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Flashcards in Carbohydrates Deck (19)
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1

____ form of sugars is the predominant form in humans

D-form of sugars

2

contrast aldoses and ketoses

  • aldoses have an aldehyde group on C1 whereas ketoses have a keto group on C2

3

name 3 conditions where sugars are present in urine

  1. diabetes mellitus
  2. fructosuria and hereditary fructose intolerance
  3. galactosemia

Lactose intolerance patients do not have sugars in urine

4

name the C-4 epimers

glucose and galactose

5

name the C-2 epimers

glucose and mannose

6

describe sorbitol

  • sugar alcohol formed from glucose
  • formed in the nerve tissues, retina and the lens of the eye when the blood glucose is elevated (prolonged hyperglycemia in diabetics)

7

describe galactitol

galactitol is formed from galactose in the lens in children with untreated galactosemia

8

describe glucuronic acid

  • glucuronic acid is derived by oxidation of C-6 of glucose 
  • UDP-glucuronic acid is used in conjugation rxns (bilirubin, steroids)
  • glucuronic acid is a component of GAGs (hyaluronic acid, heparin) and contributes to the negative charge 

9

name the aldoses and ketoses

10

describe lactose

  • disaccharide made up of 2 monosaccharides linked by a glycosidic linkage
    • galactose + glucose linked by B1->4 glycosidic linkage
  • lactose is a reducing sugar (positive Benedict's test)

11

describe sucrose

  • glucose + fructose
  • non-reducing sugar since the C1 of glucose and C2 of fructose are involved in the glycosidic linkage (aldehyde and keto groups are not free)

12

describe fructose

  • fructose is a ketohexose
  • HFCS contains 55% fructose and 42% glucose (used as sucrose substitute in soft drinks)

13

describe maltose

  • maltose = 2 glucose units
    • linked by an a1->4 glycosidic linkage
  • maltose is a reducing sugar

14

contrast homopolysaccharides and heteropolysaccharides

  • homopolysaccharides: similar monosaccharide units
    • starch, glycogen, cellulose (made up of glucose units)
  • heteropolysaccharides: different monosaccharide units
    • glycosaminoglycans/mucopolysaccharides

15

describe glycogen

storage polysaccharide

  • found in liver and muscles as cytosolic glycogen granules
  • the glucose units in the linear chain are linked by a1->4 glycosidic linkages and glucose units at the branch points are linked by a1->6 glycosidic linkages
  • glycogenin is the core protein surrounded by branches of glycogen with about 30,000 glucose units

16

describe starch

dietary polysaccharide

  • starch is made up of 2 components:
    • amylose (linear unbranched polymer of glucose)
    • amylopectin (branched polymer of glucose)
  • starch is made up of glucose units in the linear chain linked by a1->4 linkages. Glucose units at the branch point in amylopectin are linked by a1->6 linkages
  • starch is the major dietary polysaccharide digested by salivary and pancreatic amylase

17

contrast amylopectin and glycogen

  • amylopectin has fewer number of branches compared to glycogen
  • enzymes of glycogen metabolism act on the ends of the branches of glycogen and sequentially remove or add glucose from the ends of the glucose molecule

18

describe cellulose

  • majority of the dietary fiber is undigestible carbohydrate
    • examples are cellulose and pectin
  • cellulose is an unbranched homopolysaccharide containing glucose units linked by B1->4 linkages 
    • B1->4 linkages cannot be cleaved by digestive enzymes
  • lactase can hydrolyze the B1->4 linkages only in the dissacharide lactose--not in cellulose

19

describe glycoproteins

  • glycosylation may occur as either one type of linkage or with both on the same protein
  • O-linked
    • glycosylation on the OH group of Ser/Thr
    • often found as extracellular proteins/membrane bound
    • glycan groups always face extracellular side
  • N-linked
    • glycosylation on the Asn residue