Enzyme

Amylase Lipase Protease

A. Substrate polysaccharide emulsified fat dipeptide or polypeptide

B. Substrate emulsified fat dipeptide or polypeptide polysaccharide

C. Product amino acids small polysaccharides or monosaccharides

fatty acids and glycerol

D. Product small polysaccharides or monosaccharides

amino acids fatty acids and glycerol

1. Which of the following is correct regarding the enzymes listed in the table?

2. Figure 1 below shows a cross-section through the small intestine and Figure 2 an enlarged longitudinal section through a single villus.

Using these diagrams, outline three ways in which the structure of the small intestine is related to its function of absorbing food.

(3 mks)

Figure 1 Figure 2

1. A

2. villus intestinal wall has many folds to increase surface area ( : volume ratio);surface of villus close to blood vessels so materials can easily diffuse;surface of villus close to lymph vessels so lipids can be easily absorbed;greater surface area related to greater rate of diffusion;

villus wall consists of single layer of cells;3 max

Do not accept microvilli – not visible in diagrams.

The intestinal wall of the villus has many folds to increase surface area, or the SA:Vol. This increased surface area is related to an increased rate of diffusion. Aiding in diffusion is the fact that the wall of the villus consists only of a single layer of cells. The surface of the villus itself is located close to the blood vessels, so that materials can easily diffuse into them. It is also located close to the lymph vessels, so that lipids can easily be absorbed.

Enzyme

Amylase Lipase Protease

A. Substrate polysaccharide emulsified fat dipeptide or polypeptide

6.1 Digestion6.1 Digestion

6.1.1 6.1.1 ExplainExplain why digestion of why digestion of large food molecules is essential.large food molecules is essential.

• Most food molecules are large polymers & insolubleMost food molecules are large polymers & insoluble• Too big to pass through membrane or into bloodToo big to pass through membrane or into blood

• Must be digested Must be digested smaller , soluble molecs smaller , soluble molecs absorbed to bloodabsorbed to blood• Series of chem reactions Series of chem reactions smaller & smaller molecules smaller & smaller molecules

• ProteinProtein amino acids amino acids• ExampleExample: you eat egg : you eat egg albumin (egg white) contains amino albumin (egg white) contains amino

acid serine acid serine hydrolysis reactions break down prtn into aa’s hydrolysis reactions break down prtn into aa’s serine absorbed @ small intestine serine absorbed @ small intestine capillary, bloodstream capillary, bloodstream pancreas cell pancreas cell Transcription/Translation Transcription/Translation used to make used to make a new protein hormone insulin moleculea new protein hormone insulin molecule

• LipidsLipids (triglycerides) (triglycerides) glycerol, fatty acids glycerol, fatty acids• CarbsCarbs (poly/di/monosaccharides) (poly/di/monosaccharides) monosaccharides monosaccharides• Nucleic acids Nucleic acids (DNA/RNA) (DNA/RNA) nucleotides nucleotides

• THENTHEN, can be absorbed through cells of dig. system and blood, can be absorbed through cells of dig. system and blood• Circulatory sys transports nutrients to body cellsCirculatory sys transports nutrients to body cells• Body uses to make your “own” DNA, protein, etc.Body uses to make your “own” DNA, protein, etc.

6.1.2 6.1.2 ExplainExplain the need for enzymes in digestion. the need for enzymes in digestion.

• Enzymes = biol catalysts, Enzymes = biol catalysts, increase rate of reactionincrease rate of reaction• Increase rate of digestion at Increase rate of digestion at body temperaturebody temperature!!

• Activation energy reduced: normal rxn – higher act Activation energy reduced: normal rxn – higher act energy –higher body temp----not possible in humans!energy –higher body temp----not possible in humans!

• Digestive enzymes Digestive enzymes specificspecific for specific food types for specific food types• Secreted into lumen of gutSecreted into lumen of gut

• HydrolysisHydrolysis of insoluble food molec into soluble products of insoluble food molec into soluble products• Break down macromoleculesBreak down macromolecules

• Starts @ mouth—salivary amylaseStarts @ mouth—salivary amylase• Starch (amylose) Starch (amylose) maltose maltose glucose glucose

6.1.3 6.1.3 StateState the source, substrate, products and the source, substrate, products and optimum pH conditions for one amylase, one optimum pH conditions for one amylase, one protease and one lipase.protease and one lipase.

