Cellular Respiration Handout PDF

TOPIC: CELLULAR RESPIRATION A. AEROBIC VS ANAEROBIC RESPIRATION Most Essential Learning Competency The learners differentiate aerobic from anaerobic respiration. (STEM_BIO11/12-IIa-j-6) Aerobic respiration, a process that uses oxygen, and anaerobic respiration, a process that do...

TOPIC: CELLULAR RESPIRATION A. AEROBIC VS ANAEROBIC RESPIRATION Most Essential Learning Competency The learners differentiate aerobic from anaerobic respiration. (STEM_BIO11/12-IIa-j-6) Aerobic respiration, a process that uses oxygen, and anaerobic respiration, a process that doesn't use oxygen, are two forms of cellular respiration. Although some cells may engage in just one type of respiration, most cells use both types, depending on an organism's needs. Aerobic respiration is the process of cellular respiration that uses oxygen to produce energy from food. This type of respiration is common in most plants and animals, including humans, birds and other mammals. Anaerobic means “without air”. Therefore, this type of cellular respiration does not use oxygen to produce energy. Anaerobic respiration usually occurs in lower plants and microorganisms. In the absence of oxygen, the glucose derived from food is broken down into alcohol and carbon dioxide along with the production of energy. Comparison of Aerobic and Anaerobic Respiration CRITERIA AEROBIC RESPIRATION ANAEROBIC RESPIRATION Definition Aerobic respiration uses oxygen. Anaerobic respiration is respiration without oxygen; the process uses a respiratory electron transport chain but does not use oxygen as the electron acceptors. Cells that use it Occurs in most cells. Occurs mostly in prokaryotes Amount of energy released Higher (36-38 ATP molecules) Lower 2 ATP molecules Stages Glycolysis, Krebs cycle, Electron Transport Chain Glycolysis, Krebs cycle, Electron Transport Chain Site of reactions Cytoplasm and mitochondria Cytoplasm and mitochondria Reactants glucose, oxygen glucose, electron acceptor Products Carbon dioxide, water, ATP Carbon dioxide, ethanol or lactic acid, ATP Combustion Complete Incomplete B. STAGES OF CELLULAR RESPIRATION Most Essential Learning Competencies The learners explain the major features and sequence the chemical events of cellular respiration. (STEM_BIO11/12-IIa-j-7) The learners distinguish major features of glycolysis, Krebs cycle, electron transport system, and chemiosmosis. (STEM_Bio11/12-IIa-j-8) Describe reactions that produce and consume ATP. (STEM_Bio11/12-IIa-j-9) Cellular Respiration Cellular respiration is a process of energy conversion where carbohydrates (glucose) are broken down into carbon dioxide, water, and energy (ATP) It takes place in both the cytosol and mitochondria of cells. This reaction can be grouped into three main stages and an intermediate stage: glycolysis, transformation of pyruvate, the Krebs cycle (also called the citric acid cycle), and oxidative phosphorylation. 1. Glycolysis Occurs in the cytosol It is series of reactions which break the 6 – carbon glucose molecules down into two 3 – carbon molecules called pyruvate Glycolysis takes place in both aerobic and anaerobic organisms and is the first step toward the metabolism of glucose. This process is an ancient one – all organisms from simple bacteria to humans performs it the same way. The word glycolysis means “glucose splitting,” which is exactly what happens in this stage. General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. Step 1 Phosphorylation of glucose The glucose is initiated or primed for the subsequent steps by phosphorylation at the C6 carbon. The process involves the transfer of phosphate from the ATP to glucose forming Glucose-6-phosphate in the presence of the enzyme hexokinase and glucokinase (in animals and microbes). This step is also accompanied by considerable loss of energy as heat Step 2: Isomerization of Glucose-6-phosphate Glucose 6-phosphate is reversibly isomerized to fructose 6-phosphate by the enzyme phosphohexoisomerase/phosphoglucoisomerase. This reaction involves a shift of the carbonyl oxygen from C1 to C2, thus converting an aldose into a ketose. Step 