Metabolism of the Body PDF 2024

# Metabolism of the Body **Assist. Prof. Dr. Galal M. Alsakaf** **2024** ## Energy and Metabolism 1. The energy that runs most biological systems on earth comes from solar energy. 2. Plants trap solar energy for reactions of Photosynthesis by producing their food. 3. The food we eat, (carbohydrat...

# Metabolism of the Body **Assist. Prof. Dr. Galal M. Alsakaf** **2024** ## Energy and Metabolism 1. The energy that runs most biological systems on earth comes from solar energy. 2. Plants trap solar energy for reactions of Photosynthesis by producing their food. 3. The food we eat, (carbohydrates, lipids, proteins, and Nucleic Acids), are our source of energy for doing the biological work of cells. 4. All molecules (nutrient molecules included) have stored (potential) energy in the bonds between their atoms. ## Metabolic Overview: The Absorptive State | Nutrient Source | Distributed in Bloodstream | Destinations| |---|---|---| | Nutrients absorbed at digestive tract | Lipids | ADIPOSE TISSUE: Use: storage as triglycerides, Stimulated by: Insulin | | | Amino acids | SKELETAL MUSCLE: Use: ATP production, Stimulated by: Insulin | | | Glucose | ALL TISSUES: Use: protein synthesis, Stimulated by: Insulin, GH, androgens/estrogens | | | | ALL TISSUES (except skeletal musele): Use: ATP production, Stimulated by: Insulin | | | | LIVER AND SKELETAL MUSCLE: Use: storage as glycogen, Stimulated by: insulin | ## Three Basic Uses of Absorbed Nutrients 1. Energy for immediate use by cells to conduct their normal processes (Muscle contraction, secretions, active transport). 2. Synthesize structural or functional molecules to repair and replace cells by (Mitosis and Cytokinesis) 3. Storage as glycogen or fat for later use as energy (nutrient reserves). ## Metabolism **Metabolism is the ability to acquire and use energy from the environment.** **Metabolic processes are all the chemical reactions that occur in cells, tissues, organs, and organ systems.** **All living things from bacteria to humans conduct metabolism.** **Two Kinds of Metabolic Reactions:** * Catabolism = breakdown of large molecules into simple ones to produce energy. (release energy) * Anabolism = build large molecules from simple molecules. (requires energy input) ## Cellular Respiration * When oxygen is used these processes are called Aerobic Cell Respiration. * The final products: $CO_2$, water and energy. * Part of this energy is used for ATP formation. * Fuel Nutrient + $O_2$ --> $CO_2$ +$H_2O$ + energy ## The ATP * Catabolic reactions in cells liberate energy packaged in the phosphate bonds of ADP (Adenosine Diphosphate) to produce the high energy molecules of ATP (Adenosine TriPhosphate * ADP + Pi+ energy -----→ ATP * ATP is the universal energy carrier of the cell. * ATP --------→ ADP + Pi + energy ## The Hydrogen Carriers * They are coenzymes: function as energy and H carriers * Carry the hydrogen to the cristea. * (NAD) Nicotinamide Adenine Dinucleotide derived from Niacin (vit.B3). * (FAD) Flavin Adenine Dinucleotide, derived from riboflavin (vit.B2). * Each FAD can accept 2H * FAD-----→ FADH2 (reduced). * Each NAD can accept 2e but can bind one proton * NAD ---->NADH+H+(reduced) ## Carbohydrate (Gluose) Metabolism in Four Steps ### 1. Glycolysis * It is the metabolic pathway by which Glucose ($C_6$) is converted into two molecules of pyruvic acid. * It is a metabolic pathway involve many enzymatically controlled steps. * It takes place in the cytoplasm of the cell. A diagram of glycolysis shows the steps in the conversion of Glucose into Pyruvate. ## Stage 2: Aerobic Respiration ### 2. Pyruvate Oxidation (transition reaction). * Transfers pyruvate to the mitochondria. * 2Pyruvic acid from glycolysis diffuses into matrix of the mitochondria & carried by 2 coenzyme A to form 2 acetyl-CoA and 2CO2 and 2NADH are also produced. A diagram of the pyruvate oxidation reaction shows the conversion of pyruvate into acetyl-CoA. ## Stage 3: Kreb's Cycle * Acetyl-CoA is introduced into a cycle of 9 reactions called the Krebs cycle. * It is also called the citric acid cycle, for the citric acid, or citrate, formed in its first step. * To metabolize glucose, requires 2 cycles. * Metabolic pathway that indirectly requires $O_2$. * Acetyl Co.A (2C) enters the Kreb's Cycle & joins with Oxaloacetic Acid (4C) to make Citric Acid (6C). * Citric acid is oxidized releasing $CO_2$, free $H^+$, & e- and forming ketoglutaric acid (5C). A diagram of the Krebs cycle shows the steps involved in the process. ## Stage 4: Electron Transport System * The respiratory chain involves four large protein complexes (I-IV) as well as ATP synthase (AS). * All of these are embedded in the inner mitochondrial membrane. 1. Flavoprotein (derived from vit. Riboflavin). 2. Coenzyme Q (derived from vit. E). 3. A group of Cytochromes. The last of these is cytochrome a3. A diagram of the electron transport system shows how electrons, NADH, and FADH2 are used to create ATP ## Summary of ATP Production A diagram summarises the production of ATP during glycolysis, pyruvate oxidation and the Krebs cycle. ## Lipid Metabolism * The pathway for catabolism of fatty acids is referred to as the ß-oxidation pathway, because oxidation occurs at the ß-carbon (C-3). * Triglycerides are the most abundant dietary lipids. * Each Triglyceride has a glycerol backbone to which are bind 3 fatty acids. * Lipase enzymes hydrolyze Triglycerides, into glycerol and three fatty acids (Lipolysis) ## ß-oxidation * Fatty acid ß-oxidation is considered to occur in the mitochondrial matrix. * Fatty acids must enter the matrix to be oxidized. * The ß-oxidation pathway is cyclic. * The product; 2 carbons shorter, is the input to another round of the pathway. * ATP molecule is needed to activate the F.A. * In every ß- oxidation the products : * One FADH2 * One NADH * Acetyl CoA and * Fatty acid with 2 carbon shorter. * This process continues until the entire, fatty acid is converted to acetyl CoA. * Acetyl Co.A enters Kreb's cycle, to make more ATP, $CO_2$, $H_2O$.