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What is the purpose of digestion?
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To prepare large biomolecules (proteins, lipids, polysaccharides) for absorption and transport
What is used to degrade large molecules for digestion?
Hydrolytic enzymes (hydrolases)
What is the mechanism of action for hydrolytic enzymes?
They cleave their substrates by the addition of a molecule of water
Proenzymes / Zymogens
Inactive precursors of digestive enzymes that are secreted from the pancreas
What are the 3 steps of turning proenzymes/zymogens into active enzymes?
Exist in granules near the cell membrane, in response to certain signals the granules fuse with the cell membrane
Contents of the granules are expelled into the lumen of the intestine
Activated when a part of the inactive precursor is proteolytically cleaved
Enteropeptidase / Enterokinase
Enzyme anchored to the epithelial cells of the small intestine, converts inactive trypsinogen into active trypsin
trypsin then activates other pancreatic proenzymes
What 3 zymogens does trypsin activate?
How does the zymogen pepsinogen get activated?
Pepsinogen has a small amount of enzyme activity and can activate itself to some degree in an acidic environment, active pepsin activates the remaining pepsinogen
Proteolytic Enzymes (Proteases)
Enzymes secreted by the stomach and pancreas to digest proteins into amino acids
An enzyme in the pancreas and saliva that cleaves polysaccharides into monosaccharides
Where does digestion first begin?
In the mouth where food is mechanically degraded into a slurry that is more readily attacked by hydrolytic enzymes
Saliva is secreted by what?
Saliva is an aqueous solution that contains what 6 components? What are their 2 main purposes?
Facilitate homogenization of food and lubricate the slurry so it can be swallowed:
To cleave alpha-1,4 glycosidic bonds
What produces the highly acidic environment in the stomach? What is the purpose of the environment?
Acid environment of the stomach is generated by H+-K+ ATPase to denature proteins and make them more susceptible to digestion by proteolytic enzymes (like pepsin)
Excessive acid generation causes what disease? How is it treated?
Can result in gastroesophageal reflux disease (GERD) that can be treated with H+-K+ ATPase inhibitors like omeprazole
A hormone that causes the release of sodium bicarbonate which neutralizes stomach acid
Hormone that stimulates the release of digestive enzymes from the pancreas and secretion of bile salts from the gallbladder
Movement of food from the stomach to the small intestine stimulates the secretion of what 2 hormones from small intestinal cells?
Small fragments of digested proteins
Enzymes on the surface of intestinal cells that cleave oligopeptides into amino acids and di- and tripeptides that are then conveyed into the intestinal cell by transporters
Where are many peptidases found?
Bound to the membrane, can also be found inside the cell
Transporter that releases amino acids from intestinal cells into the blood
At least how many transporters exist that bring amino acids and di- and tripeptides into intestinal cells?
Celiac Disease / Gluten Enteropathy
Genetically disposed people have an inflammatory response to gluten-derived peptides (wheat, rye, and barley) because they mimic immunostimulators
How is Celiac Disease characterized?
The inflammation damages the intestinal lining and impairs nutrient absorption which causes weight loss, diarrhea, and anemia
What is the frequency of Celiac Disease in caucasians?
1 in 250
Storage proteins in plants that provide amino acids and carbon, nitrogen, and sulfur for growth and development
What are the 2 gluten proteins in wheat?
What is the 1 gluten protein in barley and rye?
Gluten proteins are rich in what 2 amino acids?
Glutens are resistant to complete digestion by what 2 types of proteases?
Proteins that have high proline amino acid content, gluten is sometimes called prolamins
A rare defect in the transporter for tryptophan and other nonpolar amino acids; characterized by rashes, ataxia, delayed mental development, and diarrhea
What is our primary source of carbohydrates?
What are the products after alpha-amylase cleaves starch?
After alpha-amylase, what 2 enzymes complete the digestion?
What 3 things do alpha-glucosidase digest?
Any other oligosaccharides that wasn’t digested by amylase
What does alpha-dextrinase do?
Digests limit dextrin into simple sugars
Where are alpha-glucosidase and alpha-dextrinase found?
On the surfaces of intestinal cells
Enzyme that digests lactose (galactose+glucose)
Enzyme that digests sucrose (glucose + fructose)
What are the 2 transporters that transports monosaccharides into the intestinal epithelial cells? What is the transporter that releases monosaccharides into the bloodstream?
Sodium-glucose linked transport (SGLT) - secondary active transport process
GLUT5 - diffusion
GLUT2 - diffusion
What monosaccharide(s) do sodium-glucose linked transporters (SGLT) transport into the intestine? How about GLUT5?