• Any human enzymes can be selected. Details of structure or Any human enzymes can be selected. Details of structure or mechanisms of action are not required.mechanisms of action are not required.

• Pancreatic amylase:Pancreatic amylase:• SourceSource: pancreas cells: pancreas cells• Optimal pH Optimal pH 7.5 – 7.87.5 – 7.8• SubstrateSubstrate: starch (amylose): starch (amylose)• End productEnd product: maltose (disaccharide): maltose (disaccharide)• ActionAction: hydrolysis of 1-4 glycosidic bonds: hydrolysis of 1-4 glycosidic bonds

6.1.3 State the source, substrate, products and 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one optimum pH conditions for one amylase, one protease and one lipase.protease and one lipase.

• PepsinPepsin: (a protease): (a protease)• SourceSource: stomach cells: stomach cells• Optimal pH Optimal pH 2 - 32 - 3• SubstrateSubstrate: polypeptide chains of amino acids: polypeptide chains of amino acids• End productEnd product: amino acids: amino acids• ActionAction: hydrolysis of peptide bonds: hydrolysis of peptide bonds

6.1.3 State the source, substrate, products and 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one optimum pH conditions for one amylase, one protease and one lipase.protease and one lipase.

• Pancreatic lipase:Pancreatic lipase:• SourceSource: pancreas cells: pancreas cells• Optimal pH Optimal pH 77• SubstrateSubstrate: triglyceride lipid: triglyceride lipid• End productEnd product: glycerol & fatty acid chains: glycerol & fatty acid chains• ActionAction: requires bile salts to emulsify lipids : requires bile salts to emulsify lipids

(increases SA of lipid, for fat digestion, exposes (increases SA of lipid, for fat digestion, exposes glycerol structure to enzymeglycerol structure to enzyme• Hydrolysis of ester bonds b/w glycerol and fatty Hydrolysis of ester bonds b/w glycerol and fatty

acidsacids

6.1.4 6.1.4 DrawDraw and and labellabel a diagram of the a diagram of the digestive system.digestive system.

• ““Alimentary Canal”Alimentary Canal”

• mouth, esophagus, mouth, esophagus, stomach, small intestine, stomach, small intestine, large intestine, anus, liver, large intestine, anus, liver, pancreas and gall bladder.pancreas and gall bladder.

• The diagram should The diagram should clearly clearly showshow the the interconnectionsinterconnections between these between these structures!!!!!structures!!!!!

6.1.5 6.1.5 OutlineOutline the the functionfunction of the of the stomach, small intestine and large stomach, small intestine and large intestine.intestine.

1. 1. StomachStomach: @ end of esophagus (: @ end of esophagus (peristalsisperistalsis, muscular), muscular)Stores food, begins protein digestion. Stores food, begins protein digestion. (a) Lumen: (a) Lumen: mixes food mixes food w/gastric juice w/gastric juice (pepsin, HCl, mucus)(pepsin, HCl, mucus)(b) (b) Gastric pits: Gastric pits: mucusmucus , , enzymesenzymes and and acidacid are secreted are secreted

(c) Mucus secreting cells. ((c) Mucus secreting cells. (protectprotect surface of stomach from auto- surface of stomach from auto-digestiondigestion))

(d) Parietal cells: produce (d) Parietal cells: produce HClHCl which kills microorganisms that enter which kills microorganisms that enter the digestive system (food & tracheal mucus). This also converts the digestive system (food & tracheal mucus). This also converts inactive inactive pepsinogenpepsinogen to active pepsin & helps degrade foods some. to active pepsin & helps degrade foods some.

(e) Chief cells: produces pepsinogen (protease enzyme(e) Chief cells: produces pepsinogen (protease enzyme) activated by HCl pepsin, most active in acidic pH

6.1.5 6.1.5 OutlineOutline the function of the stomach, the function of the stomach, small intestine and large intestine.small intestine and large intestine.

