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dmd 5241 > digestion absorption and transport of carbs > Flashcards

digestion absorption and transport of carbs Flashcards

1
Q

what family do all naturally occurring sugars belong to? all AA?

A

sugars: D

AA: L

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2
Q

define anomeric carbon

A

the asymmetric carbon in an aldose or ketose

  • aldose: carbon 1
  • ketose: carbon 2
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3
Q

what makes up a pyranose? a furanose?

A

pyranose: six membered ring (5 carbons, 1 oxygen)
furanose: 5 membered ring (4 carbons, 1 oxygen)

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4
Q

what causes cyclization?

A

the carbonyl carbon in a D or L form carb is highly reactive

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5
Q

which carbon is the reducing carbon?

A

1

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6
Q

what will allow a cyclized sugar to open up?

A

if the hydroxyl group on the anomeric carbon is not linked to another sugar by a glycosidic bond

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7
Q

name 3 polysaccharides discussed in class

A
  • starches
  • glycogen
  • cellulose
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8
Q

what are the 2 structural classes of starches?

A
  • amylose

- amylopectin

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9
Q

starches are polymers of?

A

alpha D glucose

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10
Q

what do starches serve as?

A

the carbohydrate storage form of plants

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11
Q

describe amylose

  • structure
  • linkage
A
  • linear chains of glucose molecules

- linked by alpha 1,4 bonds

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12
Q

describe amylopectin

  • structure
  • linkage
A
  • branched character in which linear chains of glucose molecules are occasionally linked alpha 1,6
  • only 5% are linked alpha 1,6
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13
Q

how much of starches are amylopectin and amylose?

A

amylopectin: 85%
amylose: 15%

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14
Q

what does glycogen serve as?

A

carbohydrate storage form in animals

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15
Q

describe glycogen

  • structure
  • where it is stored
  • where we get minute amounts from
A
  • resembles amylopectin, but more highly branched
  • primarily stored in liver and muscles
  • present in minute quantities in meat and fish
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16
Q

describe cellulose

A
  • chief constituent of fibrous parts of plants
  • composed of beta D glucose units in unbranched chains
  • indigestible and provides bulk in our diet
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17
Q

how are the following linked:

  • cellulose
  • glycogen
  • starches
A
  • cellulose: beta 1,4
  • glycogen: alpha 1,4
  • starches: alpha 1,6
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18
Q

name 3 disaccharides discussed in class

A
  • sucrose
  • lactose
  • trelahose
19
Q

what comprises (and what is the linkage) of:

  • sucrose
  • lactose
  • trelahose
A
  • sucrose: glucose linked to fructose via alpha, beta-1,2 bonds
  • lactose: galactose linked to glucose via beta-1,4 bonds
  • trelahose: two glucose molecules linked at their anomeric carbons via alpha,alpha-1-1 bonds
20
Q

between sucrose, lactose and trelahose, which one(s) are the reducing sugars? which monosaccharides are reducing? what does reducing sugar mean?

A

lactose is the only reducing sugar

all monosaccharides are reducing sugars

a reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group

21
Q

define dietary carbohydrate digestion

A

the enzymatic conversion of polysaccharides and disaccharides to their corresponding monosaccharides

22
Q

what enzymes catalyze digestion? how do they do it?

A
  • catalyzed by a family of enzymes known as glycosidases (glycoside hydrolases)
  • they hydrolyze glycosidic bonds
23
Q

what enzyme is contained in saliva?

A

salivary alpha-amylase (alpha-1,4 endoglucosidase)

24
Q

describe salivary amylase

A
  • randomly hydrolyzes the interior alpha-1,4 bonds between glucose
  • does so within amylopectin, amylose, and glycogen
  • converts polysaccharides to smaller entities
  • action is terminated by the acidic pH in the stomach
  • CANNOT cleave alpha-1,4 bonds at the end of a chain?
25
Q

what digestive enzymes are in the stomach?

what else may happen here?

A
  • there are no digestive enzymes in the stomach

- there may be some limited acid (nonenzymatic) hydrolysis of sucrose to yield fructose and glucose

26
Q

what are the two phases of digestion in the small intestine?

A
  • luteal phase

- membrane phase

27
Q

what triggers cholecystokinnin?

