Lesson Objective: By the end of the lesson (s), I can: Vocabulary: 1. Describe the process of cell respiration, including reactants and products, glycolysis, the Krebs cycle, and the electron transport chain. 2. Distinguish between aerobic and anaerobic respiration. Lesson Question: Cellular respiration NADH Aerobic respiration NAD+ Lactic Acid fermentation Kilocalorie Acetyl CoA Oxaloacetic acid FAD Pyruvic Acid Anaerobic respiration Glycolysis Fermentation Alcoholic fermentation Mitochondrial matrix Krebs cycle citric acid 1. What are the steps involved in cellular respiration? 2. What are the differences between aerobic and anaerobic respiration? 3. Explain the role of organic compounds in cellular respiration. 4. Compare and contrast the products of lactic acid fermentation and alcoholic fermentation. 5. Calculate the efficiency of glycolysis if 12 kcal of energy are required to transfer energy from glucose to ATP. 6. For each six-carbon molecule that begins glycolysis, determine how many molecules of ATP are used and how many molecules of ATP are produced. 7. Construct a model that describes cellular respiration. 8. Construct a model that compares lactic acid fermentation to alcoholic fermentation. 9. Construct a model of the Kreb cycle 10. What is the relationship between the mitochondria and cellular respiration? Focus Question: 1. How do the structures of organisms enable life s functions? 2. How do organisms obtain and use the matter and energy they need to live and grow? 3. How do matter and energy move through an ecosystem? Overarching questions: 1. How do organisms live, grow, respond to their environment, and reproduce? 2. How and why do organisms interact with their environment, and what are the effects of those interactions?
Cellular Respiration 1) Glycolysis and Fermentation a) Harvesting Chemical Energy Cellular respiration is the complex precess in which cells make adenosine triphosphate (ATP) by breaking down organic compounds. Both autotrophs and heterotrophy undergo cellular respiration to breakdown organic compounds into simpler molecules to release energy. Some energy is used to make ATP which is then used by the cells to do work. The figure below shows that autotrophs and heterotrophs use cellular respiration to make CO 2 and water from organic compounds and oxygen. ATP is also made during cellular respiration. Autotrophs then use the CO 2 and water to produce oxygen and organic compounds. Therefore, we can say that the products of cellular respiration are the reactants in photosynthesis and conversely, the products of photosynthesis are the reactants of cellular respiration, Cellular respiration can be divided into 2 stages: Glycolysis (a) Stage in which organic compounds are converted into 3 carbon molecules of pyruvic acid, producing a small amount of ATP and NADH (an electron carrier molecule). This is an anaerobic process because it does not require the presence of oxygen. Aerobic respiration (a) If oxygen is present in the cell s environment, pyruvic acid is broken down and NADH is used to make a large amount of ATP through the process known as aerobic respiration Pyruvic acid can enter other pathways if there is not oxygen present in the cell s environment. The combination of glycolysis and these anaerobic pathways is called fermentation. Many of the reactions in cellular respiration are redox reactions. In redox reactions one reactant is oxidized (loses electrons) while another is
reduced (gains electrons). The following equation summarizes cellular respiration: b) Glycolysis Glcolysis is a biochemical pathway in which one six-carbon molecule of glucose is oxidized to produce 2 three carbon molecules of pyruvic acid. Series of chemical reactions catalyzed by specific enzymes. All reactions take place in the cytosol and occur in 4 main steps: Step 1 (a) 2 phosphate groups are attached to one molecule of glucose. (b) The phosphate groups are supplied by two molecules of ATP, which are converted into 2 molecules of ADP in the process. Step 2 (a) The six-carbon compound formed in step 1 is split into 2 three-carbon molecules of glyceraldehydes 3-phosphate (G3P). (also produced by the Calvin cycle in photosynthesis. Step 3 (a) 2 G3P molecules are oxidized, and each receives a phosphate group. (b) The product of this step is 2 molecules of a new 3-carbon compound. (c) The oxidation of G3P is accompanied by the reduction of 2 molecules of Nicotinamide Adenine dinucleotide (NAD + ) to NADH. NAD+ is similar to NADP+ a compound involved in the light reactions of photosynthesis. Like NADP+, NAD+ is an organic molecule that accepts electrons during redox reactions. Step 4 (a) The phosphate groups are added in steps 1 and 3 are removed from the 3- carbon compounds formed in step 3. (b) This reaction produces 2 molecules of pyruvic acid. (c) Each phosphate group s combined with a molecule of ADP to make a molecule of ATP. Because a total of 4 phosphate groups are added in step 1 and 3, 4 molecules of ATP are produced. (d) 2 ATP molecules were used in step 1, but 4 were produced in step 4. Therefore, the process of glyolysis has a net yield of 2 ATP molecules for every glucose molecule converted into pyruvic acid.
