Science Reviewer (Juris Bibar) Cellular Respiration PDF

SCIENCE REVIEWER (JURIS BIBAR) I. What is Glycolysis? Glyco means relating to sugar Lysis is the breaking down of molecules Glycolysis is the breakdown of Glucose(sugar molecules), which is a 6-carbon molecule, into 2 molecules of pyruvic acid or pyruvate, a 3-carbon molecu...

SCIENCE REVIEWER (JURIS BIBAR) I. What is Glycolysis? Glyco means relating to sugar Lysis is the breaking down of molecules Glycolysis is the breakdown of Glucose(sugar molecules), which is a 6-carbon molecule, into 2 molecules of pyruvic acid or pyruvate, a 3-carbon molecule. Glucose Pyruvate C6H12O6 -> CH3COCOOH Glycolysis is a metabolic pathway that converts glucose into energy and intermediates for other metabolic pathways. It doesn’t require oxygen, making it an anaerobic process, although whether or not it involves oxygen dictates the outcome of its byproduct (pyruvate) It’s the first step in cellular respiration, preceding the Krebs Cycle and ETC Glycolysis takes place in the Cytoplasm of the cell. With oxygen involved, the pyruvate will be used in the Krebs Cycle With no oxygen, the pyruvate will be turned into lactate II. Inputs > One glucose, 2 ATP, and 2 NADP+ III. Outputs > Two pyruvate, 2 ADP, and 2 NADH IV. Process Phosphorylation (Hexokinase)  > Glucose is Phosphorylated in the presence of hexokinase to produce Glucose-6-phosphate. In this step, an ATP molecule is converted to ADP, and one inorganic phosphate is added to the 6th position C-atom. > Phosphorylation is the process of adding a Phosphate group into a molecule or compound > e.g., ADP becoming ATP (Extra Phosphate is added) Isomerization (Phosphoglucose isomerase) > The Glucose-6-phosphate is then isomerized to Fructose-6-phosphate in the presence of phosphoglucose isomerase. > To isomerize is to convert from one isomer to another. Isomers are groups of atoms with the same formula but different structures, like Glucose (C6H12O6) and Fructose (C6H12O6) Phosphorylation (phosphofructokinase) > Another ATP molecule is used, and one inorganic phosphate is added to the 1st C-atom, producing Fructose-1,6-Bisphosphate from the Fructose 6 Phosphate. > The phosphorylation was caused by Phosphofructokinase. Splitting (Aldolase) > The 6 C-molecule, Fructose-1,6-Bisphosphate, is split into two 3-carbon isomers - Dihydroxyacetone phosphate and Glyceraldehyde-3-phosphate. > The production of the two isomers is caused by aldolase. Isomerization (Triose Phosphate Isomerase) > Dihydroxyacetone phosphate is isomerized to glyceraldehyde-3-phosphate in the presence of the triosephosphate isomerase enzyme. Dehydration  > In this step, a dehydrogenase enzyme is used, and the Glyceraldehyde-2-Phosphate is oxidized (combined with oxygen) and phosphorylated (added Phosphate) to 1,3-Bisphosphoglyceric acid. The source of the inorganic phosphate here is NADPH. Oxidative Phosphorylation > The phosphate group from the carboxylic group is transferred to an ADP or Adenosine Diphosphate molecule, and hence an ATP molecule is produced. The reaction is catalyzed by phosphoglycerate kinase. The resulting molecule is 3-Phosphoglyceric acid. Transfer of Phosphate Group (Phosphoglycerate mutase)8 > The phosphate group is shifted to the 2nd carbon atom, producing 2-Phosphoglyceric acid using the enzyme Phosphoglycerate mutase. Dehydration (enolase) > 2-Phosphoglyceric acid is dehydrated to produce Phosphoenolpyruvate in the presence of enolase. Transfer of phosphate group ( Pyruvate Kinase) > The final step of Glycolysis is the production of another ATP molecule where the phosphate group is transferred from phosphoenolpyruvate to an ADP molecule. The reaction is catalyzed by pyruvate kinase and produces pyruvate. The two phosphorylation reactions are also called priming reactions since they 'activate' the molecules for the subsequent reactions. Kreb Cycle (aka Citric Acid Cycle or TCA Cycle): 1. Introduction: ○ Cellular respiration occurs in the mitochondria to break down glucose and oxygen, producing ATP. ○ It happens in the cytoplasm and mitochondrial matrix of eukaryotic cells. 