This document summarizes the digestion of proteins, carbohydrates, and fats. It discusses the enzymes involved in breaking down each macronutrient in the mouth, stomach, and small intestine. For carbohydrates, enzymes like amylase and disaccharides break starches and sugars into glucose. Proteins are broken into peptides and amino acids by pepsin and pancreatic proteases. Lipids are emulsified and hydrolyzed by lipases like pancreatic lipase into fatty acids and monoglycerides. The end products of digestion are absorbed for energy and building materials.

1. DIGESTION OF PROTEINS, FATS &
CARBOHYDRATES
DR INDRAJEET YADAV

2. Fatcarbohydrate protein
INTRODUCTION

3. INTRODUCTION
 ESSENTIAL:
� Sufficent water
 Adequate calories
� Protein
 fat
 Minerals
� vitamins
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� Cabohydrate
� Protein
Fat
1gm/kg
13:13

4. 13:13
HYDROLYSIS

5. HYDROLYSIS

6. 3
STARCH
LACTOSE
O
T
H
E
R
S
SUCROSE
AMYLOSE
GLYCOGEN
PYRUVIC ACID
DEXTRINS
ALCOHOL
LACTIC ACID
CARBOHYDRATE FOODS IN DIET
DIGESTION OF CARBOHYDRATES

7. AMYLOSE
AMYLOPECTIN
MALTOSE
𝜶 1-4 bond
𝜶 1-6 bond
DIGESTION OF CARBOHYDRATES

8. DIGESTION OF CARBOHYDRATES
AMYLASE
Maltose
Maltriose
Glucose oligomer
𝜶-limit dextrin

9. DIGESTION OF CARBOHYDRATES
+
+
GLUCOAMYLASE
ISOMALTASE
SUCRASE
MALTOSE
MALTRIOSE
𝜶-limit dextrin
GLUCOAMYLASE
ISOMALTASE
GLUCOAMYLASE
SUCRASE
ISOMALTASE
GLUCOSE
GLUCOSE

10. ENZYMES SPECIFICITY/SUBSTRATE
SUCRASE 𝜶 1-4 bond: maltose, maltotriose, sucrose
ISOMALTASE
𝜶 1-4 bond: maltose, maltotriose
𝜶 1-6 bond: 𝜶 limit dextrins
GLUCOAMYLASE 𝜶 1-4 bond: maltose, maltotriose
LACTASE lactose
13:13

11. DIGESTION OF CARBOHYDRATES
7
6
5
4
3
2
1
Continue in fundus and
body of stomach
𝜶-AMYLASE
SECRETED BY PAROTID
GLAND
Main form - maltose PTYALIN
30-40% of starch hydrolyzed
until food completely mixed with
gastric secretion
STARCH
Endosachharidases
Maltose, small polymer of glucose
Optimal pH 6.7
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12. 4
3 2
1 𝜶-AMYLASE
More powerful
Maltose & small polymer
of glucose
15-30 min
P-AMYLASE
S
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L
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DIGESTION OF CARBOHYDRATES

13. LACTOSE
g-POLYMER
MALTOSE
SUCROSE
GALACTOSE + GLUCOSE
FRUCTOSE + GLUCOSE
GLUCOSE + GLUCOSE
GLUCOSE * n𝜶-DEXTRINASE
MALTASE
SUCRASE
LACTASE
Final products of carbohydrate digestion are all monosaccharides
They are all water soluble and are absorbed immediately into the portal blood
Glucose represents more than 80 per cent of the final products of carbohydrate
digestion, and galactose and fructose each seldom more than 10%
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DIGESTION OF CARBOHYDRATES

14. STARCHES
GLUCOSE
MALTOSE AND 3-9 GLUCOSE
POLYMER
GALACTOSE
LACTOSE
FRUCTOSE
SUCROSE
Ptyalin-20-40%
Pancreatic amylase 50-80%
Maltase & 𝜶-dextrinase
Lactase Sucrase
S
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M
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DIGESTION OF CARBOHYDRATES