(e) c) Fermentation When oxygen is present cellular respiration continues as pyruvic acid enters the pathway of aerobic respiration. When oxygen is not present some cells covert pyruvic acid into other compounds through additional biochemical pathways inside the cytoplasm or cytosol. The combination of glycolysis and these additional pathways, which regenerate NAD+, is called fermentation. The fermentation process allows for the continued production of ATP. Two main types of fermentation: Lactic Acid Fermentation (a) In lactic cid fermentation an enzyme converts pyruvic acid made during glycolysis into a 3-carbon compound called lactic acid.
(b) In the figure above, lactic acid fermentation involves the transfer of one hydrogen atom from NADH and the addition of one free proton (H+) to pyruvic acid. NADH is oxidized to form NAD+. Then the NAD+ is used in glysoclysis where it is again reduced to NADH. (c) The regeneration of NAD+ in lactic acid fermentation helps to keep glycolysis going. (d) Lactic Acid fermentation is important in the dairy industry to create cheese, buttermilk, sour cream, yogurt, and other cultured dairy products.
Alcoholic Fermentation (a) Some plants and unicellular organisms, such as yeast, use a process to convert pyruvic acid into ethyl alcohol through alcoholic fermentation. (b) In the above figure, after glycolysis has started and has turned glucose into puruvic acid, a CO 2 molecule is removed from the pyruvic acid, leaving a 2- carbon compound. Next, two hydrogen atoms are added to the 2-carbon compoundto form ethyl alcohol. As in Lactivc fermentation, these hydrogen atoms come from NADH and H+, regenerating NAD+ for use in glcolysis. Genereally performed by yeast cells and used in the production of beer and wine, and in the production of bread. In the production of bread, CO2 that is produced by fermentation makes the bread rise by forming bubbles inside the dough while the ethyl alcohol evaporates during the baking process.
d) Efficiency of glycolysis Energy of often measured in units of kilocalories (kcal). Where 1 kilocalorie is equal to 1000 calories (cal). Scientist have calculated that the production of a standard amount of ATP from ADP absorbs a minimum of 7 kcal (depending on the conditions inside the cell). In the above equation: N is the number of glucose molecules, E ATP is the amount of energy required to transfer each molecule of glucose, and E REACT is the energy that it takes to oxidize one glucose molecule (686 Kilocalories). Glycolysis makes a net total of 2 ATP so the net efficiency of glycolysis is (2 x 7)/686 to get a percentage multiply by 100. Therefore you get an efficiency of about 2%. It is cleat that glycolysis alone or as a part of a fermentation process is not very efficient in transferring energy from glucose to ATP. Therefore, by themselves the anaerobic pathways and glycolysis are not enough to meet the energy demands of larger organisms. They require a more efficient pathway that is provided by aerobic respiration. 2) Aerobic Respiration a) Overview of Aerobic Respiration Aerobic respiration has 2 major parts: the Krebs cycle and the electron transport chain, which is associated with chemiosmosis (uses energy released by protons as they move across a membrane to make ATP. In the Krebs cycle oxidation of glucose that began with glycolysis is completed. Although the Krebs cycle produces a small amount of ATP, most of the ATP is produced during aerobic respiration is made through the activities of the electron transport chain and chemiosmosis. Aerobic respiration can ONLY take place in the presence of OXYGEN. This process starts in the cells. In prokaryotes the reactions of the Kreb cycle and electron transport chain take place in the cytosol of the cell. In eukaryotes, these reactions take place inside the mitochondria
The Krebs cycle (a) STEP 1 2-carbon molecule of acetyl CoA combines with a 4 carbon compound, Oxaloacetic acid to produce 6 carbon compound citric acid. This regenerates coenzyme A (b) STEP 2 Citric acid releases a CO 2 molecule and a hydrogen atom to form a 5 carbon compound. The electron in the hydrogen atom is transferred to the NAD+, reducing it to NADH. (c) STEP 3 The 5 carbon compound formed in step 2 releases a CO 2 molecule and a hydrogen atom, forming a 4 carbon compound. Again, NAD+ is reduced to NADH. Notice that in this step a molecule of ATP is also created from ADP. (d) STEP 4 The 4 carbon compound formed in step 3 releases a hydrogen atom to form another 4 carbon compound. This time hydrogen is used to reduce FAD to FADH 2. FAD or flavin adenine dinucleotide, is similar to NAD+ in that it accepts electrons during the reduction reaction. (e) STEP 5 4 carbon compound formed in step 4 releases a hydrogen atom to
regenerate oxaloacetic acid, which keeps the Krebs cycle operating. The electron in the hydrogen atom reduces NAD+ to NADH. This process happens to the 2 pyruvic acids created by glycolysis. The electron transport chain (a) STEP 1 Efficiency of Cellular respiration