued 1. Which of the following must pyruvic acid be converted into before the Krebs cycle can proceed? A. NADH B. glucose C. citric acid D. acetyl CoA Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Multiple Choice, continued 2. Which of the following is not a product of the Krebs cycle? A. CO 2 B. ATP C. FADH 2 D. ethyl alcohol Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Multiple Choice, continued 3. In which way is cellular respiration similar to photosynthesis? F. They both make G3P. G. They both involve ATP. H. They both involve chemiosmosis. J. all of the above Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Multiple Choice, continued 4. ATP is synthesized in chemiosmosis when which of the following moves across the inner mitochondrial membrane? A. NADH B. oxygen C. protons D. citric acid Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Summary o o o o o o Know the formula (overall) Know aerobic steps of respiration Know the ATP and NAD outputs of each pathway Know controls of Glycolysis Know anaerobic methods of respiration, and uses Know alternate entries of lipids and proteins into respiration

Chapter 7 Standardized Test Prep Multiple Choice, continued The illustration shows part of a biochemical pathway. Use the illustration to answer the question that follows. 6. This reaction occurs during which of the following processes? F. Krebs cycle G. acetyl CoA formation H. alcoholic fermentation J. lactic acid fermentation Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Multiple Choice, continued 7. glycolysis : pyruvic acid :: Krebs cycle : A. O 2 B. Oxaloacetate C. lactic acid D. acetyl CoA Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Multiple Choice, continued The illustration below shows some stages and reactants of cellular respiration. Use the illustration to answer the question that follows. 8. At which of the points is ATP, the main energy currency of the cell, produced? F. 1 only G. 2 only H. 1 and 3 J. 1, 2, and 3 Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Short Response The inner membrane of a mitochondrion is folded; these folds are called cristae. How might cellular respiration be different if the inner mitochondrial membrane were not folded?? Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Short Response, continued The inner membrane of a mitochondrion is folded; these folds are called cristae. How might cellular respiration be different if the inner mitochondrial membrane were not folded? Answer: The cristae increase the surface area of the inner wall of the mitochondria, which allows more electron transport chain pathways and ATP synthase. Thus, the rate of cellular respiration is increased. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Extended Response Oxygen is produced during the reactions of photosynthesis, and it is used in the reactions of cellular respiration. Part A How does oxygen get into or out of chloroplasts and mitochondria? Part B What are the roles of oxygen in the processes of photosynthesis and cellular respiration, and how are the roles similar? Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.

Chapter 7 Standardized Test Prep Extended Response, continued Answer: Part A Oxygen builds up inside chloroplasts as they produce oxygen, forming a concentration gradient high oxygen concentration inside and low concentration outside. This causes O 2 to diffuse out of the chloroplast. In mitochondria, as O 2 is used up, a favorable gradient for the inward diffusion of oxygen occurs. Part B In photosynthesis, oxygen is formed when water is split during the light reactions. This byproduct of photosynthesis is released by cells and becomes available for aerobic respiration. In aerobic respiration, oxygen is the final electron acceptor at the end of electron transport. When oxygen accepts these electrons (and protons), water is formed. Hence, water supplies oxygen for photosynthesis, and oxygen is used to form water in aerobic respiration. Chapter menu Resources Copyright by Holt, Rinehart and Winston. All rights reserved.