Chapter 14: Digestion Flashcards
Digestion is facilitate by a diverse set of which enzymes
Hydrolytic enzymes
All products from the breakdown of biomolecules are finally converted to….
Acetyl CoA
Components and characteristics of Acetyl-CoA
Acetyl (COCH3) : 2 C
CoA (Coenzyme A): Serves as a carrier
Will enter the citric acid cycle to make energy
Digestion in Mouth
- Where digestion begins
- Chewing —-> Slurry
- The slurry is more readily attacked by hydrolytic enzymes
- Saliva contains: Na+, K+, Cl-, HCO3- and mucoproteins
Digestion in Stomach
- Site of food breakdown
- Chemical breakdown of protein begins
- Delivers Chyme to small intestine
- Acidic environment generated by H+/K+ ATPase
- Gastric amylase and Gastric lipase (initiate emulsification) have minor roles for other nutrients.
Enzyme involved in protein breakdown in stomach
Pepsin (active form) - immune to denaturation in high acidic solutions
Pepsinogen (inactive form)
- endopeptidase activated pepsinogen
Zymogen
- inactive enzyme or inactive precursor
- also called pro-enzymes
- get activated in site of digestion
- Allows control of the location of digestion —> i.e. compartmentalization
Exocrine role of Pancreas
- Extensive biochemical breakdown
- Secretes pancreatic enzymes/proenzymes
Endocrine role of Pancreas
- Coordinate whole body tissue response to feeding
- Secretes hormones
- Insulin with feeding ( high blood glucose levels)
- Glucagon when not fed (low blood glucose levels)
The Pancreas secretes…..
bicarbonate to neutralize stomach acid
Enteropeptidase
- Also called enterokinase
- Produced in the intestine to activate pancreatic enzymes
Role of small intestine
Digestion:
- Site of action for pancreatic enzymes
- Brush border enzymes
Absorption:
- Massive surface area via villi and microvilli
- intestinal tract lines with epithelial cells also called enterocytes
Secretin
- Stimulates pancreas to release sodium bicarbonate in intestine (neutralize the acidity of products entering)
Cholecystokinin (CCK)
- Stimulates pancreas to release digestive enzymes
- Stimulates the gall bladder to secrete bile salts
Protein digestion
- digested into oligopeptides
- Peptidases on surface of intestinal cells cleave oligopeptides
- a.a are subsequently released into blood by antiporters
Celiac Disease
- gluten enteropathy -> intestinal inflammatory disorder
- Genetically predisposed
- Mount an inflammatory response to gluten derived peptides found in Rye and Barley.
- Gluten proteins and rich in glutamine and proline –> may be linked to pattern of peptides produced during digestion
- Inflammatory response damages the intestinal lining –> impairs nutrient absorption
Carbohydrate Digestion
- Breakdown to monosaccharides inside the gut lumen and at enterocyte surface
- Sucrose and lactose digested by sucrase and lactase
- Galactose, glucose and fructose absorbed into enterocyte via transporters
which bonds do a-amylase , a-glucosidase and a-dextrinase cleave
a- amylase : cleaves a-1,4 bonds in starch and glycogen
a-glucosidase: ‘maltase’, cleaves a-1,4 bonds in starch and glycogen
a-dextrinase: cleaves a-1,6 bonds (debranching enzyme)
Bile Salts…
insert into lipid droplets rendering them more accessible to digestion by lipases
Lipases,….
convert the triacylglycerols into 2 fatty acids and monoacylglycerol
- digestion products are carried as micelles to intestinal epithelium
Examples of emulsification for fat digestion
- body temperature and peristalsis
- salivary and gastric lipase release fatty acids that act as surfactants
- Carboxy end interacts with water
- Bile salts
Chylomicron description
- lipoprotein
- transport particles
- exterior: phospholipid monolayer, apoproteins (ApoB-48) and cholesterol
- interior: TAGs and Cholesterol esters
