Biochemistry Chapter 27
Learning Objectives
1.
What type of bond connects the glucosyl residues in amylose chains?
 α-1,4-glycosidic bonds link the residues into straight chains
2. What allows the chains to branch in amylopectin?
 α -1,6 glycosidic bonds allow amylopectin molecules to branch
3. Do starch blockers work as diet pills?
 Not currently, probably because of acid inactivation and compensatory amylase produciton
by the body
4.
What does salivary α-amylase produce?
 α-amylase is an endoglucosidase that randomly hydrolyzes α-1,4 bonds to make α-dextrins
5.
What does pancreatic α-amylase do? What kind of enzyme is it?
 Pancreatic α-amylase continues the salivary enzymes’ work, producing maltose, maltotriose,
and limit dextrins (branched, four to nine glucosyl unit oligosaccharides)
 It is an endoglucosidase
6.
How is isomaltose produced? What kind of enzyme is it?
 Glucoamylase is the terminal amylase, and it digests limit dextrin α-1,4 bonds until it reaches
a branch point, at which point it leaves isomaltose to be digested by other enzymes
 It is an exoglucosidase, which means it digests from the nonreducing end (-OH) of sugars
7. Where is glucoamylase located? Hint: besides the brush border!
 Glucoamylase tends to be located in the ileum (last chance)
8.


What produces glucose?
By glucoamylase (minor) and the sucrase-isomaltase complex only, in the brush border
[Sucrase-isomaltase complex includes sucrase-maltase and isomaltase-maltase]
9. What is trehalose?
 A rarely encountered sugar in Western diets that can cause nausea if trehalase is deficient
10. What is β-glycosidase complex?
 Bettern known as lactase-glucosylceramidase, it hydrolyzes the β-bond in lactose
 Different from other enzymes; attached by its carboxyl end with phosphatidylgylcan anchor
11. What do colonic bacteria make?
 Short chain fatty acids: acetic acid, propionic acid, butyric acid
 Gases—hydrogen in particular can be used in breath tests
 Lactate
12. What category of fiber do cellulose, hemicellulose, and lignins belong in?
 These are forms of insoluble fiber
13. In what category of fiber do pectin, mucilage, and gums belong?
 Soluble fiber
14. How much fiber do you need?
 14 g / 1000 kcal; both soluble and insoluble
15. How does the glycermic response differ from the glycemic index of a food?
 The glycemic response to ingested food depends on not just the glycemic index, but also the
fiber and fat content of the food as a whole, as well as its preparation
16. How is fructose absorbed from the gut?
 The GLUT-5 transporter uses facilitated diffusion to pick up primarily fructose. There is no
Na+ dependent transport for fructose
17. Name the glucose transporters for: neurons, BBB, erythrocytes, liver cells, & adipose/muscle
tissue
 GLUT3 Neurons
 GLUT1 BBB
 GLUT1 RBCs
 GLUT2 liver
 GLUT4 adipose and muscle
18. What types of cells are not dependent upon insulin for glucose uptake (4)?
 Neurons, liver, erythrocytes, and pancreatic cells do not rely on insulin
 Most notably, muscle and adipose tissue do rely on insulin to get glucose
19. How is glucose transported out of the intestines?
 Facilitated transport moves glucose from the lumen into the intestinal mucosa cells
 GLUT2 on the cells’ serosal surface moves glucose out, eventually into capillaries