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Biochemistry Chapter 27 Questions
What dietary sugar is found in fruit juice and sweets? What happens if it cannot be
absorbed?
a. Sucrose. If it cannot be digested or fructose cannot be absorbed, fructose is
converted to gas by colonic bacteria.
What carbohydrate monomer (s) are amylose, amylopectin, sucrose, maltose, and lactose
comprised of? What polymer in plants is part of our dietary fiber?
a. Amylose is α14 linked chain of glucose molecules
b. Amylopectin contains amylose chains with some α16 branching
c. Sucrose is a α12 disaccharide of fructose and glucose
d. Lactose is a β14 link between galactose and glucose
e. Maltose is the disaccharide in amylase α14 link of 2 glucose molecules
f. Plant polymer we can’t digest is lignan
What enzyme breaks glycosidic bonds? What is it specific for?
a. Glycosidase specific for sugar, type of bond (α vs β) and number of saccharide
units
What is a starch blocker? Why were they ineffective in weightloss?
a. Protein initially found in beans that inhibits α- amylase. Ineffective for one of
several potential reasons: inactivated by stomach acid or the amount ingested
was not enough to block the body’s amylase activity
What type of bonds do amylases cleave? What are products of salivary α-amylase? How
about of pancreatic α- amylase?
a. α 14 glucose to glucose bonds; CANNOT break α 16 glucosyl bonds
b. salivary amylase: random cleavages producing α-dextrins
c. pancreatic amylase: maltose, isomaltose (2 glucoses with α 16
linkage)maltriose, and oligosaccharides w/ 4-9 glucosyl residues known as limit
dextrins
What conditions can reduce pancreatic secretions? Will this make amylase a rate
limiting step of carbohydrate metabolism?
a. Alcohol induced pancreatitis, surgical removal of pancrease, or cystic fibrosis
b. Not likely. Even at only 10% normal levels, it is not rate limiting.
What are 4 glucosidades found in the intestinal brush border?
a. Glucoamylase, sucrose-isomaltase, trehalase, and lactase-glucosylceramidase
What can glucoamylase (an exoglucosidase) act on? What are its products
a. Acts on limit dextrins and poly saccharides; it can break down α 14 bonds and
can produce isomaltase or glucose
What enzymatic activity is the sucrase-isomaltase complex responsible for?
a. 100% sucrose digestion; almost 100% α 16 bond breakage (isomaltase); 80%
maltase digestion (other 20% from glucoamylase activity)
10. What are ppl w/ a genetic deficiency of the sucrase-isomaltase complex unable to
digest?
a. Sucrose. Glucoamylase and residual activity of sucrase-isomaltase are able to
allow for normal starch digestion.
11. What type of bond does trehalase act on? Where do you find trehalose (food source)?
a. α 11 link b/t the anomeric carbons of 2 glucose molecules
b. found in insects, mushrooms, algae, and other fungi
12. What type of bond does β-glycosidase act on (aka lactase-glucosylceramidase)?
a. β 14 bond b/t galactose and glucose (lactose) and the bond between either a
glucose or galactose and a ceramide in glycolipids
13. Where in the intestine are pancreatic α-amylase, sucrase-isomaltase, glucoamylase, and
β-glucosidase active?
a. Pancreatic α-amylase: duodenum
b. Sucrase-isomaltase and β-glucosidase: jejunum
c. Glucoamylase: activity progressively increases along track; strongest in ileum
14. How can you test for a problem in sugar digestion? (ie. pain after drinking fruit juice)
a. A hydrogen breath test. A combination of a portable measurer of H2 gas and a
non-portable gas chromatography machine are used to asses if there is H2 on
the breath. If a person is not absorbing a sugar, it is digested by intestinal
bacteria producing hydrogen gas.
15. What 2 things can cause lactose intolerance?
a. Nonpersistant lactase phenotype (primary lactose intolerance) (b/c don’t have
much dairy in diet; esp. Asians) and intestinal injury (secondary intolerance)
16. Why does a person w/ lactose intolerance get diarrhea and bloating?
a. The lactose can be converted to lactic acid, H2, and methane gas (CH4) by
colonic bacteria. Result: lactic acid along w/ lactose in stool causes osmotic
gradient pulling water into stools and producing diarrhea. The gas produced can
cause the bloating.
17. What types of fiber are insoluble? How about Soluble? Importance of fiber?
a. Insoluble: cellulose, hemicelluloses, and lignin
b. Soluble: pectins, gums, and mucilages
c. Bacteria can digest some soluble fibers providing nourishment for intestinal cells
an up to 10% of our total calories. Also, fiber softens stools reducing pressure
out on intestinal wall and hence lowers risk of diverticular disease.
18. Why can fiber be beneficial to a diabetic? Why would pasta and rice be better choices
for Ann Sulin than potatoes?
a. Dietary fiber slows the rate of absorption of monosaccharides from the
intestines. Pasta and rice have lower glycemic indices, so consumption of these
foods would result in slower entry of glucose into the blood than the potatoes
with a high glycemic index
19. What are 2 differences between facilitative glucose transporters and Na+ dependent
transporters of glucose?
a. Na+ dependent transport glucose against its concentration gradient, while
facilitative transporters have glucose moving down its conc. gradient
b. Na+ dependent are found on the luminal side of the intestinal membrane, while
facilitative are often found on the serosal side (blood vessel side)
20. Where are GLUT 1, GLUT 2, GLUT 3, GLUT 4, and GLUT 5 found? Why is 5 unique?
a. GLUT 1- RBCs, Blood brain barrier (BBB), Blood retinal barrier, blood-placenta
barrier, blood-testes barrier
b. GLUT 2- Liver, Kidney, Pancreatic β cells, serosal side of intestinal mucosa
c. GLUT 3- Brain (neurons)
d. GLUT 4- Adipose tissue, skeletal muscle, and heart muscle
e. GLUT 5- Intestinal epithelium and spermatozoa (unique b/c transports fructose)
21. Why does the liver have a high Km for glucose transport?
a. Because it is the regulator for glucose. Hence when glucose levels start to fall,
the high Km means that the liver’s levels of glucose will go down before other
tissues. When this happens the liver will trigger glycolytic pathways and
gluconeogenisis to increase glucose.
22. Why is glucose transport through the BBB slow?
a. Because it has very tight junctions (not leaky), so glucose MUST go through GLUT
1 transporter and at low concentrations this transport may be slow.
23. How does insulin act on tissues (muscle, adipose) to increase its uptake of glucose?
a. It causes vesicles containing GLUT 4 receptors to fuse with the serosal
membrane so that glucose can flow into tissue, when levels are high in blood,
down its concentration gradient.
24. How does cholera cause diarrhea? How do you treat it?
a. It binds a ganglioside receptor on the cell surface leading to increased cAMP. The
increased cAMP causes normal absorption of sodium, anions, and H20 to be
diminished and causes intestinal crypt cells to secrete chloride ions.
b. Cholera doesn’t affect the Na+ glucose transporters, so you give the patient
increased glucose and sodium (also a. a.) that they can absorb. When they
absorb these, water goes with the solute leading to water reabsorption. May
also need to give an antibiotic