2. Mitochondrial Matrix:  ○ Gel-like space inside the inner membrane of mitochondria. 3. Purpose: ○ Production of amino acids. ○ Formation of NADH and ATP for energy and synthetic processes. 4. Raw Materials: ○ Acetyl-CoA (from pyruvate, fatty acids, or amino acids). ○ Oxaloacetate. ○ NAD+ and FAD (electron acceptors). ○ ADP and inorganic phosphate (for ATP generation). 5. Steps in the Cycle: ○ Citrate Synthase: Combines oxaloacetate and acetyl-CoA to form citrate/citric acid. ○ Aconitase: Converts citrate to isocitrate/isocitric acid. ○ Isocitrate Dehydrogenase: Oxidizes isocitrate to alpha-ketoglutaric acid, releasing 1 CO2 and forming NADH. ○ Alpha-Ketoglutarate Dehydrogenase: Converts alpha-ketoglutaric acid to succinyl-CoA releasing 1 CO2 and forming NADH. ○ Succinyl-CoA Synthase: Converts succinyl-CoA to succinate, producing ATP or GTP. ○ Succinate Dehydrogenase: Oxidizes succinate to fumarate, generating FADH2. ○ Fumarase: Converts fumarate to malate. ○ Malate Dehydrogenase: Oxidizes malate to oxaloacetate, producing NADH. 6. Products (Per Acetyl-CoA): ○ 3 NADH. ○ 1 FADH2. ○ 1 GTP (or ATP). ○ 2 CO2 (as waste). 7. Products (Overall, Per Glucose Molecule): ○ 6 NADH. ○ 2 FADH2. ○ 2 GTP (or ATP). ○ 4 CO2 (as waste). Electron Transport Chain (ETC) Objective: To couple the energy stored in electron acceptors to a proton gradient, driving ATP synthesis. Key Structures Involved: 1. Intermembrane Space ○ Region where protons accumulate during the process. 2. Inner Mitochondrial Membrane ○ Location of the ETC and ATP synthase. 3. Mitochondrial Matrix ○ Source of NADH and FADH2, key electron donors. The Electron Transport Chain (ETC) is the final stage of cellular respiration. It is responsible for generating most of the cell's ATP by harnessing the energy released as electrons are transferred through a series of protein complexes embedded in the inner mitochondrial membrane. Step 1: Electron Donation NADH and FADH2, generated in earlier stages of cellular respiration (glycolysis, Krebs cycle), donate electrons to the ETC. ○ NADH donates electrons to Complex I. ○ FADH2 donates electrons to Complex II (bypassing Complex I).  Step 2: Electron Transport and Proton Pumping 1. Complex I (NADH Dehydrogenase): ○ Accepts electrons from NADH. ○ Transfers these electrons to Coenzyme Q (CoQ). ○ Pumps protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating a proton gradient. 2. Complex II (Succinate Dehydrogenase): ○ Accepts electrons from FADH2. ○ Passes these electrons to Coenzyme Q without pumping protons. 3. Coenzyme Q (CoQ): ○ A mobile electron carrier that transfers electrons from Complexes I and II to Complex III. 4. Complex III (Cytochrome bc1 Complex): ○ Accepts electrons from CoQ. ○ Transfers them to Cytochrome C, another mobile carrier. ○ Pumps more protons into the intermembrane space. 5. Cytochrome C: ○ Shuttles electrons from Complex III to Complex IV. 6. Complex IV (Cytochrome C Oxidase): ○ Transfers electrons to oxygen, the final electron acceptor. ○ Oxygen combines with electrons and protons to form water (H₂O). ○ Pumps additional protons into the intermembrane space. Step 3: Formation of a Proton Gradient The electron transfer process pumps protons (H⁺) from the mitochondrial matrix into the intermembrane space, creating a proton gradient (higher proton concentration in the intermembrane space than in the matrix). Step 4: ATP Synthesis via Chemiosmosis 1. The proton gradient generates a potential energy difference across the inner mitochondrial membrane, known as the proton-motive force. 2. ATP Synthase, a protein complex, provides a channel for protons to flow back into the matrix. 3. As protons pass through ATP Synthase, the energy released drives the conversion of ADP (adenosine diphosphate) and inorganic phosphate (Pi) into ATP. Inhibitors and Uncouplers: Chemicals like antimycin, rotenone, cyanide, and oligomycin can interfere with the ETC or ATP synthesis. Key Products 1. Each NADH produces approximately 2.5 ATP. 2. Each FADH2 produces approximately 1.5 ATP. 3. Water is formed as oxygen accepts electrons and protons.