Digestion and Absorption Digestion breakdown of large particles

Digestion and Absorption

Digestion = breakdown of large particles and molecules into smaller molecules • Intracellular – Within food vacuoles; cells – Evolutionarily…more primitive – Lysosomes • Extracellular – Lumen of digestive tract – More advanced, active animals – Mechanisms for grinding up, breaking down food – Advantages:

Digestion and Body Plans Sac Body • primitive forms • single opening • mixing with wastes Tube Within a Tube • higher animals • separate opening for mouth & anus • gut specialization

Digestion of carbohydrates, proteins and fats all occur by the process of hydrolysis breaking bond by insertion of H 2 O

Hydrolytic reactions of digestion are catalyzed by enzymes: Carbohydrates and oligosaccharides: • carbohydrases • glycosidases Proteins and peptides: • proteases • peptidases Fats: • lipases ALL are hydrolytic enzymes.

CARBOHYDRATES STARCH (AMYLOSE) a-amylase HOH a 1, 4 linkage

CELLULOSE cellullase HOH b 1, 4 linkage

GLYCOGEN amylase a 1, 4 linkage a 1, 6 linkage a 1, 4 linkage amylase

a-amylase G G G G maltose isomaltose

Complex carbohydrates, polysaccharides and disaccharides broken down to monosaccharides (simple sugars) pancreatic g-amylase - exocarbohydrase pancreatic a-amylase - endocarbohydrase Small intestine maltase - G G 2 G isomaltase - 2 G G G

F sucrase (invertase) - F G G Ga lactase - Ga G G

PROTEINS peptide bond HOH protease carboxy terminus amino terminus

Activation of Pepsin in Stomach

Activation of Proteases in Small Intestine Enterokinase

Small Intestinal Proteases Enzyme Substrate enterokinase endo-, trypsinogen -> trypsin aminopeptidase exo-, amino terminal a. a. dipeptidase dipeptides -> 2 amino acids Proteins and polypeptides broken down to individual amino acids

FATS & LIPIDS Triglyceride HOH lipase 2 -monoglyceride 2 fatty acids