major food groups
Post on 02-Jan-2016
13 Views
Preview:
DESCRIPTION
TRANSCRIPT
Major food groups• Carbohydrates = sugars = saccharides• Lipids = fats• Proteins• nucleic acids
Carbohydrates, proteins and nucleic acids (but not fats) are long chains of smaller subunits, which are monomers. The combinations are polymers.
Polymers in which the order of monomers provides information: proteins and nucleic acids.
Copyright © 2009 Pearson Education, Inc.
Nucleic acid digestion- pancreatic ribonuclease & deoxyribonuclease; nucleosidases & phosphatases; act in small intestines
Copyright © 2009 Pearson Education, Inc.
Composition and Function of Pancreatic Juice
• Many enzymes are secreted in inactive form:
Examples include:– Trypsinogen is activated to trypsin– Pepsinogen activated to pepsin by HCl– Procarboxypeptidase is activated to
carboxypeptidase
Copyright © 2009 Pearson Education, Inc.
• Digestive enzymes that are produced by the small intestine are all brush border enzymes (membrane-bound)
• Advantages and disadvantages of having membrane-bound enzymes
Copyright © 2010 Pearson Education, Inc.
Figure 23.27 Activation of pancreatic proteases in the small intestine.
Stomach
Pancreas
Epithelialcells
Trypsinogen(inactive)Chymotrypsinogen(inactive)Procarboxypeptidase(inactive)
Trypsin
Chymotrypsin
Carboxypeptidase
Membrane-boundenteropeptidase
Copyright © 2010 Pearson Education, Inc.
Protein digestion
+
• Amino acids enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.
Smallintestine
Smallintestine
Stomach
Foodstuff
Protein
Large polypeptides
Pepsin(stomach glands)in presence of HCl
Small polypeptides,small peptides
Pancreaticenzymes (trypsin, chymotrypsin,carboxypeptidase)
Amino acids
Brush border enzymes (small intestine)
Path of absorptionEnzymes
and sourceSite ofaction
Copyright © 2010 Pearson Education, Inc.
Figure 23.33 Protein digestion and absorption in the small intestine.
Absorptiveepithelialcell
Apical membrane (microvilli)
Aminoacid carrier
Capillary
Lumen of intestine
Pancreaticproteases
Amino acids of protein fragmentsBrush border enzymes
1Protein fragments (peptides) are digested to amino acids by brush border enzymes of mucosal cells.
2 The amino acids are then absorbed by active transport into the absorptive cells
3 The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts.
Active transport
Passive transport
Copyright © 2010 Pearson Education, Inc.
Carbohydrate digestion
• All monosaccharides enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.
Starch and disaccharides
Oligosaccharidesand disaccharides
Lactose Maltose Sucrose
Glucose Fructose
Salivaryamylase
Mouth
Pancreaticamylase
Brush borderenzymes in small intestine
Smallintestine
Smallintestine
Foodstuff
Galactose
Path of absorptionEnzyme(s)and source
Site ofaction
Copyright © 2010 Pearson Education, Inc.
Fat digestion
Small intestine
Small intestine
Foodstuff
Unemulsifiedfats
Emulsification by the detergent action of bile salts from theliver
Pancreatic lipases
fatty acids glycerol
Path of absorptionEnzyme(s)and source
Site ofaction
• Fatty acids and glycerol enter the intestinal cells via diffusion.
• Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells to make chylomicrons, which are extruded by exocytosis.
• The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct.
Note: fats are NOT made of a long chain of monomers (unlike proteins and polysaccharides)
Copyright © 2010 Pearson Education, Inc.
Figure 23.34 Emulsification, digestion, and absorption of fats.
Epithelialcells ofsmallintestine
Fat dropletscoated withbile salts
Fat globule
Lacteal
Bile salts
Fatty acidsand bile salts
1 Large fat globules are emulsified (physically broken up into smaller fat droplets) by bile salts in the duodenum.
2 Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and glycerol, still associated with bile salts
3 Fatty acids and glycerol diffuse into epithelial cells. There they are recombined and packaged with other lipids and proteins to form chylomicrons.
4 Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals. They are carried away from the intestine by lymph.
Copyright © 2010 Pearson Education, Inc.
Nucleic acid digestion
• Subunits are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein.
Smallintestine
Smallintestine
Foodstuff
Nucleic acids
Pancreatic ribo-nuclease and deoxyribonuclease
Brush borderenzymes(nucleosidasesand phosphatases)
Pentose sugars,N-containing bases,
phosphate ions
Path of absorptionEnzyme(s)and source
Site ofaction
Copyright © 2009 Pearson Education, Inc.
In the large intestine:
• Other than digestion by enteric bacteria, no further digestion takes place– Bacteria synthesize B complex vitamins and vitamin K
• water, and electrolytes are absorbed
top related