Ex 39A Digestive Enzymes

Energy Transfer in Chemical Reactions Forming new bonds can either release or absorb energy Chemical reactions usually involve both exergonic reactions release more energy than they absorb endergonic reactions absorb more energy than they release Human metabolism couples exergonic and endergonic reactions, so that the energy released from one reaction will drive the other. Glucose breakdown releases energy used to build ATP molecules that store that energy for later use in other reactions

Activation Energy Atoms, ions & molecules are continuously moving & colliding Activation energy is the collision energy needed to break bonds & begin a reaction Increases in concentration & temperature, increase the probability of 2 particles colliding more particles in a given space as concentration is raised particles move more rapidly when temperature is raised

Catalysts or Enzymes Normal body temperatures and concentrations are too low to cause chemical reactions to occur Catalysts speed up chemical reactions by lowering the activation energy needed to get it started Catalysts orient the colliding particles properly so that they touch at the spots that make the reaction happen Catalyst molecules are unchanged and can be used repeatedly to speed up similar reactions.

Effectiveness of Catalysts Catalysts speed up chemical reactions by: lowering the activation energy not consumed in the reaction do not affect the direction of a reaction

Enzyme Functions Enzymes speed up reactions by properly orienting substrates and thereby lowering the activation energy enzymes speed up metabolic reactions to 10 billion times faster essentially acts as a reaction organizer

Enzymes Enzymes are protein molecules that act as catalysts Enzyme = apoenzyme + cofactor Apoenzymes are the protein portion Cofactors are nonprotein “helpers” may be metal ion (iron, zinc, magnesium or calcium) may be organic molecule derived from a vitamin Enzymes usually end in suffix -ase and are named for the types of chemical reactions they catalyze

Enzyme Functionality Specificity acts on only one substrate active site speed up only one reaction but don’t make new reactions occur (without the enzyme the reaction would still occur)

Enzyme Functionality Regulation enzyme synthesis turning on or off by adding factors or functional groups that change enzyme shape Temp, pH, electrolytes affects function by changing enzyme structure lysozymes

Enzyme Functionality Saturation Limit

Enzyme Functionality Enzyme Inhibitors competitive blocks the active site of the enzyme so other substrates cannot bind noncompetitive inactivates the enzyme by binding to it and changing its shape

Chemical Reactions Condensation Reactions (dehydration synthesis) two molecules combine water is created as a byproduct

Chemical Reactions Hydrolysis one molecule broken apart into two smaller ones water add to the reaction to create the final products most digestive enzymes work through creating hydrolysis reactions

Macromolecules monomerpolymer carbohydratesmonosaccharidepolysaccharide proteinsamino acidpolypeptides lipidsfatty acids, glycerol triglycerides, phospholipids nucleic acidsnucleotidespolynucleotides

Digestion and Absorption Digestion breaking down large molecules into smaller ones starch into sugar monomers proteins into amino acids triglycerides into fatty acids and glycerol occurs via secreted enzymes and brush border enzymes Absorption once large molecules digested down to their monomers they can pass into the cell, then into the blood

Digestion: Carbohydrates Secreted enzymes breaks down starch to oligosaccharides, trisaccharides, disaccharides salivary amylase (minor) inactivated by stomach acid pancreatic amylase (major) amylase in breast milk

Digestion: Carbohydrates brush border enzymes on microvilli of small intestine breaks down into monosaccharides lactase lactose to glucose + galactose maltase maltose to glucose + glucose sucrase sucrose to glucose + fructose

Digestion: Carbohydrates Detecting carbohydrate digestion in lab Lugol’s IKI turns black in presence of starch Benedict’s Solution turns orange in presence of glucose or maltose

Digestion: Protein Secreted enzymes breaks protein down into smaller polypeptides HCL in stomach denatures protein so secreted enzymes can work pepsin secreted by gastric chief cells pancreatic enzymes trypsin, elastase, carboxypeptidase, chymotrypsin breaks down into peptides

Digestion: Protein 1. brush border membrane peptidase small peptides/ amino acids 2. membrane amino acid transporter 3. membrane di/tripeptide transporter 4. intracellular peptidases amino acids 5. basolateral membrane amino acid carrier 6. basolateral membrane di/tripeptide carrier

Digestion: Protein Detecting protein digestion in lab BAPNA amino acid bound to a dye enzyme cleaves the amino acid from the dye causing color change to yellow

Digestion: Lipids Emulsification bile salts from the liver cause large fat drops to form small fat droplets allows water soluble lipase to work on digesting the fat Secreted enzymes breaks triglycerides into monoglycerides and fatty acids gastric lipase (20%) chief cells in fundus pancreatic lipase (80%) milk derived lipase (glycerol and fatty acids)

Digestion: Lipids Detecting lipid digestion in lab Litmus cream purple pH indicator in cream turns pink in presence of fatty acids