3: Phosphorylation of fructose-6-phosphate This step is the second priming step of glycolysis, where fructose-6-phosphate is converted into fructose-1,6-bisphosphate in the presence of the enzyme phosphofructokinase. Like in Step 1, the phosphate is transferred from ATP while some amount of energy is lost in the form of heat as well. Step 4: Cleavage of fructose 1, 6-diphosphate This step involves the unique cleavage of the C-C bond in the fructose 1, 6-bisphosphate. The enzyme fructose diphosphate aldolase catalyzes the cleavage of fructose 1,6-bisphosphate between C3 and C4 resulting in two different triose phosphates: glyceraldehyde 3-phosphate (an aldose) and dihydroxyacetone phosphate (a ketose). Step 5: Isomerization of dihydroxyacetone phosphate In this step, dihydroxyacetone phosphate is isomerized into glyceraldehyde 3-phosphate in the presence of the enzyme triose phosphate isomerase. This reaction completes the first phase of glycolysis. Step 6: Oxidative Phosphorylation of Glyceraldehyde 3-phosphate The glyceraldehyde 3-phosphate is converted into 1,3-bisphosphoglycerate by the enzyme glyceraldehyde 3-phosphate dehydrogenase (phosphoglyceraldehyde dehydrogenase). Step 7: Transfer of phosphate from 1, 3-diphosphoglycerate to ADP It involves the transfer of phosphate group from the 1, 3-bisphosphoglycerate to ADP by the enzyme phosphoglycerate kinase, thus producing ATP and 3-phosphoglycerate. Step 8: Isomerization of 3-phosphoglycerate The 3-phosphoglycerate is converted into 2-phosphoglycerate due to the shift of phosphoryl group from C3 to C2, by the enzyme phosphoglycerate mutase. This is a reversible isomerization reaction. Step 9: Dehydration 2-phosphoglycerate In this step, the 2-phosphoglycerate is dehydrated by the action of enolase (phosphopyruvate hydratase) to phosphoenolpyruvate. This is also an irreversible reaction where two moles of water are lost. General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. Step 10: Dehydration 2-phosphoglycerate Phosphoenolpyruvate is converted into an enol form of pyruvate by the enzyme pyruvate kinase. The enzyme catalyzes the transfer of a phosphoryl group from phosphoenolpyruvate to ADP, thus forming ATP. Product of Glycolysis 2 Pyruvate 2 NADH 2 ADP 4 ATP 2 ATP net gain , Fate of Pyruvate In aerobic organisms, the pyruvate is then moved to the mitochondria where it is oxidized into the acetyl group of acetyl- coenzyme A (acetyl Co-A). This process involves the release of one mole of CO2. Later, the acetyl CoA is completely oxidized into CO2 and H2O by entering the citric acid cycle. This pathway follows glycolysis in aerobic organisms and plants. Transformation of Pyruvate into Acetyl-CoA Acetyl CoA can be used in a variety of ways by the cell, but its major function is to deliver the acetyl group derived from pyruvate to the next pathway step, the Citric Acid Cycle. In mitochondria, pyruvate will be transformed into a two-carbon acetyl group (by removing a molecule of carbon dioxide) that will be picked up by a carrier compound called coenzyme A (CoA), which is made from vitamin B5. The resulting compound is called acetyl-CoA and its production is frequently called the oxidation or the transformation of pyruvate 2. Kreb’s Cycle The Krebs cycle or TCA cycle (tricarboxylic acid cycle) or Citric acid cycle is a series of enzyme catalyzed reactions occurring in the mitochondrial matrix, where acetyl-CoA is oxidized to form carbon dioxide and coenzymes are reduced, which generate ATP in the electron transport chain. It is called amphibolic pathway. The amphibolic pathway indicates the one involving both catabolic and anabolic procedures. General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. Step 1: Formation of Citrate Condensation of acetyl CoA with 4-carbon compound oxaloacetate to form 6C citrate, coenzyme A is released. The reaction is catalyzed by citrate synthase. Step 2: Isomerization of Citrate to Isocitrate Citrate is converted to its isomer, isocitrate. In this step, the enzyme aconitase catalyzes the dehydration of citrate to form cis-aconitate. During this dehydration process, a water molecule