The Four Stages of Food Processing
• Ingestion is another word for eating.
• Digestion is the breakdown of food into molecules
small enough for the body to absorb.
• Absorption is the uptake of the small nutrient
molecules by cells lining the digestive tract.
• Elimination is the disposal of undigested materials
left over from food.
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14Digestion: A Closer Look
• The dismantling of food molecules is necessary
because food molecules are
– too large to cross the membranes of animal cells and
– different from molecules that make up an animal’s body.
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15
• Mechanical digestion
– begins the process and
– involves physical processes like chewing.
• Chemical digestion is the chemical breakdown of
food by digestive enzymes.
Digestion: A Closer Look
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16 Figure 22.2
Cheese protein(a polymer ofamino acids ina specific sequence)
Amino acidmonomer
Amino acids
Human protein
Breakdown of proteinby human digestivesystem
Absorption of amino acids by cells lining thesmall intestine; transport via bloodstream toother cells
Cells use amino acidsfrom the cheese andother foods to producenew human proteins
1
2
3
17
Figure 22.2a
Cheese protein(a polymer of amino acids in a specific sequence)
Amino acidmonomer
Amino acids
Breakdown of proteinby human digestivesystem
1
18 Figure 22.2b
Human protein
Absorption of amino acids by cells lining the small intestine; transport via bloodstream to other cells
Cells use amino acids from the cheese and other foods to produce new human proteins
2
3
19
Figure 22.2c 20
• Chemical digestion proceeds via hydrolysis,
chemical reactions that break down polymers into
monomers using water in the process.
• Like most biological reactions, digestion also
requires enzymes.
Digestion: A Closer Look
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21
Figure 22.3
Enzyme (pepsin)
Enzyme (amylase)
Enzyme (lipase)
Protein
Carbohydrate
Fat
Amino acid
Fatty acidGlycerol
Sugar
H2O
H2O
H2O
H2O
H2O
HOH
HOH
22 Figure 22.3a-1
Enzyme (pepsin)
Protein
H2O
23
Figure 22.3a-2
Enzyme (pepsin)
Protein
H2OAmino acid
HOH
24 Figure 22.3b-1
Enzyme (amylase)
Carbohydrate
H2O
25
Figure 22.3b-2
Enzyme (amylase)
Carbohydrate
SugarH2O
HOH
26 Figure 22.3c-1
Enzyme (lipase)
Fat
H2O
H2O
H2O
27
Figure 22.3c-2
Enzyme (lipase)
FatFatty acid
GlycerolH2O
H2O
H2O
28