5415 Metabolism (2024-2025, 1st Semester) PDF

Metabolism 5415 SY [ 5415 ] : BIOCHEMISTRY LEC...

Metabolism 5415 SY [ 5415 ] : BIOCHEMISTRY LEC 2024-2025 Mr. CHRISTIAN M. SANUCO, RMT 1ST SEMESTER METABOLIC MAP MEMBERS Different pathways can intersect, forming an BANGA, MICHAEL LEWIS integrated and purposeful network of chemical BARTOLOME, MHARINIEL D. reactions, The Metabolic Map. BATO, JANINE ASHLEY B. The metabolic map shows how all pathways JASMIN, CHARISSA MAE DS. come together, it helps us understand the effect LUMAUIG, SHYRINE KATE SERAFICA, VINCE MANUEL A. of each path on the entire metabolism. TAMANI, PRINCESS KHARYLLE MHEI B. VERCIDA, JORENCE D. VILLANUEVA, MARJIE FLOUSE VITANZOS, PRINCESS JUSELLE T. METABOLISM Metabolism is the sum total of all the reactions that take place in a living cell. These reactions are used to extract energy and materials from the environment (catabolism) and to use thus energy and these materials to produce new molecules (anabolism) that will sustain the cell and allow it to propagate itself. Every chemical reaction in metabolism is catalyzed by an enzyme. An outside source of energy is needed to drive metabolism Normal metabolism is vital for health, growth, reproduction, and good survival of human beings. METABOLIC ROADMAP Metabolic Pathways METABOLISM AND CELL STRUCTURE ○ Series of interconnected biochemical reactions that convert a substrate molecule or Metabolism refers to the entire set of chemical molecules, step-by-step, through a series of reactions that occur in a cell to sustain life and It metabolic intermediates, eventually yielding a is tightly linked to the cell's structural final product or products. components, which provide specific Composed of two types: compartments These reactions are organized into metabolic pathways that can be classified into: Catabolism: Breaking down molecules to release energy. Anabolism: Building complex molecules from simpler ones, requiring energy. CELL STRUCTURE CYTOPLASM ‘Site of the Glycolysis’ The process by which glucose is broken down into pyruvate (ATP and NADH) It is the initial steps of lipid and protein synthesis GROUP 5 | BSMLS 2A 1  METABOLISM MITOCHONDRIA ‘Powerhouses of the cell’ - It is primary sites for aerobic respiration The Citric Acid Cycle, Oxidative Phosphorylation and Fatty Acid Oxidation occurs and producing ATP, the main energy currency of the cell. ENDOPLASMIC RETICULUM Contributes to detoxification processes and calcium ion storage Rough ER: for protein synthesis Smooth ER: involved in lipid and steroid synthesis LYSOSOME AND PEROXISOMES Flavin Adenine Dinucleotide (FAD) A coenzyme required in numerous metabolic These are involved in the breakdown of redox macromolecules and detoxification of reactive CH, CH, oxygen. reactions FAD is oxidized form PLASMA MEMBRANE FADH, is reduced form In enzyme reactions FAD goes Transport proteins and signaling molecules in back and forth (equilibrium) from oxidized to reduced membrane for energy metabolism that is form. required for metabolic reactions. Flavin A typical cellular reaction in which FAD serves as IMPORTANT NUCLEOTIDE-CONTAINING oxidizing agent involves conversion of an alkane to an alkene COMPOUNDS Adenosine Phosphates (ATP, ADP and AMP) AMP: Structural component of RNA ADP and ATP: Key components of metabolic pathways Phosphate groups are connected to AMP by strained bonds which require 0 0 less than normal energy to hydrolyze 0-p-0-p-o-p-0-cH, o them ATP + H,O > ADP + PO,3- + ОН ОН Energy ADP + H2O - AMP + PO 3- + Adenosine monophosphate (AMP) Energy Nicotinamide Adenine Dinucleotide (NAD) Y NAD*: coenzyme Adenosine diphosphate (ADP) NADH is reduced form Overall Reaction: ATP + 2H,0 + AMP + 2 3 Subunit structure: PO 3- + Energy - Nicotinamide - ribose - ADP Adenosine triphosphate (ATP) - 6 Subunit structure: The net energy produced in these reactions is used Nicotinamide -- ribose for cellular reactions -phosphate --phosphate - ribose - adenine e.g., conversion of glucose to glucose-6-phosphate A typical cellular reaction in which NAD+ serves as the oxidizing agent is the oxidation of a secondary alcohol to give a ketone. GROUP 5 | BSMLS 2A 2  METABOLISM 2. Oxaloacetate (C₄H₄O₅²⁻) Oxaloacetate is a key intermediate in the citric acid cycle. It condenses with acetyl-CoA to form citrate and also participates in gluconeogenesis as a precursor for glucose synthesis. 