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 & moleculesare continuously moving& colliding

Activation energy is thecollision 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 energyenzymes speed up metabolic reactions to 10 billion times faster

essentially acts as a reaction organizer

Enzymes

Enzymes are protein molecules that act as catalystsEnzyme = apoenzyme + cofactor

Apoenzymes are the protein portionCofactors 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

Specificityacts 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

Regulationenzyme synthesisturning on or off by adding factors or functional groups that change enzyme shape

Temp, pH, electrolytesaffects 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

monomer polymer

carbohydrates monosaccharide polysaccharide

proteins amino acid polypeptides

lipidsfatty acids,

glyceroltriglycerides, phospholipids

nucleic acids nucleotides polynucleotides

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