is used. Aconitate serves as an enzyme-bound intermediate. The enzyme aconitase then catalyzes the conversion of cis-aconitate back to isocitrate. This reaction involves the addition of a water molecule. Step 3: Oxidation of Isocitrate to α-ketoglutarate It is a two-step reaction in which there is first an oxidation, and then a decarboxylation. CO2 is produced, and the electrons are passed to NAD+ to form NADH and H+. Enzyme: Isocitrate dehydrogenase. Step 4: Conversion of α-ketoglutarate to succinyl-CoA Second oxidative decarboxylation reaction occurs. CO2 is released, and succinyl-CoA, NADH, and H+ are produced. Enzyme: Alpha-ketoglutarate dehydrogenase. Step 5: Cleavage of Succinyl-CoA to Succinate Cleavage of the high-energy thioester bond of succinyl- CoA forming succinate. This is coupled with substrate-level phosphorylation of GDP to get GTP. Enzyme: succinate thiokinase (succinyl-CoA synthetase). GTP transfers its phosphate to ADP forming ATP. Step 6: Oxidation of Succinate to Fumarate Succinate is oxidized to fumarate. Succinate transfers two hydrogens together with their electrons to FAD, which forms FADH 2. Enzyme: Succinate dehydrogenase. Step 7: Conversion of Fumarate to Malate Fumarate gets converted to malate by the addition of one H2O. The enzyme catalyzing this reaction is fumarase. Step 8: Oxidation and Regeneration of Malate to Oxaloacetate Malate is dehydrogenated to form oxaloacetate, Hydrogens removed, get transferred to NAD+ forming NADH. Malate dehydrogenase catalyzes the reaction. Product of Kreb’s Cycle Each molecule of acetyl CoA entering the citric acid cycle yields the following: Four CO2 Six NADH Two FADH2 2 GTP 3. Oxidative Phosphorylation Oxidative phosphorylation is the final step in cellular respiration. It occurs in the inner mitochondrial membrane. The electrons are transferred from one member of the transport chain to another through a series of redox reactions. The ETC is responsible for generating a proton gradient across a membrane by using the energy from electron transfer, while chemiosmosis is the process that directly uses this proton gradient to produce ATP. Together, these processes are integral to the generation of ATP in cellular respiration and photosynthesis. Conversion of NADH and FADH2 to ATP General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. Two Reactions in Oxidative Phosphorylation 1. Electron Transport Chain (ETC) A series of protein complexes embedded in the inner mitochondrial membrane. These complexes, labeled I to IV, play a crucial role in oxidative phosphorylation. This movement of electrons releases energy, which is harnessed to pump protons (H+) across the inner mitochondrial membrane, establishing an electrochemical gradient. The Electron Transport Chain (ETC) itself does not directly produce ATP. Instead, the primary function of the ETC is to facilitate the transfer of electrons from electron donors (such as NADH and FADH2) to electron acceptors (such as oxygen) while generating a proton gradient across the inner mitochondrial membrane. Key Steps in Electron Transport Chain A. Delivery of electrons by NADH and FADH2 Reduced electron carriers (NADH and FADH2 from other steps of cellular respiration transfer their electrons to molecules near the beginning of the transport chain. In the process, they turn back into NAD+ and FAD, which can be reused in other steps of cellular respiration. B. Electron transfer and proton pumping. As electrons are passed down the chain, they move from a higher to a lower energy level, releasing energy. Some of the energy is used to pump H+ ions, moving them out of the matrix and into the intermembrane space. This pumping establishes an electrochemical gradient. C. Splitting of oxygen to form water. At the end of the electron transport chain, electrons are transferred to molecular oxygen, which splits in half and takes up H+ to form water. The oxygen is the final electron acceptor in the oxidative phosphorylation D. Gradient-driven synthesis of ATP. As H+ ions flow down their gradient and back into the matrix, they pass through an enzyme called ATP synthase, which