3. Citrate (C₆H₅O₇³⁻) Citrate is the first intermediate in the citric acid cycle. It is formed by the condensation of oxaloacetate and acetyl-CoA and is involved in the regulation of glycolysis through feedback inhibition. 4. α-Ketoglutarate (C₅H₄O₅²⁻) α-Ketoglutarate is an intermediate in the citric acid cycle and is also involved in amino acid metabolism, serving as a precursor for glutamate synthesis. Coenzyme A 5. Malate (C₄H₄O₅²⁻) A derivative of vitamin B Malate is another intermediate in the citric acid Active form of coenzyme A is the sulfhydryl group cycle. It is involved in the malate-aspartate (-SH group) in the ethanethiol subunit of the coenzyme shuttle, which transports reducing equivalents Acetyl-CoA (acetylated) across mitochondrial membranes. 6. Succinate (C₄H₄O₄²⁻) Succinate is a citric acid cycle intermediate that participates in the electron transport chain as a substrate for succinate dehydrogenase. Classification of Metabolic Intermediate Compounds 7. Fumarate (C₄H₂O₄²⁻) Metabolic intermediate compounds can be Fumarate is an intermediate in the citric acid classified into three groups based on their cycle and urea cycle, contributing to both energy functions metabolism and nitrogen elimination. HIGH-ENERGY PHOSPHATE COMPOUNDS High energy phosphate refers to compounds containing phosphate ester bonds that play a crucial role in transferring chemical energy within the body. 1. ATP ➔ ATP (Adenosine Triphosphate) contains high energy bonds located between each phosphate group. These bonds are known as IMPORTANT CARBOXYLATE IONS IN METABOLIC phosphoric anhydride bonds. ➔ There are three reasons these bonds are high PATHWAYS energy. 1. Pyruvate (C₃H₃O₃⁻) a. The electrostatic repulsion of the positively charged phosphates and Pyruvate is the end product of glycolysis. It negatively charged oxygen stabilizes serves as a critical intersection in metabolic the products (ADP + Pi) of breaking pathways, converting into acetyl-CoA for entry these bonds. into the citric acid cycle under aerobic conditions b. The stabilization of products by or into lactate during anaerobic metabolism. ionization and resonance. As the GROUP 5 | BSMLS 2A 3  METABOLISM bonds are broken there is an units—which occurs in the mouth, stomach, increased stability due to the and small intestine. resonance of that product's structure. ○ Additionally, the first metabolic pathway c. The entropy increases. There is a synthesizes sugar from smaller molecules, and greater stability in the products the other pathway breaks sugar into smaller because there exists a greater molecules. entropy; i.e more randomness. 1 mole ○ The Process: of reactants has a higher energy than ○ Begins in the mouth (amylase) 2 moles of products. Disorder is ○ Continues to stomach (gastric juices) favored over order according to the ○ Completed in small intestine 2nd law of thermodynamics. ○ The end product is glucose. monosaccharides, amino acids, fatty acids & glycerol 2. ADP ○ Once they are in the blood, they will then be ➔ ADP (Adenosine Diphosphate) also contains distributed to cells in various body parts. high energy bonds located between each Stage 2: Acetyl Group Formation phosphate group. It has the same structure as ○ Occurs in cytosol and mitochondria ATP, with one less phosphate group. ○ Small molecules from digestion are then 3. NAD + oxidized ➔ NAD + (Nicotinamide adenine dinucleotide ○ Primary products are 2-carbon Acetyl units (oxidized form)) is a crucial electron acceptor (attached to coenzyme A to give acetyl CoA) in a catabolic reactions, oxidizing alcohol and then reduced coenzyme NADH groups to carbonyl groups, and is essential for ○ These monomer units (or building blocks) are metabolic processes like beta-oxidation, further broken down through different reaction glycolysis and TCA cycle. pathways, one of which produces ATP to form a common end product, Acetyl-coenzyme A, 4. NADH that can then be used in stage III to produce ➔ NADH (reduced form) is an NAD+ that has even more ATP accepted electrons in the form of