SGLT: glucose and galactose
What do triacylglycerols form in the stomach?
What is the role of bile salts in lipid digestion?
Bile salts insert into the lipid droplets to make them more accessible to digestion by lipases
Enzymes secreted by the pancreas that convert triacyclglycerols into 2 fatty acids and monoacylglycerol
How are the digestion products of lipids carried to intestinal epithelium cells for absorption?
Carried as micelles
Lipoprotein transport particles
Describe the structure of chylomicrons
Approximately 200nm in diameter and composed of 98% triacylglycerols with proteins and phospholipid on the surface
How are fatty acids and monoacylglycerol transported into intestinal cells?
By membrane proteins like fatty-acid-binding protein (FABP)
What happens to the lipids once they are inside the intestinal cells?
Fatty-acid-transport proteins (FATP) bring them to cytoplasmic face of smooth endoplasmic reticulum (SER) where triacyclglycerols are reformed from free fatty acids and monoacylglycerol
Once triacylglycerols are reformed inside the intestinal cell, where do they go?
After transport into the lumen of the SER, the triacylglycerols associate with specific proteins and a small amount of phospholipid and cholesterol to form lipoprotein transport particles
Where do chylomicrons end up?
Are released into the lymph system and then eventually into the blood so that triacyclglycerols can be absorbed by tissues
Where will chylomicrons bind?
They bind to membrane-bound lipoprotein lipases
Where will chylomicrons bind? What happens?
Primarily at adipose tissue and muscle; triacylglycerols are degraded again into free fatty acids and monoacylglycerols for transport into the tissue, are resynthesized, and stored
Where can chylomicrons be oxidized? What does it provide?
In muscle and other tissues, can be oxidized to provide energy
Chylomicrons also function in the transport of what 2 things?
Responsible for the packing and unpacking of the vesicles; acts as a detergent to solubilize fats for absorption and is itself absorbed
Micelle formation is facilitated by what?
The structure of glycocholate resembles what?
Describe snake venom
A highly modified form of saliva, consists of 50 to 60 different protein and peptide components that differ among species of snake and possibly individuals of the same species
Rattlesnake venom contains what 3 digestive enzymes?
Proteases like collagenase
Other connective tissue digestive enzymes like hyaluronidase
What are the 2 functions phospholipases in snake venom?
Digest cell membranes at the site of the snakebite to cause a loss of cellular components and
A thin sheet of fibrous proteins, including collagen, that underlies the epithelial cells
What 2 things are degraded by proteolytic enzymes in snake venom? What is the outcome?
Components of the extracellular matrix
Leads to severe tissue damage
Some proteolytic enzymes in snake venom can stimulate what?
The formation of blood clots and enzymes that digest blood clots; depletes all clotting factors so clots can’t form
What is a neurotoxic effect snake venom can have on prey?
Can immobilize them
What are 3 pharmacological uses of snake venom? What species?
South african pit viper: hypertension drugs
Southeastern pigmy rattlesnake: reduce likelihood of heart attack
Copperhead: promising anticancer drug
What is the function of collagenase in snake venom?
Digests the protein collagen, a major component of connective tissue
What is the function of hyaluronidase in snake venom?
Digests hyaluronidase, a glycosaminoglycan component of connective tissue
How do snakes begin digestion?
They inject digestive enzymes into the prospective meal before consumption
A mixture of lipid droplets and water
Amphipathic molecules synthesized from cholesterol in the liver secreted from the gallbladder in response to cholecystokinin
What do bile salts do?
Enhance emulsification after lipids leave the stomach
When large amounts of fats (as much as 30g per day) are excreted in the feces because of inadequate production of bile salt due to liver disesase
What is steatorrhea named after?
Stearic acid, a common fatty acid
Energy meets what 3 fundamental needs
Muscle contraction: performance of mechanical work in muscle contraction and cellular movements
Active transport of molecules and ions
Synthesis of macromolecules and other biomolecules from simple precursors
Organisms that obtain energy by capturing sunlight
Organisms that obtain energy through the oxidation of carbon fuels
Molecules are degraded or synthesized stepwise in a series of reactions
ATP can be called (1) and is formed by (2)`
energy currency of life
the oxidation of carbon fuels
What is common to all metabolic pathways despite many reactions occurring inside a cell?
A limited number of reaction types that involve particular intermediates
Metabolic pathways are (1) regulated.
How are enzymes involved in metabolism organized?
Into large complexes