Transcript CH_18_2_Digestion_Foods

Chapter 18 Metabolic Pathways and
Energy Production
1
18.2
Digestion of Foods
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Stage 1: Digestion of Carbohydrates
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In stage 1,
• carbohydrates begin digestion in the mouth
• α-glycosidic bonds in amylose and amylopectin are hydrolyzed
by enzymes released from salivary glands
• smaller polysaccharides such as dextrins, maltose, and glucose
are produced
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Stage 1: Digestion of Carbohydrates
3
In stage 1,
• digestion continues in the small intestine, where enzymes
hydrolyze dextrins to maltose and glucose
• maltose, lactose, and sucrose are hydrolyzed to
monosaccharides, mostly glucose, which enter the bloodstream
for transport to the cells
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Carbohydrate Digestion
4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Digestion of Fats
5
In stage 1, the digestion of fats (triacylglycerols)
• begins in the small intestine, where bile salts break fat
globules into smaller particles called micelles
• requires enzymes from pancreas to hydrolyze
triacylglycerols to yield monoacylglycerols and fatty acids
absorbed by intestinal lining
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Digestion of Triacylglycerols
6
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Digestion of Proteins
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In stage 1, the digestion of proteins
• begins in the stomach, where HCl in stomach acid denatures
proteins and activates enzymes to hydrolyze peptide bonds
• continues in the small intestine, where smaller proteins are
completely hydrolyzed to amino acids
• ends as amino acids enter the bloodstream for transport
to cells
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Digestion of Proteins
8
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
9
Match the end products of digestion, amino acids, fatty acids and
glycerol, or glucose, with the types of food.
A. fats
B. proteins
C. carbohydrates
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
10
Match the end products of digestion, amino acids, fatty acids and
glycerol, or glucose, with the types of food.
A. fats
B. proteins
C. carbohydrates
fatty acids and glycerol
amino acids
glucose
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.