hydride ions. Stage 3: Citric Acid Cycle NADH is also one of the molecules ○ Occurs inside mitochondria responsible for donating electrons to the ETC ○ Acetyl groups are oxidized to produce CO2 to drive oxidative phosphorylation and also and energy pyruvate during fermentation processes. ○ Some of the energy released is lost as heat 5. NADP + ○ Some carry by reduced coenzymes NADH ➔ NADP+ (Nicotinamide adenine dinucleotide and FADH to the fourth stage phosphate (oxidized form)) is the major ○ Exhaled CO2 comes primarily from this stage electron donor for anabolic reactions. Stage 4: Electron Transport Chain and Oxidative Phosphorylation 6. NADPH ○ Occurs inside mitochondria ➔ Nicotinamide adenine dinucleotide phosphate (reduced form). ○ NADH and FADH2 supply the fuel needed for the production of ATP molecules OVERVIEW OF BIOCHEMICAL ENERGY ○ Oxygen gas is converted to water. Biochemical energy production in metabolism CITRIC ACID CYCLE refers to the processes through which cells convert nutrients into usable forms of energy, Also known as TCA (Tricarboxylic Acid Cycle) primarily in the form of adenosine triphosphate and the famous Kreb’s Cycle. (ATP). Occurs within a cellular organelle, the mitochondria. FOUR STAGES OF BIOCHEMICAL ENERGY Utilizes about two-thirds of the total Oxygen consumed by the body. Stage 1: Digestion It is strictly aerobic in contrast to glycolysis. ○ In stage I, carbohydrates, fats, and proteins are ○ The Cycle: broken down into monomer units: The first step in complete oxidation is the carbohydrates into simple sugars, fats into fatty decarboxylation of pyruvate to produce acids and glycerol, and proteins into amino acetyl-CoA. acids. One part of stage I of catabolism is the ○ The end product of glycolysis, Pyruvate, is breakdown of food molecules by hydrolysis transported into the mitochondria and loses reactions into the individual monomer CO2 to form acetyl-CoA. GROUP 5 | BSMLS 2A 4  METABOLISM The second regulatory site is the isocitrate dehydrogenase reaction. In this case, ADP and NAD+ are allosteric activators of the enzyme. We have called attention to the recurring pattern in When the acetyl-CoA is fed into the Cycle which ATP and NADH inhibit enzymes of the where its two Carbons are oxidized to CO2, pathway, and ADP and NAD+ activate these chemical energy is released in the form of 3 enzymes. NADH, 1 FADH2, AND 1 ATP. The α-ketoglutarate dehydrogenase complex is ○ In the process: the third regulatory site. As before, ATP and 3 NAD+ is reduced to NADH are inhibitors. Succinyl-CoA is also an NADH/H+ inhibitor of this reaction. This recurring theme in 1 FAD is reduced to FADH2 metabolism reflects the way in which a cell can 1 GDP is phosphorylated to adjust to an active state or to a resting state. GTP In summary, four control points exist for the citric acid cycle. One, the pyruvate dehydrogenase However, since the end product of Glycolysis reaction, lies outside the cycle proper. The is 2 Pyruvates and the Cycle circles twice, formation of citrate and the two oxidative products should be multiplied by two (2x). decarboxylations are the other control points. ATP The cycle starts and ends with Oxaloacetate. and NADH are inhibitors of the cycle, and ADP and NAD+ are activators. CONTROL OF THE CITRIC ACID CYCLE When the four NADH and single FADH2 produced by the pyruvate dehydrogenase complex and citric acid cycle are reoxidized by ELECTRON TRANSPORT CHAIN the electron transport chain, considerable quantities of ATP are produced. Control of the Located in the inner mitochondrial membrane. citric acid cycle is exercised at three points; three Carries the reoxidation of the NADH/H+ to NAD enzymes within the citric acid cycle play a and FADH2 to FAD using molecular oxygen as regulatory role. the oxidizing agent. There is also control of access to the cycle via pyruvate dehydrogenase. Protein Complexes The end products of a series of reactions inhibit ○ Comlex I (NADH Dehydrogenase): Accepts the first reaction, and the intermediate reactions electrons from NADH, converting it back to do not occur when their products are not needed. NAD+. This complex pumps protons (H+) The pyruvate dehydrogenase (PDH) complex is from the mitochondrial