15. The characteristics of each protein are determined by
Proteins or polypeptides must be digested into their smaller
constituents before absorption
20 standard amino acids
In body, particularly the liver has substantial ability to
interconvert various amino acids subject to the body’s needs
Some amino acids, termed the essential amino acids,
cannot be synthesized by the body either de novo or from
other amino acids and thus must be obtained from the diet
DIGESTION OF PROTEINS

16. Amino acid
Neutral Acidic
Glutamate
Aspartate
Basic
Arginine
Lysine
Histidine
Aromatic
Tyrosine
Phenylalanine
Tryptophan
Aliphatic
Glycine
Alanine
Valine
Leucine
Isoleucine
imino
Proline
Hydroxyproline
Sulfur
Cystine
Methionine
Hydroxyl
Serine
Threonine
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O
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DIGESTION OF PROTEINS

17. pH:
Active: 2-3
Inactive: >5
AROMATIC AMINO ACID Initiate protein digestion
10-20% of total protein
digestion
Chief cells
Endopeptidase
High affinity- amino acid whose –COO end is provided by
aromatic Aa like tyrosine, tryptophan, phenylalanine, leucine
ENDOPEPTIDASE: ATTACK INTERNAL BOND LARGE POLYPEPTIDES
EXOPEPTIDASE: CLEAVE OFF ONE Aa EITHER END OF CARBOXY OR AMINO
TERMINAL
PEPSIN
S
T
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DIGESTION OF PROTEINS

18. S
M
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TRYPSIN
ELASTASE
CARBOXY-PEPTIDASE
CHYMO-TRYPSIN
Lysine , arginine
Hydrophobic amino acid
(Tyr, Trp, Phe, Met, Leu)
Alanine, glycine, serine
A
B
Valine, leucine, isoleucine, alanine
Arginine , lysine
30% free amino acid
70% oligopeptides (2-8 aa)
DIGESTION OF PROTEINS
P
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EXOPEPTIDASE

19. 1 AMINOPEPTIDASE
2 DIPEPTIDASE
TRI-PEPTIDE
DI-PEPTIDE
AMINO ACID
S
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P
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P
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DIGESTION OF PROTEINS
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P
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LARGE PEPTIDE
PEPSIN
Pancreatic
proteases

20. DIGESTION OF FATS
• FATS IN
DIET
‷ TRIGLYCERIDES
• CHOLESTEROL
• PHOSPHOLIPID
• CHOLESTEROL ESTER
• Vitamin K, D, E, A

21. DIGESTION OF FATS
3
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FOOD BEARING
LIPASES
GASTRIC LIPASE PANCREATIC
• Corpus & Fundus
• Optimum range pH
3-6
• Outer ester linkage
• Diglyceride & fatty
acid
• ACID LIPASES
• PHOSPHOLIPASE
• CARBOXY-ESTER
LIPASE
• PANCREATIC LIPASE-
COLIPASE
• PHOSPHOLIPASE-A2
• CHOLESTEROL ESTERASE

22. DIGESTION OF FATS
Bile salt inhibit its activity
which is
prevented by colipase
P
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Secreted in active form
Optimal pH range 8
1:1
5
3.5
C
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P
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Anchor lipase to fat water
interface in the presence
of bile salt
Procolipase
Positional specificity: cleaves 1 & 3 ester
linkage
P
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Proenzyme
Require bile salt for optimum activity
Hydrolyzed phospholipid at 2 position

23. DIGESTION OF FATS
CHOLESTEROL ESTERASE Hydrolyzed all 3 ester linkage of triglyceride
Also hydrolyzes ester linkage of fat soluble vitamins
Activity depends up on presence of specific bile salt -
Taurocholate & Taurochenodeoxycholate

24. DIGESTION OF FATS
1. SECRETION OF BILE ACID & VARIOUS LIPASES
2. EMULSIFICATION
3. ENZYMATIC HYDROLYSIS OF ESTER LINKAGE
4. SOLUBILIZATION OF LIPOLYTIC PRODUCTS WITHIN BILE SALT MICELLES

25. I
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Dietary fat
as large
triglyceride
droplets
EMULSIFICATION
Monoglyceride Free fatty acid
PL(Lecithin), Bile salt
Pancreatic lipase
micelles
DIGESTION OF FATS
1µm
4-7nm
Colipase