1: Introduction to Carbohydrates

Question 1

define monosaccharide, disaccharide, oligosaccharide, and polysaccharide

Answer 1

• monosaccharide
– 1 sugar residue (ex: glucose)

• disaccharide
– 2 sugars covalently bound together (ex: lactose,
sucrose, maltose, isomaltose)

• oligosaccharide
– 2-15 sugars covalently bound in a linear or branched chain (ex: α-dextrins)

• polysaccharide
– many sugars covalently bound in a linear or branched polymer (ex: glycogen, α-amylose, amylopectin)

Question 2

recognize glycosidic linkages (for example: α1,4 vs β1,4 vs α1,6, etc.)

Answer 2

alpha = trAns to CH2OH

Beta = cis

For numbers, count the carbons

See pg. 3 lecture 1 (not notes)

Question 3

recognize the structures (in cyclic form) of glucose, galactose, fructose, maltose, isomaltose, lactose, sucrose, maltotriose, α-dextrins, amylose, amylopectin, glycogen, and cellulose.

Answer 3

See pgs. 4 - 8

Question 4

list the major dietary carbohydrates

Answer 4

Main carbs:

Starch

Lactose = milk

Sucrose = table sugar

Question 5

describe how and where the major dietary carbohydrates are digested

Answer 5

Monosaccharides are transported into bloodstream via intestinal epithelial cells.

• Endoglycosidases (ex: α-amylase) cleave
internal glycosidic bonds in sugar polymers
• Exoglylcosidases (ex: glucoamylase) cleave terminal glycosidic bonds in sugar polymers
• Disacharidases (ex: maltase) cleave glycosidic bonds in disaccharides

Specificity of Glycosidases is based on structure of glycosidic linkage

Question 6

describe the causes of lactose intolerance and its treatment

Answer 6

Lactose intolerance = lactase deficiency

75% of ADULT world

• Undigested lactose moves to colon where bacteria digest it. Digestion products may cause diarrhea, nausea, abdominal cramps, bloating, and gas.

Lactose Intolerance - Treatment
•  Modification of diet to avoid dairy
•  Consuming lactase treated dairy
products
•  Taking lactase enzyme tablets prior to consuming dairy products

Question 7

discuss the basic functions of the major carbohydrate metabolism pathways (glycolysis,
citric acid cycle, gluconeogenesis, glycogen synthesis, glycogenolysis, and the pentose phosphate pathway) and their relationships to one another

Answer 7

see pgs. 16 - 21

Question 8

Why isn’t Cellulose digested?

Answer 8

We cannot digest Cellulose because we do not have an enzyme that can digest a glucose-glucose beta 1,4 linkage.

Question 9

Describe the roles and specificities of α-amylase and the various intestinal glycosidases involved.

Answer 9

• α-Amylase (endoglucosidase) in pancreas & saliva hydrolyzes random internal α1,4 bonds in STARCH. Glucoamylase also does a-1,4 but it is an exoglycosidase. Note that starch is the only sugar digested in mouth, rest in intestine.
• Carbohydrates must be cleaved to monosaccharides before they can be transported into epithelial cells.

• Epithelial cells synthesize and secrete glycosidases that remain attached to brush border
– they cleave oligosaccharides and disaccharides to monosaccharides.

• Monosaccharide transporters in brush border (apical membrane) move monosaccharides into cells
• Monosaccharide transporters in basolateral membrane move monosaccharides into bloodstream.

Review pgs 10 - 11.