Nutrient Digestion 1 (Carbs + Proteins) Flashcards
Which term describes the following molecules: Starch, Cellulose and Glycogen
They are all Complex Carbohydrates
Describe the structure of Starch
▷Plant storage form of Glucose (ie. glycogen equivalent in plants)
▷Made up of two structures: a-amylose (glucose linked in straight chains), and amylopectin (glucose chains highly branched)
Describe the structure of Cellulose
▷Constituent of Plant Cell Walls
▷Unbranched, linear chains of glucose monomers linked by b-1,4 glycosidic bonds
Describe the structure of Glycogen
▷ Animal storage form of Glucose
▷Glucose monomers joined together by a-1,4 glycosidic bonds
Describe the enzymatic breakdown of Starch, Cellulose and Glycogen
▷Starch and Glycogen are broken down by amylases present in Saliva and the Pancreas -> they hydrolyse a-1,4 glycosidic bonds
▷Cellulose is not enzymatically broken down in vertebrates -> requires cellulase present in bacteria
Describe the breakdown of the following disaccharides: Maltose, Sucrose and Lactose
▷Maltose -> breakdown product of Starch and Glycogen -> broken down into 2 glucose molecules by Maltase
▷Sucrose -> broken down into one glucose and one fructose by Sucrase
▷Lactose -> broken down into one glucose and one galactose by lactase
What are the 2 Types of Transport across intestinal cell walls?
▷Transcellular -> through the cell (ie. monosaccharides)
▷Paracellular -> between the cells, across the tight junctional complex (ie. water molecules)
How is Glucose and Galactose absorbed into enterocytes?
▷Na+/K+-ATP-ase is expressed in the basolateral membrane of the Enterocyte -> 2 K+ in and 3 Na+ out -> maintains electrochemical gradient
▷SGLT-1 (Na+-coupled Glucose Transporter 1) -> binding site for 1 glucose and 2 Na+ molecules -> Secondary Active Transport
(glucose gets into the cell against it’s conc. gradient using the large electrochemical gradient of Na+, which is created by the primary active transport process (Na+/K+-ATP-ase))
How do Glucose, Galactose and Fructose get out of enterocytes into the blood stream?
Via GLUT-2 transporters -> Facilitated Diffusion!
How is Fructose absorbed into enterocytes?
Why is Fructose absorption not associated with water uptake?
▷Via GLUT-5 transports -> Facilitated Diffusion!
▷Because it doesn’t require Na+ to get into cells (unlike Glucose and Galactose ((NB. Oral Rehydration Therapy contains both salt, glucose and water!))
What are Peptidases?
Enzymes that hydrolyse peptide bonds and reduce proteins or peptides to amino acids
What are the 2 types of Peptidases?
▷Aminopeptidases -> cleaves amino end of proteins/peptides
▷Carboxypeptidases -> cleaves carboxy end of proteins/peptides
How are Amino Acids absorbed into enterocytes?
▷Na+/K+-ATP-ase is expressed in the basolateral membrane of the Enterocyte -> 2 K+ in and 3 Na+ out -> maintains electrochemical gradient
▷SAAT-1 (Na+-coupled Glucose Transporter 1) -> Secondary Active Transport
(we use the large Na+ E.C gradient to get AAs into the cell, which is created by the primary active transport process (Na+/K+-ATP-ase)) -> NB. a way of getting water into ur body bc it is a Na+-dependent process!! (not as big as glucose though)
How are Amino Acids absorbed out of enterocytes into the bloodstream?
Via a specific AA carrier -> Facilitated Diffusion!! (different carrier for different AA group)
How are small Di- and Tri- Peptides absorbed into enterocytes?
▷Na+-K+-ATP-ase -> maintains large Na+ E.C. gradient necessary for NHE3 (amongst other transporters*
▷NHE3 (Sodium-Hydrogen Anti-porter) -> Secondary Active Transport -> uses Na+ E.C gradient to pump H+ ions out of the cell -> maintains acidic small intestinal brush-border environment compared to small intestinal lumen (pH 6 vs. pH 7) -> necessary for small peptide absorption
▷PEP T1 (Peptide Transporter 1) -> uses Hydrogen ion transport (from metabolism) to get small peptides into cells (maintained by NHE3)
