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Overview of Biochemical Metabolism and Deficiency Diseases

Explore metabolic pathways, their regulation, clinical significance, and deficiency diseases including vitamin, mineral, and genetic enzyme disorders in this detailed biochemistry presentation.

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B I O C H E M I S T R Y Overview of Biochemical Metabolism Introduction & Classification • Understanding Metabolic Pathways • Deficiency Diseases Amit Kumar Singh Assistant Professor Department of Medical Laboratory Science Chandigarh University
Introduction to Metabolism Part A Metabolism (Greek: metabole = change) is the entire set of enzyme-catalyzed chemical reactions occurring continuously within a living cell/organism, which together sustain life. It converts nutrients into energy and building blocks, and eliminates waste. Organized: Reactions occur in defined, ordered sequences called pathways Regulated: Precisely controlled according to the body's changing needs Integrated: Pathways across tissues and organs communicate and coordinate Enzyme-driven: Almost every reaction is catalyzed by a specific enzyme M The Metabolic Funnel Stage I Macromolecules → building blocks Stage II Building blocks → Acetyl-CoA Stage III Acetyl-CoA oxidized (TCA + ETC) → CO2 + H2O + ATP 2
1. Conversion of complex molecules into their building blocks : Polysaccharides are broken down to monosaccharides lipids to free fatty acids and glycerol, proteins to amino acids. 2. Formation of simple intermediates : The building blocks produced in stage (1) are degraded to simple intermediates such as pyruvate and acetyl CoA. These intermediates are not readily identifiable as carbohydrates, lipids or proteins. A small quantity of energy (as ATP) is captured in stage 2. 3. Final oxidation of acetyl CoA : Acetyl CoA is completely oxidized to CO2, liberating NADH and FADH2 that finally get oxidized to release large quantity of energy (as ATP). Krebs cycle (or citric acid cycle) is the common metabolic pathway involved in the final oxidation of all energy-rich molecules. This pathway accepts the carbon compounds (pyruvate, succinate etc.) derived from carbohydrates lipids or proteins.
Importance of Biochemical Metabolism E Energy Production Converts food into usable ATP for contraction, conduction, transport & biosynthesis S Synthesis Builds proteins, nucleic acids, lipids, hormones & neurotransmitters G Growth & Repair Supplies building blocks for cell division and tissue healing D Detoxification Converts harmful substances (ammonia, drugs) into excretable forms H Homeostasis Maintains blood glucose, pH, electrolyte & osmotic balance R Reserve Storage Glycogen (short-term) and fat (long-term) energy reserves C Clinical Diagnosis Basis of blood glucose, lipid profile & liver function tests P Pharmacology Basis Most drugs act by modifying a metabolic step or enzyme 3
Classification — By Direction of Reactions Type Description Nature Examples Catabolism Breakdown of complex molecules into simple ones Exergonic, oxidative, convergent Glycolysis, β-oxidation, glycogenolysis Anabolism Synthesis of complex molecules from simple ones Endergonic, reductive, divergent Gluconeogenesis, glycogenesis, lipogenesis Amphibolic Pathways serving both catabolic & anabolic roles Dual function TCA cycle, HMP shunt Amphibolic pathways note TCA cycle is the classic amphibolic pathway: it oxidizes acetyl-CoA to release energy (catabolic role) AND supplies intermediates (e.g., oxaloacetate, α-ketoglutarate) for biosynthesis of amino acids, glucose, and heme (anabolic role). This dual role links it to nearly every other a pathway in the cell. 4
Classification — By Biomolecule, Site & Oxygen Requirement By Type of Biomolecule Carbohydrate metabolism — Glycolysis, gluconeogenesis, glycogenesis/-lysis, HMP shunt, TCA cycle Lipid metabolism — β-oxidation, lipogenesis, ketogenesis, cholesterol & lipoprotein metabolism Protein/amino acid metabolism — Transamination, deamination, urea cycle, protein synthesis Nucleic acid metabolism — Purine & pyrimidine synthesis and degradation Mineral & vitamin metabolism — Absorption, activation (e.g. Vit D) & utilization of micronutrients By Site / Location Intracellular: glycolysis (cytoplasm), TCA & β-oxidation (mitochondria), fatty acid synthesis (cytoplasm), urea cycle (mitochondria + cytoplasm) Organ-based: liver (central hub), muscle, adipose tissue, brain, kidney — each specialized By Oxygen Requirement Aerobic Requires O2 — oxidative phosphorylation, TCA cycle Anaerobic No O2 needed — glycolysis to lactate 5
Understanding Metabolic Pathways Part B Definition: A series of connected, sequential enzyme-catalyzed reactions in a cell, where the product of one reaction becomes the substrate of the next — converting a starting molecule into an end product. Types of Metabolic Pathways (by Structure) Linear A → B → C → D straight sequence EXAMPLE Glycolysis Cyclic End product regenerates the start molecule EXAMPLE TCA cycle, Urea cycle Spiral Same enzymes reused, substrate shortens each turn EXAMPLE β-oxidation of fatty acids Branched One pathway diverges or two converge EXAMPLE Amino acid metabolism 6
