Introduction to METABOLISM

Metabolism is the sum of all chemical changes occurring in a cell , tissue or the body It is composed of pathways Pathway is a multistep sequence of reactions in which the product of one reaction serves as the substrate of the subsequent reaction Each reaction is catalyzed by a specific enzyme (may be with help of a coenzyme) A B C D E F G 1 2 3 4 5 6 Different pathways can intersect forming a network of chemical reactions. K T A B C D E Pathways can be classified as either : L U catabolic (degredative) or anabolic (synthetic) M V

Glycolysis, an example of a metabolic pathway

Metabolic map is a map that shows components of a pathways of metabolism It is useful in tracing connections between pathways metabolic map of intermediary metabolism Example of a metabolic map

Catabolic & Anabolic Reactions Catabolic Reactions Catabolic reactions break down complex molecules such as proteins, polysaccharides and lipids to few simple molecules Serve to: yield energy in the form of ATP from the degradation of energy- rich fuel molecules Allow molecules in the diet (or nutrient molecules stored in the cells) to be converted into building blocks needed for the synthesis of complex molecules Anabolic Reactions Anabolic pathways form complex end products from simple precursors i.e. synthesis of glycogen from glucose & proteins from amino acids Requires energy provided by breakdown of ATP to ADP & Pi

ANABOLIC CATABOLIC Biosynthetic Degradative Reductive Oxidative large complex organic molecules are constructed from small molecules Decomposition of large complex molecules into small molecules Biosynthetic Degradative Reductive Oxidative Energy Required Energy Liberated Diverging Converging

Catabolism Anabolism (diverging) (converging) Few Many Many Few

Catabolism(oxidative, exergonic) Anabolism (reductive, endergonic) Macromolecules Proteins Polysaccharides Lipids Nucleic acids Nutrients Carbohydrates Fats Proteins GTP ATP NADPH Catabolism(oxidative, exergonic) Anabolism (reductive, endergonic) NADPH Chemical energy NADPH NADH ATP ATP Precursor Molecules Amino acids Sugars Fatty acids Nitrogenous bases End products H2O, CO2, NH3 Catabolism and anabolism are always related.

Amphi = Dual, amphibolic: dual pathway Amphibolic Pathway Amphi = Dual, amphibolic: dual pathway For example, Krebs cycle is mainly a catabolic cycle, but with some anabolic features. e.g. part of Krebs cycle is used for the synthesis of glucose from amino acids Therefore, Krebs cycle is amphibolic 9

Stages of Catabolism Citric acid cycle produces NADH & FADH2 Electrons flow from NADH & FADH2 in the mitochondria (electron transport chain) generates energy in the form of ATP (oxidative phosphorylation).

Adenosine triphosphate ATP (carrier of energy) ATP ADP + Pi ADP AMP + Pi Pi Pi Pi

Mitochondria BATTERY OF THE CELL site for generating ATP Through Electron Transport Chain & Oxidative Phosphorylation

In Electron Transport Chain in the mitochondria Flow of electrons from NADH & FADH2 (through electron carriers CoQ & cytochromes) to oxygen yields energy This energy is used for phosphorylation of ADP to ATP (phosphorylation)

Flow of electrons NADH

ATP PHOSPHORYLATION OXIDATION NADH Oxidative Phosphorylation (in mitochondria) Oxidation: electron flow in electron transport chain (with production of energy) Phosphorylation: phosphorylation of ADP to ATP

Diet Carbohydrates Glycogen (liver & Sk. Ms.) Glucose GLYCOLYSIS (in cytoplasm) Lactate Pyruvate in mitochondria Acetyl CoA Citric Acid Cycle (in mitochondria) NADH & FADH2 Electron transport chain (flow of electrons) Formation of ATP (oxidative phosphorylation) CATABOLISM OF CARBOHYDRATES

Triglycerides Fatty acids Acetyl CoA Citric acid cycle ATP Energy Lipid Catabolism

Protein Catabolism Protein Amino Acid amino group (a-ketoacid) (nitrogen) (carbon skeleton) incorporated into other excreted catabolised synthesis Compounds of other compounds (e.g. urea) acetyl CoA Citric Acid Cycle ATP (energy) DEAMINATION