Cellular Metabolism Chapter 4 Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Introduction A living cell is the site of enzyme-catalyzed metabolic reactions that maintain life. Metabolic processes – all chemical reactions that occur in the body Many reactions form cycles or pathways

Metabolic Processes There are two (2) types of metabolic pathways: Anabolism Larger molecules are made from smaller ones Requires energy Catabolism Larger molecules are broken down into smaller ones Releases energy The reactions of metabolism are often reversible

Anabolism Anabolism provides the materials needed for cellular growth and repair Example: Dehydration synthesis Type of anabolic process Used to make polysaccharides, triglycerides, and proteins Produces water by joining two smaller molecules CH2OH H OH O Monosaccharide + HO Disaccharide H2O Water

Anabolism + + H O H O H C OH HO C (CH2)14 CH3 H C O C (CH2)14 CH3 O O Glycerol + 3 fatty acid molecules Fat molecule (triglyceride) + 3 water molecules Peptide bond H H H H H O O R R H O H O H H H O O N C C N C C N N C C C C N N C C C C OH OH H2O H O H H O H H H R R R R H H H H Amino acid + Amino acid Dipeptide molecule + Water

Catabolism Catabolism breaks down larger molecules into smaller ones Example: Hydrolysis A catabolic process Used to decompose carbohydrates, lipids, and proteins Water is used to split the substances Reverse of dehydration synthesis HO CH2OH H OH O Monosaccharide + Disaccharide H2O Water

Catabolism + + H O H O H C OH HO C (CH2)14 CH3 H C O C (CH2)14 CH3 O O Glycerol + 3 fatty acid molecules Fat molecule (triglyceride) + 3 water molecules Peptide bond H H H H H O O R R H O H O H H H O O N C C N C C N N C C C C N N C C C C OH OH H2O H O H H O H H H R R R R H H H H Amino acid + Amino acid Dipeptide molecule + Water

Control of Metabolic Reactions Enzymes Metabolic reactions include hundreds of chemical changes that must occur in particular sequences. Control rates of metabolic reactions Lower activation energy needed to start reactions Most are globular proteins with specific shapes Not consumed in chemical reactions Substrate specific Shape of active site determines substrate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Substrate molecules Product molecule Active site Enzyme molecule Enzyme-substrate complex Unaltered enzyme molecule (a) (b) (c)

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4.3: Control of Metabolic Reactions Enzyme Action 4.3: Control of Metabolic Reactions Enzymes (Catalysts) Control rates of metabolic reactions Lower activation energy needed to start reactions Most are globular (complex) proteins with specific shapes Not consumed in chemical reactions, recycled by the cell Substrate specific Shape of active site determines substrate Speed depends on the number of enzyme/substrate molecules available. Product molecule Active site (a) (b) (c) Substrate molecules Unaltered enzyme molecule Enzyme-substrate complex Enzyme

Enzyme Action Metabolic pathways Enzyme names commonly: Series of enzyme-controlled reactions leading to formation of a product Each new substrate is the product of the previous reaction Substrate 1 Enzyme A Substrate 2 Enzyme B Substrate 3 Enzyme C Substrate 4 Enzyme D Product Enzyme names commonly: Reflect the substrate Have the suffix – ase Examples: sucrase, lactase, protease, lipase

Regulation of Metabolic Pathways Limited number of regulatory enzymes Negative feedback Inhibition Rate-limiting Enzyme A Substrate 1 Substrate 2 Enzyme B Substrate 3 Enzyme C Substrate 4 Enzyme D Product

Cofactors and Coenzymes Make some enzymes active Non-protein component Ions or coenzymes Coenzymes Organic molecules that act as cofactors Vitamins Example: coenzyme A

Factors That Alter Enzymes Factors that alter (denature) enzymes: Heat Radiation Electricity Chemicals Changes in pH

Energy for Metabolic Reactions Energy is the capacity to change something; it is the ability to do work Common forms of energy: Heat Light Sound Electrical energy Mechanical energy Chemical energy Energy can be changed from one form to another. Through cellular respiration, energy is transferred from molecules to make it available for cellular use.

Release of Chemical Energy Chemical bonds are broken to release energy We burn glucose in a process called oxidation LEO says GER

ATP Molecules Adenosine triphosphate (ATP) carries energy in a form that the cell can use Each ATP molecule has three parts: An adenine molecule A ribose molecule Three phosphate molecules in a chain P P P Energy transferred and utilized by metabolic reactions when phosphate bond is broken Energy transferred from cellular respiration used to reattach phosphate P P P P