harnesses the flow of protons to synthesize ATP. Chemiosmosis Chemiosmosis directly involves the movement of protons (H+ ions) back across the membrane after they have been pumped during the ETC. It harnesses this proton gradient's potential energy to drive the synthesis of ATP. The flow of protons back into the compartment with lower proton concentration is facilitated by the enzyme ATP synthase, which couples this proton flow to ATP production. A proton gradient specifically refers to the electrochemical gradient of protons (H+ ions) across a membrane. General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. Conversion of NADH and FADH2 to ATP The exact conversion of NADH and FADH2 in cellular respiration is not a fixed one-to-one ratio because the production of ATP depends on the specific details of the electron transport chain (ETC) and the proton motive force. However, in very simplified terms, the transfer of electrons from NADH = 2.5 to 3 ATP and FADH2 = 1.5 to 2 ATP C. ROLE OF OXYGEN IN RESPIRATION Most Essential Learning Competency The learners describe the role of oxygen in respiration and describe pathways of electron flow in the absence of oxygen. (STEM_BIO11/12-IIa-j-10) In conditions where the oxygen is insufficient, like in the skeletal muscle cells, the pyruvate cannot be oxidized due to lack of oxygen. Under such conditions, the pyruvate is reduced to lactate by the process of anaerobic glycolysis. Lactic Acid Fermentation Lactic acid fermentation is an anaerobic metabolic process that occurs in cells, particularly in muscle cells during periods of intense exercise or in certain microorganisms. Yogurt and Fermented Foods Lactate production from glucose also occurs in other anaerobic organisms by the process of lactic acid fermentation. The enzyme responsible for catalyzing the conversion of pyruvate to lactic acid is called lactate dehydrogenase. Lactic acid fermentation is commonly observed in certain bacteria, fungi, and human muscle cells. It plays a temporary role in energy production when oxygen is scarce. During strenuous exercise, when oxygen is in short supply, muscle cells may undergo lactic acid fermentation. The accumulation of lactic acid in muscles contributes to muscle fatigue and can lead to temporary discomfort. Alcoholic Fermentation In these processes, bacteria convert sugars into lactic acid, preserving and enhancing the flavor of the food. In some microbes like brewer’s yeast, the pyruvate formed from glucose is converted anaerobically into ethanol and CO2. This is considered the most ancient form of the metabolism of glucose, as observed in conditions where the oxygen concentration is low. The enzyme responsible for catalyzing the conversion of pyruvate to lactic acid is called alcoholic dehydrogenase. Alcoholic fermentation is also involved in the leavening of bread. The carbon dioxide produced during fermentation causes the dough to rise, resulting in a light and airy texture in the final baked product. Besides food and beverage production, alcoholic fermentation is used in various industrial processes, including the production of b Significance of Oxygen 1. Oxygen is the final electron acceptor in the electron transport chain, allowing for the production of ATP. 2. Oxygen is directly involved in the synthesis of ATP from ADP and inorganic phosphate. 3. Oxygen creates a proton gradient across the inner mitochondrial membrane, which is used to drive ATP synthesis. D. ADVANTAGES AND DISADVANTAGES OF FERMENTATION AND AEROBIC RESPIRATION Most Essential Learning Competency The learners explain the advantages and disadvantages of fermentation and aerobic respiration (STEM_BIO11/12-IIa-j-12) COMPARISON DIFFERENCES SIMILARITIES Aerobic Organisms Anaerobic Organisms Fermenting Organisms Aerobic, Anaerobic and Fermenting Organisms Use oxygen. Do not use oxygen. Do not use oxygen. ATP is produced. H2O is the by-product. CO2 is the waste product. General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students.  