DIGESTIVE SYSTEM & ENZYME NOTES

DIGESTIVE SYSTEM Includes mouth, pharynx, esophagus, stomach, small intestine and large intestine; several major glands and their secretions, including the salivary glands, the pancreas and the liver

Digestion is the breakdown of food into simpler molecules that can be absorbed and used by the cells of the body

THE PROCESS OF DIGESTION: 1. Mouth - teeth break up food in a process called mechanical digestion; also salivary glands secrete the first digestive enzymes (amylase and mucous) 2. Pharynx - the top part of the throat; no digestion takes place here

Esophagus - the muscles of the esophagus begin to contract in waves, pushing food toward the stomach; this is called peristalsis

4. Stomach - three secretions combine to form the gastric fluid:  Mucous - keeps food lubricated and protects walls of the stomach  Hydrochloric acid - helps break down food  Pepsin - mixes with hydrochloric acid to begin digesting proteins Food is churned for hours becoming a pasty mixture known as chyme

5. Small Intestine - the chyme is flooded with enzymes from three sources:

Duodenum (1 st part of small intestine) - releases enzymes that continue digesting Pancreas - releases pancreatic fluid that digests carbohydrates, proteins and fats Liver - secretes bile, which is stored in the gallbladder, which breaks down fats further

5. Small Intestine - the now mostly digested food passes through the rest of the small intestine where nutrients are absorbed into the bloodstream; when it LEAVES the SMALL INTESTINE, the food is NUTRIENT FREE

Absorption in the Small Intestine The small intestine increases SURFACE AREA to increase absorption The folded surfaces are fingerlike projections called villi

6. Large Intestine (Colon) - main job is to remove water from undigested materials passing through it 7. Rectum – store feces (solid waste)

Mouth Pancreas Salivary Glands Pharynx Esophagus Liver Stomach Tongue Large Intestine Small Intestine Appendix Rectum Anus Stomach Pancreas Gallbladder Liver

Enzymes Used in Digestion EnzymeSite of ActionSite of ProductionNutrient Digested Amylase Mouth Salivary Glands Carbohydrate Pepsin Stomach Lining of Stomach Protein LipaseSmall Intestine PancreasFat Amylase Small Intestine Pancreas Carbohydrate Trypsin Small Intestine Pancreas Protein LactaseSmall Intestine Lining of Small IntestineCarbohydrate Maltase Small IntestineLining of Small Intestine Carbohydrate Sucrase Small Intestine Lining of Small Intestine Carbohydrate Peptidase Small Intestine Lining of Small Intestine Protein

Chemical Reactions Chemical Reaction – process that changes one set of chemicals into another set of chemicals Reactants – elements or compounds that enter into a chemical reaction Products – elements or compounds produced by a chemical reaction Example: 2H 2 + O 2  2 H 2 O  Reactants Product

Chemical Reactions Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products Energy is released or absorbed whenever chemical bonds form or are broken

Enzymes Catalyst – substance that speeds up the rate of a chemical reaction Enzymes – proteins that act as biological catalysts (speed up chemical reactions that take place in cells) Enzymes help lower the activation energy of a chemical reaction (the energy needed to get a reaction started)

Enzymes The reactants of enzyme- catalyzed reactions are known as substrates Substrates bind to a site on the enzyme called the active site

______________ ___________ Substrate Products Enzyme Active Site

The fit between the active site and substrates is so precise that it is often compared to a lock and key This is the old model

New Model - Induced fit The induced-fit theory assumes that the substrate plays a role in determining the FINAL SHAPE of the enzyme and that the enzyme is partially FLEXIBLE. Only the proper substrate is capable of inducing the proper alignment of the active site.

Notice the difference in shape Before and during binding and after