A

the presence of food in upper regions of the small intestine

28
Q

what does cholectstokinnin do?

A
  • acts on endocrine cells of the pancreas to release digestive enzymes including a pancreatic alpha-amylase
29
Q

what does pancreatic alpha-amylase do?

A

continues the digestion of starch in the small intestine

30
Q

what is secretin? what generates its response? what does it do?

A
  • secretin is a peptide hormone
  • generated by low pH of gastric contents entering the intestine
  • it causes the pancreas to release to release a solution rich in bicarb that neutralizes the pH of the intestinal contents
31
Q

what are the final products of pancreatic alpa-amlylase?

A
  • maltose
  • maltotriose
  • branched dextrins
32
Q

what happens in the luminal phase?

A
  • peptide hormone cholecystokinin is produced
  • cholecystokinin acts on exocrine cells of pancreas to release alpha-amylase
  • other cells produce secretin, another peptide hormone
    secretin that causes the pancreas to release bicarb
  • pancreatic alpha-amylase continues the digestion of starch
33
Q

which exoenzymes cleave off one monosaccharide at a time? which end do they cleave?

A
  • lactase
  • trehalase
  • glucoamylase
  • sucrose-isomaltase
  • they cleave the NONreducing end
34
Q

which saccharides are digested by epithelial cells in the intestinal villi?

A
  • lactose
  • sucrose
  • maltose
  • maltotriose
  • dextrins
35
Q

what do the following cleave?

  • lactase
  • trehalase
  • glucoamylase
  • sucrase-isomaltase
A
  • lactase: beta-1,4 bond between galactose and glucose in lactose
  • trehalase: alpha,alpha-1,1 bond in trehalose to yield 2 molecules of glucose
  • glucoamylase:
    • alpha-1,4 linkages between glucose units in oligosaccharides starting from nonreducing end
    • alpha-1,4 bonds in maltose and maltotriose to yield glucose
  • sucrase-isomalate
    • sucrase site hydrolyzes sucrose to form glucose and fructose
      • maltase activiry
    • isomaltase site hydrolyzes alpha-1,6 bonds between glucose residues
      • maltase activity
36
Q

what does dietary fiber refer to? how is it grouped?

A
  • carbohydrates or carbohydrate derivatives of plant origin which are not hydrolyzed by digestive enzymes
  • grouped into 2 main categories
    • soluble and insoluble in water
37
Q

what is included in soluble fiber?

A
  • pectins
  • mucilages
  • gums
38
Q

what is included in insoluble fibers?

A
  • cellulose
  • hemicellulose
  • lignin
39
Q

what is formed from undigested carbohydrates? what metabolizes these?

A

formed: gases, short chain fatty acids, lactate

gases:
- CO2
- H2
- methane

short chain fatty acids:

  • acetic
  • propionic
  • butyric

lactate

40
Q

what are the benefits of fiber?

A
  • reduces colon cancer (fiber binds to suspected carcinogens
  • pectins lower cholesterol levels by binding to bile acids
  • pectins may slow the rate of absorption of glucose (this will prevent high blood glucose levels after meals)
  • softens the stool, reducing the pressure on the colonic wall in diverticular disease
  • useful for patients with irritable bowel syndrome
41
Q

what are the major carbohydrate constituents in the US diet?

A
  • starch
  • sucrose
  • lactose
42
Q

what are the linkages for:

  • starch
  • glycogen
  • cellulose
  • sucrose
  • lactose
  • trehalose
A
  • starch: alpha-1,4 and alpha-1,6
  • glycogen: alpha-1,4 and alpha-1,6
  • cellulose: beta-1,4
  • sucrose: alpha,beta-1,2
  • lactose: beta-1,4
  • trehalose: alpha,alpha-1,1
43
Q

what units make up:

  • starch
  • glycogen
  • cellulose
  • sucrose
  • lactose
  • trehalose
A
  • starch: alpha-D-glucose units
  • glycogen: alpha-D-glucose units
  • cellulose: beta-D-glucose
  • sucrose: glucose linked to fructose
  • lactose: galactose linked to glucose
  • trehalose: two glucose molecules linked together
44
Q

what cleaves maltose? what are the products?

A
  • cleaved by sucrase-isomaltase glucoamylase

- products are: 2 glucose molecules

dmd 5241 (3 decks)

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