2. small Intestine: 2. small Intestine: wherewhere digestion is completed digestion is completed & products of & products of digestion are digestion are absorbedabsorbed into the blood stream into the blood stream

Duodenum: Duodenum: bilebile from liver/gall bladder from liver/gall bladdertrypsintrypsin (protease), (protease), lipaselipase, , amylaseamylase, , bicarbonatebicarbonate from from pancreaspancreas

Small molecules Small molecules absorbedabsorbed1000s of 1000s of villivilli (each w/cap bed and lacteal) increase Sfc Area (each w/cap bed and lacteal) increase Sfc Area

Most molecules Most molecules absorbedabsorbed @ cap bed @ cap bedLipids absorbed @ Lipids absorbed @ lacteallactealTo body cells via another To body cells via another capillarycapillary & used for energy or building & used for energy or building new macromolecules (new macromolecules (assimilationassimilation))

(a) Villus: increase SA for absorption of products of digestion(a) Villus: increase SA for absorption of products of digestion(b) Microvilli: border of epithelial cell, increase the SA for absorption. (b) Microvilli: border of epithelial cell, increase the SA for absorption. (c) Lacteals connect to lymphatic system for the transport of lipids(c) Lacteals connect to lymphatic system for the transport of lipids(d) In the wall of the small intestine are the blood vessels to transport absorbed products to the general (d) In the wall of the small intestine are the blood vessels to transport absorbed products to the general

circulation, And muscles to maintain peristalsiscirculation, And muscles to maintain peristalsis

6.1.5 Outline the function of the 6.1.5 Outline the function of the stomach, small intestine and large stomach, small intestine and large intestine.intestine.

3. Large Intestine or colon: 3. Large Intestine or colon: responsible for reabsorption of responsible for reabsorption of water from gut.water from gut.

Undigested food Undigested food (unabsorbed) excreted(unabsorbed) excreted

WaterWater we drink/eat – much is we drink/eat – much is reabsorbedreabsorbed, some passes, some passes

E. coliE. coli (mutualistic) synthesize (mutualistic) synthesize Vitamin K Vitamin K for us!for us!

(a) The lumen of the colon(a) The lumen of the colon

(b) The mucus producing goblet cells(b) The mucus producing goblet cells

(b) Muscular walls to maintain peristalsis(b) Muscular walls to maintain peristalsis

6.1.6 Distinguish between 6.1.6 Distinguish between absorption and assimilation.absorption and assimilation.

Insoluble food molecules are digested to soluble Insoluble food molecules are digested to soluble products in the lumen of the gut.products in the lumen of the gut.

AbsorptionAbsorption::• soluble products are 1soluble products are 1stst taken up by various taken up by various

mechanisms into epithelial cells lining mechanisms into epithelial cells lining gutgut. . • These cells then load various These cells then load various absorbedabsorbed

molecules into blood stream. molecules into blood stream.

AssimilationAssimilation::• soluble products of digestion then transported soluble products of digestion then transported

to to various tissues various tissues by circulatory system. by circulatory system. • cells of tissues then absorb molecules cells of tissues then absorb molecules for use for use

within tissues within tissues

6.1.7 Explain how the structure of the villus is 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of related to its role in absorption and transport of the products of digestion.the products of digestion.

• structure structure increases SA increases SA for for absorptionabsorption of digested food molecules of digested food molecules into circ/lymph systems for transportinto circ/lymph systems for transport

• Digested nutrients from lumen of small int pass through Digested nutrients from lumen of small int pass through single-cellsingle-cell thickness of villus epithelium to get to cap bed or lactealthickness of villus epithelium to get to cap bed or lacteal

• Undigested nutrients can’t pass throughUndigested nutrients can’t pass through• Blood/lymph from arteriole/lacteal enters villus, picks up nutrients, Blood/lymph from arteriole/lacteal enters villus, picks up nutrients,

leaves via venule/lactealleaves via venule/lacteal(a) folds increase SA:VOL ratio by X 3(a) folds increase SA:VOL ratio by X 3

(b) Villi project into the lumen of the gut increasing the surface area by X 10(b) Villi project into the lumen of the gut increasing the surface area by X 10

(c) Microvilli are outward folds of the plasma membrane increasing the surface area another (c) Microvilli are outward folds of the plasma membrane increasing the surface area another X10X10

6.1.7 Explain how the structure of the villus is 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of related to its role in absorption and transport of the products of digestion.the products of digestion.

• Blood supply in villus Blood supply in villus absorbs end products absorbs end products of of digestion from epithelial cells digestion from epithelial cells

• lacteals receive lipoproteins before transporting to lacteals receive lipoproteins before transporting to circulatory system. circulatory system.