matrix into the activated by ADP, which is abundant when a cell intermembrane space, contributing to the needs energy. In mammals, the actual proton gradient. mechanism by which the inhibition takes place is ○ Complex II (Succinate Dehydrogenase): the phosphorylation of pyruvate dehydrogenase. Accepts electrons from FADH2, which is Within the citric acid cycle itself, the three control produced in the Krebs cycle. Unlike Complex points are the reactions catalyzed by citrate I, it does not pump protons. synthase, isocitrate dehydrogenase, and the α-ketoglutarate dehydrogenase complex. ○ Complex III (Cytochrome bc1 Complex): We have already mentioned that the first reaction Receives electrons from ubiquinone and of the cycle is one in which regulatory control pumps more protons into the intermembrane appears, as is to be expected in the first reaction space. of any pathway. Citrate synthase is an allosteric ○ Complex IV (Cytochrome c Oxidase): enzyme inhibited by ATP, NADH, succinyl-CoA, Accepts electrons from cytochrome c and and its product, citrate. transfers them to oxygen, the final electron acceptor, forming water. This complex also GROUP 5 | BSMLS 2A 5  METABOLISM pumps protons into the intermembrane ○ A net gain of 2 ATP molecules is produced space. directly from glycolysis. The energy released in the reoxidation is coupled ○ Additionally, 2 NADH molecules are to the synthesis of ATP from ADP and Pi by the generated, which can further contribute to ATP production in the mitochondria during enzyme ATP synthase. oxidative phosphorylation. The coupling involves the creation of a hydrogen ion concentration gradient across the inner mitochondrial membrane. OXIDATIVE PHOSPHORYLATION Oxidative phosphorylation refers to the process of synthesizing ATP using the energy stored in the proton gradient created by the ETC. ATP Synthase ○ The enzyme responsible for this process is called ATP synthase, which is also located in the inner mitochondrial membrane. KREBS CYCLE ○ Proton Flow: Protons flow back into Location: Mitochondrial matrix the mitochondrial matrix through ATP Process: Each pyruvate from glycolysis is synthase due to the concentration converted into acetyl-CoA before entering the gradient. ○ ATP Production: As protons pass Krebs cycle. This cycle involves a series of through ATP synthase, it rotates and reactions that oxidize acetyl-CoA to produce catalyzes the conversion of ADP CO2 while transferring high-energy electrons (adenosine diphosphate) and to carrier molecules NADH and FADH2. inorganic phosphate (Pi) into ATP ATP Yield: (adenosine triphosphate). Each turn of the cycle produces 1 ATP directly (or GTP, which can be converted to ATP). ATP PRODUCTION FOR THE COMMON For each glucose molecule, which METABOLIC PATHWAYS yields two acetyl-CoA molecules, the cycle turns twice, resulting in a total of 2 ATP per glucose. Adenosine triphosphate (ATP) is the primary energy carrier in cells, produced through various Additionally, 6 NADH and 2 FADH2 metabolic pathways that convert energy stored in are produced per glucose molecule nutrients into usable forms. The main pathways for ATP production include glycolysis, the Krebs cycle (also known as the citric acid cycle), and oxidative phosphorylation via the electron transport chain (ETC). Understanding these pathways is crucial for grasping how cells generate energy to support life processes. GLYCOLYSIS Location: Cytoplasm Process: Glycolysis is the initial stage of glucose metabolism, where one molecule of glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (three carbons each). This process occurs in a series of ten OXIDATIVE PHOSPHORYLATION enzyme-catalyzed reactions. ATP Yield: Location: Inner mitochondrial membrane GROUP 5 | BSMLS 2A 6  METABOLISM Process: The NADH and FADH2 generated the initial step in both aerobic from glycolysis and the Krebs cycle donate and anaerobic respiration. electrons to the ETC. As electrons move Takes place in the cytoplasm through a series of protein complexes, protons and involves the breakdown of are pumped across the membrane, creating a glucose into two molecules of proton gradient. This gradient drives protons pyruvate. back through ATP synthase, leading to the