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dmd 5241 > digestion absorption and transport of carbs > Flashcards

digestion absorption and transport of carbs Flashcards

(44 cards)

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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

Study These Flashcards
A
  • sucrose
  • lactose
  • trelahose
19
Q

what comprises (and what is the linkage) of:

  • sucrose
  • lactose
  • trelahose
Study These Flashcards
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?

Study These Flashcards
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

Study These Flashcards
A

the enzymatic conversion of polysaccharides and disaccharides to their corresponding monosaccharides

22
Q

what enzymes catalyze digestion? how do they do it?

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

what enzyme is contained in saliva?

Study These Flashcards
A

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

24
Q

describe salivary amylase

Study These Flashcards
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
what digestive enzymes are in the stomach? what else may happen here?
- there are no digestive enzymes in the stomach | - there may be some limited acid (nonenzymatic) hydrolysis of sucrose to yield fructose and glucose
26
what are the two phases of digestion in the small intestine?
- luteal phase | - membrane phase
27
what triggers cholecystokinnin?
the presence of food in upper regions of the small intestine
28
what does cholectstokinnin do?
- acts on endocrine cells of the pancreas to release digestive enzymes including a pancreatic alpha-amylase
29
what does pancreatic alpha-amylase do?
continues the digestion of starch in the small intestine
30
what is secretin? what generates its response? what does it do?
- 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
what are the final products of pancreatic alpa-amlylase?
- maltose - maltotriose - branched dextrins
32
what happens in the luminal phase?
- 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
which exoenzymes cleave off one monosaccharide at a time? which end do they cleave?
- lactase - trehalase - glucoamylase - sucrose-isomaltase - they cleave the NONreducing end
34
which saccharides are digested by epithelial cells in the intestinal villi?
- lactose - sucrose - maltose - maltotriose - dextrins
35
what do the following cleave? - lactase - trehalase - glucoamylase - sucrase-isomaltase
- 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
what does dietary fiber refer to? how is it grouped?
- 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
what is included in soluble fiber?
- pectins - mucilages - gums
38
what is included in insoluble fibers?
- cellulose - hemicellulose - lignin
39
what is formed from undigested carbohydrates? what metabolizes these?
formed: gases, short chain fatty acids, lactate gases: - CO2 - H2 - methane short chain fatty acids: - acetic - propionic - butyric lactate
40
what are the benefits of fiber?
- 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
what are the major carbohydrate constituents in the US diet?
- starch - sucrose - lactose
42
what are the linkages for: - starch - glycogen - cellulose - sucrose - lactose - trehalose
- 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
what units make up: - starch - glycogen - cellulose - sucrose - lactose - trehalose
- 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
what cleaves maltose? what are the products?
- cleaved by sucrase-isomaltase glucoamylase | - products are: 2 glucose molecules

dmd 5241 (3 decks)

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