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Transcript 
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
Digestion of carbohydrates, proteins and
fats all occur by the process of
hydrolysis
breaking bond by insertion of H2O
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)
CH OH
2
H
O
H
OH
H
H
OH
a-amylase
HOH
CH OH
H
H
2
H
O
a 1,4 linkage
CH OH
2
H
O
H
OH
H
H
OH
O
CH OH
2
O
H
H
OH
H
H
OH
H
OH
HO
O
H
H
OH
H
H
OH
O
CELLULOSE
cellullase
HOH
CH OH
CH OH
2
2
O
H
H
H
O
H
O
OH
H
H
OH
H
b 1,4 linkage
O
OH
H
H
OH
H
GLYCOGEN
amylase
a 1,4 linkage
CH OH
2
H
CH OH
2
O
H
H
OH
H
H
OH
H
O
H
H
OH
H
H
OH
O
CH OH
2
H
O
a 1,6 linkage
CH
2
O
H
H
OH
H
H
OH
H
O
a 1,4 linkage
amylase
O
H
H
OH
H
H
OH
O
a-amylase
G
G
G
G
G
G
G
G
G
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
NH
Rn
O
C
C
NH
Rm
O
C
C
H
H
HOH
protease
NH
Rn
O
C
C
OH
HN
Rm
O
C
C
2
H
carboxy
terminus
amino H
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
HC
O
C
O
C
O
C
O
2
HC
O
HC
O
CH
3
CH
3
CH
2
3
HOH
lipase
HC
OH
2
HC
O
C
O
2-monoglyceride
CH
3
HC
OH
2
HO
O
C
2 fatty acids
CH
3
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