Nutrition and Digestion (CHO + PROTEIN) Flashcards
Monosaccharides definition
hexose sugars (6C) - breakdown products of complex CHOs which are absorbed by the small intestine
Monosaccharide examples
glucose, galactose, fructose
Disaccharides definition
two monosaccharides linked together by glycosidic bonds
How are disaccharides broken down
broken down into constituent monomers by brush border enzymes of the small intestine
Lactose is broken down into
glucose + galactose using lactase
Sucrose is broken down into
glucose + fructose using sucrase
Maltose is broken down into
glucose + glucose using maltase
Disaccharide examples
lactose, sucrose, maltose
Polysaccharides definiton
long chains of monosaccharide units linked together by glycosidic bonds
Polysaccharide examples
starch, cellulose, glycogen
Starch definition
- plant storage form of glucose
- two types: a-amylose and amylopectin
- linked by a-1.4 glycosidic bonds
a-amylose chains are
straight chains of glucose
amylopectin chains are
highly branched chains of glucose
a-1,4 glycosidic bonds (starch, glycogen) are hydrolysed by what enzyme
amylases (some from saliva, most from pancreas)
cellulose definition
- constituent of plant cell walls
- unbranched linear chains of glucose monomers
- linked by B-1,4 glycosidic bonds
can the B-1,4 glycosidic bonds in cellulose be enzymatically digested
no, it is a dietary fibre - requires cellulase which is found in bacteria
glycogen definition
- animal storage form of glucose
2. glucose monomers linked by a-1,4 glycosidic bonds
Polysaccharides are broken down by amylases into
disaccharides
sucrose, maltose and lactose are all
oligosaccharidases
Enterocyte definition
intestinal absorptive cells - simple columnar epithelial cells found in the small intestine
How do glucose and galactose get into the cytoplasm of enterocytes
sodium-glucose co-transproters (SGLT-1) that are found on the apical surface of enterocytes
How does fructose get into the cytoplasm of the enterocyte
uses GLUT5 to cross the apical membrane (facilitated diffusion)
How do glucose and galactose exit the enterocyte to get into the blood stream
uses GLUT2 to exit via the basolateral membrane
facilitated diffusion
How does fructose exit the enterocyte to get into the blood stream
uses GLUT2 to exit via the basolateral membrane
facilitated diffusion
How does the sodium-glucose co-transporter (SGLT1) work
- NaK pump on the basal membrane pumps 2K in and 3Na out
- Does this via energy from hydrolysis of ATP
- This ATPase maintains small -ve electric potential in cell
- Electrogenic and osmotic Na+ gradient (from NaK pump and ATPase) in the cell used to transport monosaccharides out
Protein definition
polymers of amino acids linked together by peptide bonds - can vary in length
Peptides definition
small proteins, 3-10 amino acids in length
addition of CHO to a protein creates
glycoprotein
addition of a lipid to a protein creates
lipoprotein
proteases
enzymes which hydrolyse peptide bonds and reduce proteins into amino acids
peptidases
enzymes which hydrolyse peptide bonds and reduce peptides into amino acids
How do amino acids enter into enterocytes
enter at the apical membrane along with Na+ using co-transpoters (SAAT1)
How do amino acids exit the enterocyte and get into the blood stream
enter the circulation via selective channels in the basolateral membrane