During glycolysis, a small synthesis of ATP. amount of ATP is produced, ATP Yield: and NADH (nicotinamide Approximately 3 ATP are produced for adenine dinucleotide) is each NADH oxidized and about 2 ATP generated as a reducing for each FADH2 oxidized. agent. In total, oxidative phosphorylation can Oxygen is not directly involved yield about 26 to 28 ATP per glucose in glycolysis, but it is required molecule for the subsequent steps of aerobic respiration. ○ Fermentation occurs in the absence of oxygen and an alternative pathway for ATP production It involves the conversion of pyruvate into either lactate or ethanol, depending on the organism. Fermentation regenerates NAD+ (oxidized form of NADH) from NADH, allowing glycolysis to continue in the absence of oxygen. TOTAL ATP PRODUCTION Fermentation does not When combining all phases of cellular respiration: produce as much ATP as aerobic respiration, it is crucial Glycolysis: 2 ATP for organisms that cannot Krebs Cycle: 2 ATP survive in oxygen-rich Oxidative Phosphorylation: Approximately 26 environments. to 28 ATP >90% of inhaled oxygen via respiration is consumed during oxidative phosphorylation. This results in a total yield of approximately 30 to 32 Remaining O, are converted to several highly ATP molecules per glucose molecule, depending on reactive oxygen species (ROS) with in the the efficiency of the electron transport chain and other body. cellular conditions Examples of ROS: NON-ETC OXYGEN-CONSUMING REACTIONS ○ Hydrogen peroxide (H,O.) ○ Superoxide ion (O,) Refers to the metabolic processes that do not ○ Hydroxyl radical (OH) directly involve the ETC in cellular respiration ROS can also be formed due to external These reactions occur in the cytoplasm and influences such as polluted air, cigarette are essential for the production of ATP, the smoke, and radiation exposure energy currency of cells ROS are both beneficial as well a problematic Example of a non-ETC oxygen-consuming within the body reaction Beneficial Example: White blood cells produce ○ Glycolysis a significant amount of superoxide free GROUP 5 | BSMLS 2A 7  METABOLISM radicals via the following reaction to destroy Antioxidants present in the body: the invading bacteria and viruses. ○ Vitamin K ○ Vitamin C ○ Glutathione (GSH) > 95% of the ROS formed are quickly ○ Beta-carotene converted to non toxic species: Plant products such as flavonoids are also good antioxidants - Have shown promise in the management of many disorders associated with ROS production About 5% of ROS escape destruction by superoxide dismutase and catalase enzymes. Antioxidant molecules present in the body help trap ROS species B VITAMINS AND THE COMMON METABOLIC can further be used in aerobic or anaerobic PATHWAYS pathways. Common Metabolic Pathways 2. Citric Acid Cycle (Krebs Cycle, TCA Cycle) 1. Glycolysis Purpose: The citric acid cycle processes acetyl-CoA (derived from carbohydrates, fats, Purpose: Glycolysis is the breakdown of and proteins) into carbon dioxide and glucose (a six-carbon sugar) into two high-energy electron carriers (NADH, FADH2). molecules of pyruvate (a three-carbon Location: Mitochondria. compound), producing ATP and NADH in the Key Steps: process. ○ Acetyl-CoA enters the cycle and Location: Cytoplasm of the cell. combines with oxaloacetate to form Key Steps: citrate. ○ Glucose is phosphorylated to ○ Through a series of steps, citrate is glucose-6-phosphate. oxidized, releasing CO2 and ○ ATP is produced by substrate-level generating NADH and FADH2. phosphorylation. ○ ATP is produced by substrate-level ○ NADH is generated through the phosphorylation. reduction of NAD+. ○ The cycle regenerates oxaloacetate to ○ Ends with the formation of pyruvate. continue the process. Importance: Provides energy quickly without Importance: Key step in aerobic respiration, it the need for oxygen (anaerobic). The pyruvate provides energy and intermediates for other metabolic pathways. GROUP 5 | BSMLS 2A 8  METABOLISM 3. Oxidative Phosphorylation (Electron Transport Key Steps: Chain and Chemiosmosis) ○ Fatty acids are first activated and then enter the mitochondria. Purpose: To produce ATP through the transfer ○ In the mitochondria, fatty acids are of electrons