Key Features & Regulation of Metabolic Pathways 1 Irreversibility Key steps are essentially irreversible, catalyzed by rate- limiting regulatory enzymes 2 Compartmentalization Pathways localize to specific organelles, preventing conflicting reactions 3 Common intermediates Acetyl-CoA, Pyruvate & Glucose-6-P link pathways for integration 4 Energy coupling Endergonic steps are coupled with exergonic ATP hydrolysis Modes of Regulation Allosteric regulation — activators/inhibitors bind enzyme at a site other than active site Covalent modification — phosphorylation / dephosphorylation Hormonal control — insulin, glucagon, epinephrine, cortisol Enzyme induction/repression — gene-level control of enzyme amount Substrate/product concentration — mass action effects 7
Major Metabolic Pathways Pathway Purpose Location Glycolysis Glucose → Pyruvate (energy) Cytoplasm Gluconeogenesis Glucose synthesis from non-carb sources Liver, cytoplasm Glycogenesis Glucose → Glycogen (storage) Liver, muscle Glycogenolysis Glycogen → Glucose Liver, muscle TCA (Krebs) cycle Oxidation of Acetyl-CoA for energy Mitochondrial matrix β-oxidation Fatty acid breakdown for energy Mitochondria Lipogenesis Fatty acid synthesis Cytoplasm Urea cycle Ammonia detoxification Liver (mito. + cytoplasm) HMP shunt NADPH & ribose-5-phosphate production Cytoplasm 8
Why Understanding Pathways Matters Clinically 1 Blocked Pathways Enzyme deficiencies at any step block the pathway, causing toxic substrate accumulation and product deficiency — basis of inborn errors of metabolism 2 Drug Targets Drugs are often designed to inhibit a specific enzyme in a pathway — e.g., statins inhibit HMG-CoA reductase in cholesterol synthesis 3 Lab Diagnostics Pathway knowledge underlies interpretation of biochemical lab investigations used in everyday clinical practice Key takeaway: A metabolic pathway is only as strong as its rate-limiting enzyme — when that step fails (genetically or pharmacologically), the whole pathway's output changes predictably. 9
Overview of Deficiency Diseases Part C Definition: Deficiency diseases result from inadequate intake, absorption, or utilization of essential nutrients, disrupting specific metabolic pathways and producing characteristic clinical features. Protein-Energy Malnutrition (PEM) Kwashiorkor Cause: Severe protein deficiency (adequate calories) Edema Fatty liver Growth retardation Skin/hair changes Potbelly Marasmus Cause: Severe deficiency of both protein and calories Severe wasting Growth failure No edema 10
Vitamin Deficiency Diseases Vitamin Deficiency Disease Key Features Vitamin A Night blindness, Xerophthalmia Poor vision in dim light, corneal damage B1 (Thiamine) Beriberi Peripheral neuropathy, cardiac failure B2 (Riboflavin) Ariboflavinosis Cheilosis, glossitis, angular stomatitis B3 (Niacin) Pellagra Dermatitis, diarrhea, dementia (3 D's) B9 (Folate) Megaloblastic anemia Neural tube defects in fetus B12 (Cobalamin) Pernicious anemia Neurological deficits, glossitis Vitamin C Scurvy Bleeding gums, poor wound healing Vitamin D Rickets / Osteomalacia Bone deformities, weak bones Vitamin K Bleeding disorders Impaired blood clotting 11
Mineral Deficiency Diseases I Iron DISEASE Iron-deficiency anemia FEATURES Fatigue, pallor, microcytic hypochromic RBCs I Iodine DISEASE Goiter, Cretinism FEATURES Thyroid enlargement, impaired development C Calcium DISEASE Osteoporosis, tetany FEATURES Weak bones, muscle cramps Z Zinc DISEASE Growth retardation FEATURES Poor wound healing, skin lesions, immune dysfunction 12
Inborn Errors of Metabolism Genetically deficient/absent enzymes → substrate accumulation & product deficiency Disease Enzyme Deficient Pathway Features Phenylketonuria (PKU) Phenylalanine hydroxylase Amino acid metabolism Mental retardation, musty urine odor Albinism Tyrosinase Melanin synthesis Lack of skin/hair pigmentation Galactosemia Gal-1-P uridyltransferase Carbohydrate metabolism Liver damage, cataracts, retardation Von Gierke's disease Glucose-6-phosphatase Glycogen metabolism Hepatomegaly, severe hypoglycemia Gaucher's disease Glucocerebrosidase Lipid metabolism Hepatosplenomegaly, bone pain Maple syrup urine disease Branched-chain α-ketoacid DH Amino acid metabolism Sweet urine, neurological damage 13
Question- One molecule of glucose undergoes complete glycolysis under aerobic conditions. Calculate the total ATP and NADH molecules produced during glycolysis.
Quick Revision Summary Metabolism Organized, regulated, integrated reactions — catabolism + anabolism + amphibolic pathways Importance Energy, biosynthesis, detoxification, homeostasis, storage, diagnosis, pharmacology Classification By direction, by biomolecule, by site, by oxygen requirement Pathways Linear, cyclic, spiral, branched — regulated by allosteric control, hormones & enzyme induction Deficiency diseases Nutrient-based (vitamins/minerals/PEM) vs. genetic enzyme- based (inborn errors) 14