Introduction to Introduction to METABOLISMMETABOLISM

MetabolismMetabolismis the sum of all chemical changes occurring in a cell , tissue or the bodyIt is composed of pathwayspathways

PathwayPathwayis a multistep sequence of reactions is a multistep sequence of reactions in which the product of one reaction serves as the substrate of the subsequent in which the product of one reaction serves as the substrate of the subsequent reactionreactionEach reaction is catalyzed by a specific enzyme (may be with help of a coenzyme)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 intersectintersect forming a network of chemical reactions. K T A B C D E Pathways can be classified as either : L U cataboliccatabolic (degredative) or anabolicanabolic (synthetic) M V

Glycolysis, an example of a metabolic pathway

Metabolic mapMetabolic mapis a map that shows components of a pathways of metabolism It is useful in tracing connections between pathways

Example of aExample of a metabolic mapmetabolic map

metabolic map ofmetabolic map of intermediary

metabolism

Catabolic ReactionsCatabolic Reactions

• Catabolic reactions break down complex molecules such as proteins, polysaccharides and lipids to few simple molecules• Serve to: yield energy in the form yield energy in the form of ATP 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 building blocks needed for the synthesis of complex molecules

Catabolic & Anabolic ReactionsCatabolic & Anabolic Reactions

Anabolic ReactionsAnabolic Reactions

•Anabolic pathways form complex end products from simple precursors i.e. synthesis of glycogen from glucose & proteins from amino acids

• Requires energy Requires energy provided by breakdown of ATP to ADP & Pi

ANABOLIC CATABOLIC

Biosynthetic Degradative

Reductive Oxidative

Energy Required Energy Liberated

Diverging Converging

Decomposition of large complex molecules into small molecules

large complex organic molecules are constructed from small molecules

Catabolism

Many Few

Anabolism Few Many(converging)

(diverging)

Nutrients Carbohydrates Fats Proteins

End products H2O, CO2, NH3

Catabolism(oxidative, exergonicexergonic)

Macromolecules Proteins Polysaccharides Lipids Nucleic acids

Precursor Molecules Amino acids Sugars Fatty acids Nitrogenous bases

Anabolism (reductive,

endergonicendergonic)

Chemical energy

ATPNADPH

NADPH

NADPH

GTP

ATP

ATP

NADH

Catabolism and anabolism are always related.

Amphibolic PathwayAmphibolic Pathway

Amphi = Dual, amphibolic: dual pathwayAmphi = Dual, amphibolic: dual pathway

For example,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

Stages of CatabolismStages of Catabolism

• Citric acid cycle Citric acid cycle produces NADH & FADH2

• Electrons flow from NADH & FADH2 in the mitochondria (electron transport electron transport chainchain) generates energy in the form of ATP (oxidative phosphorylationoxidative phosphorylation).

Adenosine triphosphate Adenosine triphosphate ATPATP

(carrier of energy)

ATP ADP + Pi

ADP AMP + PiPi Pi Pi

MitochondriaMitochondria

BATTERY OF THE CELLBATTERY OF THE CELL

site for generating ATPsite for generating ATP

Through Through

Electron Transport Chain Electron Transport Chain

& &

Oxidative PhosphorylationOxidative Phosphorylation

In Electron Transport Chain 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 (phosphorylationphosphorylation)

Flow of electrons

NADH

Oxidative Phosphorylation (in mitochondria)Oxidative Phosphorylation (in mitochondria)

OxidationOxidation: electron flow in electron transport chain (with production of energy)

PhosphorylationPhosphorylation: phosphorylation of ADP to ATP

PHOSPHORYLATIOPHOSPHORYLATION

OXIDATION

NADH

ATPATP

Diet Carbohydrates Glycogen (liver & Sk. Ms.)Diet Carbohydrates Glycogen (liver & Sk. Ms.)

Glucose 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 ATPATP(oxidative phosphorylation)

CATABOLISM OF CATABOLISM OF CARBOHYDRATESCARBOHYDRATES

TriglyceridesTriglycerides

Fatty acids

Acetyl CoA

Citric acid cycle

ATPATPEnergy

Lipid CatabolismLipid Catabolism

amino group ((-ketoacid)-ketoacid) (nitrogen) (carbon skeleton)

incorporated into other excreted catabolised synthesisCompounds of other compounds (e.g. urea) acetyl CoA

Citric Acid Cycle ATP ATP (energy)

Protein Amino Acid

Protein CatabolismProtein Catabolism

DEAMINATION