from NADH and FADH2 to oxygen broken down in cycles, removing in the mitochondria. two-carbon units at a time to form Location: Mitochondrial inner membrane. acetyl-CoA. Key Steps: ○ Each cycle produces NADH and ○ Electrons from NADH and FADH2 FADH2. pass through a series of protein Importance: A major pathway for energy complexes (ETC). production from fats, especially during periods ○ Energy from electrons is used to of fasting or prolonged exercise. pump protons (H+) across the membrane, creating an 6. Gluconeogenesis electrochemical gradient. ○ Protons flow back through ATP Purpose: The process of synthesizing glucose synthase, driving the synthesis of ATP. from non-carbohydrate precursors like lactate, ○ Oxygen acts as the final electron glycerol, and amino acids. acceptor, combining with electrons Location: Primarily in the liver (and to a lesser and protons to form water. extent, in the kidneys). Importance: The main pathway for ATP Key Steps: production in cells with oxygen (aerobic ○ Non-carbohydrate substrates are conditions). converted into intermediates that can be used to generate glucose. 4. Fermentation ○ Key enzymes bypass the steps of glycolysis that are irreversible (e.g., Purpose: When oxygen is not available pyruvate carboxylase and (anaerobic conditions), fermentation allows phosphoenolpyruvate carboxykinase). glycolysis to continue by regenerating NAD+ Importance: Essential for maintaining blood from NADH, producing small amounts of ATP. glucose levels, especially during fasting or Location: Cytoplasm. prolonged exercise. Key Steps: ○ In the absence of oxygen, pyruvate 7. Pentose Phosphate Pathway (PPP) from glycolysis is converted into either lactate (lactic acid fermentation) or Purpose: To generate NADPH (used in ethanol and CO2 (alcoholic anabolic reactions) and ribose-5-phosphate fermentation). (used in nucleotide synthesis). ○ This process regenerates NAD+, Location: Cytoplasm. allowing glycolysis to continue. Key Steps: Importance: Provides energy in the absence ○ Glucose-6-phosphate is oxidized to of oxygen but is less efficient than oxidative produce NADPH and phosphorylation. ribose-5-phosphate. ○ The pathway also generates 5. Beta-Oxidation (Fatty Acid Metabolism) intermediates that can enter glycolysis. Purpose: The breakdown of fatty acids into Importance: Provides reducing power for acetyl-CoA units, which can then enter the biosynthetic processes, such as fatty acid and citric acid cycle. nucleotide synthesis. Location: Mitochondria (and peroxisomes for longer fatty acids). 8. Urea Cycle (Ornithine Cycle) GROUP 5 | BSMLS 2A 9  METABOLISM Purpose: The urea cycle detoxifies ammonia, Importance: Cholesterol is a key component a byproduct of protein metabolism, by of cell membranes and precursor to steroid converting it into urea, which can be excreted hormones, bile acids, and vitamin D. in urine. Location: Liver (with some steps in the B VITAMINS mitochondria and others in the cytoplasm). Key Steps: The B vitamins comprise a group of eight ○ Ammonia is combined with carbon water-soluble vitamins (B1, B2, B3, B5, B6, B7, B9, dioxide to form carbamoyl phosphate, and B12) that act as cofactors, precursors, and which then enters the cycle. substrates for numerous biological processes. Dietary ○ Through several steps, ammonia is intake of these B vitamins is essential for the eventually converted into urea, which maintenance of human health and deficiencies can is excreted by the kidneys. have severe health consequences. Almost all of the B Importance: Prevents the accumulation of vitamins are either directly or tangentially involved in toxic ammonia and helps maintain nitrogen one-carbon metabolism. balance. Biological Function and Metabolic Pathways 9. Amino Acid Metabolism 1.B1 (thiamine) Purpose: The breakdown and synthesis of Cofactor for enzymes in glucose metabolism, amino amino acids, which are the building blocks of acid catabolism, nucleotide synthesis, and fatty acid proteins. synthesis. Location: Various, depending on the specific amino acid. Pathway: Thiamine is involved in the pyruvate Key Steps: dehydrogenase complex (PDC) and the citric acid ○ Amino acids are deaminated (removal cycle (Krebs cycle), which are key