NEG 8-10, Digestion and hormones Flashcards
(34 cards)
Protease
A protease is any enzyme that performs proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in a polypeptide chain.
Stomach protease: what is it, where is it secreted, how is it activated, and where does it cleave?
Pepsinogen, secreted by chief cells, activated to pepsin by HCL, and endopeptidase.
What are the proteases and their zymogens in the small intestine?
Trypsinogen -> trypsin
Chymotrypsinogen -> chymotrypsin
Proelastase -> elastase
Procarbxypeptidase -> carboxypeptidase
Where do peptidases of the small intestine come from and what activates their zymogen?
Small intestine, activated by zymogen.
Of the small intestine peptidases, which are enteropeptodases and which is a carboxypeptidase (terminal cleavage)?
Trypsin; endopeptidases
Chymotrypsin; endopeptidases
Elastase; endopeptidases
Carboxypeptidase; enteropeptodases
Trypsin; what type of amino acids does it cleave?
Basic amino acids
Elastase; what type of amino acids does it cleave?
Hydrophobic amino acids
Chymotrypsin; what type of amino acids does it cleave?
Small amino acids
Carboxypeptidase; what type of amino acids does it cleave?
Hydrophobic and basic terminal amino acids.
Where are carbohydrates digested?
Stomach and small intestine
Alpha-amylase; where is it produced, what does it do, and what deactivates it?
Produced in salivary glands, hydrolyzes glycosidic bonds, and deactivated by low pH in stomach.
Brush border enzymes
Enzymes that are anchored on the microvilli of the brush border. Includes: Sucrase Maltase Lactase Trehalase Aminopeptidase Carboxypeptidase
Products of carbohydrate digestion
Glucose
Fructose
Galactose
Brush border
A brush border is the microvilli-covered surface of simple cuboidal epithelium cells found in the small/large intestine and kidney..
Enterocyte
Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells found in the small intestine. Microvilli on the surface increase surface area for the digestion and transport of molecules from the intestinal lumen. The cells also have a secretory role.
Where does most absorption occur?
Most absorption occurs in the proximal small intestine. Almost all digestion occurs by the time the chyme reaches the jejunum.
Peptide vs amino acid absorption into enterocyte
Peptides: Accounts for the the majority of protein absorption and occurs more rapidly. Symported into cell with H+, the gradient of which is maintained by Na/H antiporter. Peptides are then metabolized fully into free amino acids within the enterocyte.
Amin Acids: Occurs slower and is energy dependent. Amino acid symported inside enterocyte with Na. The Na gradient is maintained by Na/K ATPase.
Basolateral membrane
The side of a cell that is facing ETC or other cells, rather than the tubular side (lumen).
Lumen
Lumen, meaning “an opening”; is the inside space of a tubular structure, such as an artery or intestine.
Transport of amino acids across the basolateral membrane
Released into ETC by facilitated diffusion and co-transport, where it is transported by the hepatic vein to the portal artery. Glutamate and aspartame, however, are used for energy in by the enterocyte.
Absorption of monosaccharides into enterocyte
Facilitated diffusion:
SLGT1
GLUT5
Alternatively it can be done by passive diffusion but this process is slow.
SGLT1
Na/Glucose linked transporter.
Transports glucose from lumen to enterocyte. One glucose enter with 2 Na moving with concentration gradient. Na gradient maintained by Na/K ATPase.
GLUT5
Fructose Transporter from lumen to enterocyte.
Emulsification
An important aspect of lipid digestion. Emulsification is the clustering of immiscible lipid in polar water. Mastication breaks down fats into small drops, allowing access by enzymes.