Electron acceptor is O2 H2 O and potassium Lactate (lactate fermentation) or ethyl Electrons are transferred and is reduced to water. nitrite are the by- alcohol (alcoholic fermentation) is the by- from glucose to NADH. With electron products. product. transport chain. With electron Final acceptors of electrons are pyruvate Occur in prokaryotes transport chain. reduced to lactate, and acetaldehyde reduced and eukaryotes. Electron acceptor is to ethyl alcohol. nitrate or sulfate. No electron transport chain. Occur in prokaryotes. Occur in prokaryotes and eukaryotes. Requires no special Simple and faster alternative to cellular organelles respiration Requires no special organelles Glycolysis and waste product formation are two sets of reactions that occur. ADVANTAGES Aerobic Organisms Anaerobic Organisms Fermenting Organisms All available energy extracted from All available energy All available energy extracted from glucose is 2 ATP. glucose is 36 to 38 ATP. extracted from glucose is Certain bacteria produce chemicals of industrial 39% energy transferred from glucose to 40 ATP (because importance such as isopropanol, butyric acid, acetic acid ATP. prokaryotes have no when bacteria ferment—breakdown of sugars in the Slow breakdown of glucose into ATP. mitochondria). absence of oxygen. Organisms can do more work for a 43% energy transferred Foods that are fermented last longer because these longer time with the slow and efficient from glucose to ATP. fermenting organisms have removed many of the breakdown of ATP. Complete breakdown of nutrients that would attract other microorganisms. Animals and the human muscle cells glucose. Yeasts ferment fruits and wine is produced. Grain is can adapt and perform lactic acid also fermented to produce beer. They also cause the fermentation for a rapid burst of energy. bread to rise due to CO2, a by-product, and alcohol is lost Can breathe heavily to refill the cells in the bread. with oxygen so that lactate is removed Yeasts and lactobacillus together produce sour taste in from the muscle cells. wheat beer. Lactate is returned to the liver to Yeasts and Acetobacter aceti spoil wine to become become pyruvate or glucose again. vinegar. Complete breakdown of glucose. Bacterial fermentation produces yogurt (due to Streptococcus thermophilus and Lactobacillus bulgaricus), sour cream, cheese, brine cucumber pickles, sauerkraut, and kimchi. Clostridium bacteria can produce nail polish remover and rubbing alcohol from the acetone and isopropanol they make Soy sauce is produced by adding mold (Aspergillus), yeasts and fermenting bacteria. DISADVANTAGES Aerobic Organisms Anaerobic Organisms Fermenting Organisms 61% of glucose metabolism becomes 57% of glucose Consumption of 2 ATP is fast. heat and enters the environment. metabolism becomes heat Ethanol and lactate, the by-products of fermentation, Human brain cells cannot perform and enters the have a lot of energy reserves—prokaryotes and lactic acid fermentation. environment. eukaryotes cannot extract the energy in lactate and Human muscle cells feel the burning ethanol using anaerobic method. sensations and pain when lactate Needs a large supply of glucose to perform the same accumulates in the cell and experience work as in aerobic respiration. oxygen debt. Glucose is partially oxidized General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students. References General Biology 1 Teaching Guide https://byjus.com/biology/difference-between-breathing-and-respiration/ https://byjus.com/biology/aerobic-anaerobic-respiration/ https://www.diffen.com/difference/Aerobic_Respiration_vs_Anaerobic_Respiration https://www.biologyonline.com/dictionary/cellular-respiration https://microbenotes.com/glycolysis/ https://bio.libretexts.org/Bookshelves/Human_Biology/Human_Biology_(Wakim_and_Grewal)/05%3A_Cells/5.09%3A_Cellular_Respiration https://byjus.com/neet/krebs-cycle/#:~:text=Also%20known%20as%20the%20citric,ADP%20is%20converted%20into%20ATP. https://microbenotes.com/oxidative-phosphorylation/ https://www.khanacademy.org/science/ap-biology/cellular-energetics/cellular-respiration-ap/a/oxidative-phosphorylation-etc General Biology 1 Lecture – Photosynthesis Prepared for Bauan Technical Integrated High School Grade 11 STEM students.