parts of cellular of the amino group), producing respiration. ammonia and carbon skeletons. ○ The carbon skeletons can be 2.B2 (riboflavin) converted into intermediates of the citric acid cycle or used for Precursor for flavin mononucleotide (FMN) and flavin gluconeogenesis or lipogenesis. adenine dinucleotide (FAD) for cellular respiration. Importance: Essential for protein synthesis, energy production, and maintaining nitrogen Pathway: Riboflavin plays a key role in the electron balance. transport chain (ETC), helping produce ATP through oxidative phosphorylation by accepting electrons in 10. Cholesterol Metabolism the form of FADH2. Purpose: Synthesis of cholesterol from 3. B3 (nicotinamide) acetyl-CoA, which is important for the formation of cell membranes, hormones, and Precursor for nicotinamide adenine dinucleotide bile acids. (NAD) utilized in biosynthetic pathways, energy Location: Cytoplasm and smooth metabolism, and protection from reactive oxygen endoplasmic reticulum. species. Key Steps: Pathway: NAD+ is a key electron carrier in ○ Acetyl-CoA is converted into glycolysis, the citric acid cycle, and the electron mevalonate, a precursor for transport chain, all of which are involved in energy cholesterol. production. ○ Cholesterol is synthesized via several enzyme-mediated steps. GROUP 5 | BSMLS 2A 10  METABOLISM 4. B5 (pantothenic acid) REFERENCES Precursor for coenzyme A (coA), an acyl-carrier Cooper, G. M. (2000). The Mechanism of Oxidative required for the activity of many enzymes. Phosphorylation. The Cell - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK9885/ Pathway: CoA is essential for the acetyl-CoA Harvey, R. A., & Ferrier, D. R. (2010). Lippincott's illustrated formation, which enters the citric acid cycle. It is also reviews: Biochemistry (5th ed.). Lippincott Williams & involved in fatty acid oxidation and the synthesis of Wilkins. steroid hormones. Libretexts. (2022). Important high energy molecules in metabolism. Chemistry LibreTexts. 5. B6 (pyridoxine) Libretexts. (2024, November 23). 7.11: Oxidative Cofactor for over 150 enzymes involved mainly in Phosphorylation - Electron Transport Chain. Biology amino acid synthesis and degradation. LibreTexts. https://bio.libretexts.org/Bookshelves/Introductory_and_Ge neral_Biology/General_Biology_(Boundless)/07:_Cellular_Re Pathway: Vitamin B6 is essential for glycogen spiration/7.11:_Oxidative_Phosphorylation_-_Electron_Trans metabolism and is involved in the conversion of port_Chain glutamate to gamma-aminobutyric acid (GABA). It also plays a role in the breakdown of amino acids for Bettelheim, F. A., Brown, W. H., Campbell, M. K., Farrell, S. O., & Torres, O. (2019). Introduction to general, organic, and gluconeogenesis. biochemistry (11th ed.). Cengage Learning. 6. B7 (biotin) P.A. Kennedy, (2019) B Vitamins and One-Carbon Metabolism: Implications in Human Health and Plays an essential role in carboxylation reactions and Diseasehttps://pmc.ncbi.nlm.nih.gov/articles/PMC7551072/ ?fbclid=IwY2xjawGzT3JleHRuA2FlbQIxMAABHVJABI5Txsq also has many applications in laboratory research ylwxlBE5TCwAuXl-1qAAJCef3FR2-KFRe90FKeMTuPakUvg _aem_Zom3WJ9fObs5nuTa6r_SWw#:~:text=Vitamins%20B Pathway: Biotin is crucial for fatty acid synthesis, 9%20(folate)%20and%20B12,acid%20homeostasis%2C% gluconeogenesis, and amino acid metabolism, 20antioxidant%20generation%2C%20and including the conversion of pyruvate to oxaloacetate. MetabolicPathwayhttps://study.com/academy/lesson/what-i s-a-metabolic-pathway-definition-example.html#:~:text=The 7. B9 (folate) %20main%20metabolic%20pathways%20are,chain%2C% 20and%20the%20Cori%20cycle. Substrate for nucleotide synthesis and methyl-donors in the one-carbon metabolism pathway. Pathway: Folate plays a key role in the one-carbon metabolism, which is crucial for DNA synthesis and the production of red blood cells. It also helps in the methylation of homocysteine to form methionine. 8. B12 (cobalamin) Cofactor for enzymes in one-carbon metabolism and the propionate catabolic pathway. Pathway: It is involved in folate metabolism, DNA synthesis, and the conversion of odd-chain fatty acids into succinyl-CoA, a key intermediate in the citric acid cycle. GROUP 5 | BSMLS 2A 11